CHAPTER 13

WATER HARDNESS

AND HEALTH EFFECTS

=ONTENTS

L Definition of Water Hardness

I Natural Hydrochemical Evolution of Groundwater

II The Hard-Water Story

Studies at an Individual Level

Physiological Importance of Magnesium

1 Magnesium Intake

11 Water Magnesium and Body Magnesium Status

n Calcium in Drinking Water and Cardiovascular Disease

X Water Hardness and Other Health Effects

Conclusions and Consequences

DEFINITION OF WATER HA RDNESS

ter hardness is the traditional measure of the PJcity of water to react with soap and describes the li ty of water to bind soap to form lather which is a ~mical reaction detrimental to the washing process lrdness has little significance in terms of hydrocbemshyI studies but it is an important parameter for water

15 Today the technical significance of water hardshy- is more concerned with the corrosive effects on er pipes that carry soft water

II vj ll(Ii(I G(gy 331

EVA RUBDIOWITZ-LuNDIN

Giitcborg Univerity

KEVIN M HISCOCK

UJlivelsi~) of East Anglia

Despite the wide usage of tlle term tlle property of hardness is difficult to define exactly Vater hlrdness is not caused by a single substance but by a variety of dissolved polyvalent metallic ions-predominantly ca lcium 111d magnesium-although otller ions for example aiuminulll barium iron manganese stronshytiulll lnd zinc llso contribute The source of the metallic ions are typically sedimentary rocks and the most common are limestone (CaCO ) and dolomite (CaMg(CO)J

Hardn ess is normally expressed as the total concenshynation of calcium 1lld magnesium ions in water in units ofmgL- as equivalent CaCO Hardn ess can be detershymined by substituting the concentration of calcium and magnesium expressed in 111g I I in the following equation

Total hardness = 25(Ca 2middot)+41(lvIgZ~ ) (1)

Each concentration is multiplied by the ratio of the formula weight of CaCO to the atomic weight of the ion hence the factors 25 and 41 are included in th e hardness relation (Freeze amp Cherry 1979)

In Europe Wlter hardness is often expressed in terms of degrees of hardness One French degree is equivalent to 10mgL- as CaCO one German degree to 178 mg L -1 as CaCOl and one E nglish of Clark degree to 143 mg L - I as CaCOJbull One German degree of hardness (dH) is equal to 1mg of calcium oxide (CaO) or 072 mg ofmagnesium oxide (MgO) per 100 mL ofWJter

Copyright copy 2005 Elsevier Ille Al1 ri ghts resened

332 VIATEll H ~RD-LSS AND

There reported carbonate hardness includes that part of the total hardness equivalent to the bicarbonate and carbonate (or ltllkalinity) If the hardness exceeds the ltllblinity the excess is called the non-carbonate hardshyness and is a measure of the calcium and magnesilU11 sulfates In older publications the terms temporary and permanent are used in place of carbonate and non-carbonate Temporary hardness reflects the fact that the ions responsible may be precipitated by boiling such that

A number of attempts have been made to classi~l water bardncssrater vith hardness values greater than 150 mg L - I is designated as very hard Soft water has values of less than 60mg L- G roundwaters in contact with limestone or gypsum (CaSO~2HO) rocks can commonly attain levels of 200-300mg L- In water from gypsiferous forma tions 1000 mg1- 1 or more of total hardness may he present (Hem 1985)

H ardness in water used for domestic purposes does not become particularly troublesome until a level of 100mg L- is exceeded D epending on pH and alkalinshyity har Iness of about 200 mg L- I can result in scale deshyposition particularly on heating and increased soap consumption Soft waters with a hardness of less than about 100mgL- have a low buffering capacity and may be more corrosive to water pipes resulting in the presshyence of heavy metals such as cadmium copper lead and zinc in drinking water This depends on the pH alkashylinity wd dissolved oxygen concentration of the water

o health-based guideljne value is proposed for hardshyness because it is considered that the available data on the inverse relationship between the hardness of drinking water and cerebrovascular disease (CVO) are inadequate to permit the conclusion that tbe association is causal (VVH O 2002) However a concentration of 500mgL- is at the upper limit of aesthetic acceptability

II NATU RAL HVDROCH E M ICAL

EVOLUTION OF GROU N D W ATER

T he combination of geology and hydrology of a river catchment is important in determining the hardness of water As illustrated in Figure lA catchments underlain by impermeable rocks that are resistant to erosion genshyerate surface runoff with little time for weathering to

occur s a result the surface water has a chemical com-

HEALTH ErHcTS

A

B

FIGURE Illustration of two types of water resources and the influence of catchment geology on water hardness In (A) surface water runoff from the impermeable Silurian mudstones

and siltstones to the Dinas reservoir in west Wales is a soft water with a hardness of 19 mg L I as CaCOJ pH of 70 and

electrical conductivity of 73 pS cm I (sample date 1998 Hiscock amp Paci 2000) In (B) groundwater discharge from the Fergus River Cave springs developed in Carboniferous limestone in

County Clarelreland is a very hard water with a hardness of 256mgL- as CaCO) pH of 77 and electrical conductiVity of

440 JiS cm- I (sample date 2002)

position similar to dilute rainfall and is chanlcterized as soft water In contrast and as illustrated in Figure 1B catchments underlain by permeable rocks all 0 water to infiltrate below the ground surface such that groundshywater in contact with the rock mas promotes solutional weathering which potentially leads to the development of fissures and conduits As a result the groundwater attains a high concentration of dissolved constituents and is characterized as hard vater

Tn natural aqueous systems the chemical composition of water is continually changing and is controlled preshy

VVATER HARD-ESS

unmimll1tly by geologiGll factors The geochemistry of rock weathering determines the release of elements into water In groundwaters a natural evolution of chemical composition is recognized Dilute rainwater with a odium chloride water type and contailling CO2 enters

e soil zone whereupon further CO2 produced by the Jecay of organic matter is dissolved in the inllltnlting middot Her to form carbonic acid vVithin the soil and Ul1satshyJrltlted zone of sedimentary rocks tbis weak acid disshyohes soluble calcium and magnesium carbonates such J calcite and dolomite to give high concentrations of alciul11 magnesium and bicarbonate In crystalline

~1l eous and metamorphic rocks slow wCltlthering of silshycd tes by the attack of carhonic acid releases low conshy

x lltrations of calcium magnesium potassium and i)diUlll in the infiltrating soil water or groundwater and h o produces bicarbonate

-way from the supply of oA)gen in the soil and unsatshyrated zone infiltrating water becomes increasingly noxic as a result of progressive bacterial recluction

oxygen Below the water table and with increasing _ducing conditions iron and manganese become

nhili zed and then later precipitated as metal sulfides the presence of disseminated clay material within an qui fer ion exchange replaces calcium for sodium as

e water evolves to a sodium bicarbonate water type lence the grounclwater is naturally softened by ion

hange reactions In the deeper confined section of ui fers mixing with saline water may occur to produce odiull1 chloride water type before a region of static Jtt r and aquifer dingenesis is reached Either pnrt or

o f this classic sequence of hydrochemical change Identified in a number of aquifers including the Iridl1l aquifer system The Floridan aquifer system occurs in the southeast ired States (Figure 2) and is one of the most proshy ti lmiddote aquifers in the world The aquifer system is a

_-ticaJly continuous sequence of Tertiary carbonate L~ of generally high permeability Limestones and lDlites are the principal rock types although in _~h I estcrn and northeastern Georgia and in South o]jna the limestones grade into lime-rich sands and _ The Florichl11 aquifer is composed primarily of ~ ~e mel dolomite with minor gypsum apatite glaushy

- middotrt quartz clay minerals and trace amounts of it oxides and suI fides

ThL total hardness of water in the U pper Floridan _r aries from lt50 to gt5000mgL- as CaCO JJJ~ where the system is composed only of Jimeshy

~ _ the total hardness is equivalent to carbonate ~lIld is ltl20mgL- I

Groundwater with higher -artiness usually results from (1) dissolution of

A-D HEALTH E PFE CTS 333

other aquifer minerals primarily dolomite and gypsum (2) mixing of fresh water with residual saline groundshywater (3) encroachment and mixing of modern seawashyter or (4) contamination Na tural softening of the groundwater hy cation exchange is thought to be responsible for the low hardness in Escambia and Santa Rosa Counties Florida (Sprinkle 1989)

A sequence of hydrochemical evolution is identified hy Sprinkle (1989) which start~ with calcite dissoluti on in recharge areas that produces a calcium-bicarhonate dominated water type with a total dissolved solids (TOS) concentration of generaLly less than 250 mg L- Oowngradient dissolution of dolomite leads to a calciul11-magnesium-bicarhonlte water type here gypsum is abundant sulfate becomes the predominant anion In coastal arens as shown in Figure 3 seawater increases the TDS concentration and the water type changes to sodium-chloride In the western panhandle of Florida cation exchange leads to the development of a sodium-bicarbonate water type and a less hard groundwater

For additional reading on groundwater modeling see Modeling Groundwater Flow and Quality this volume

III TH E HARD-WATER S TO RY

The history behind what is considered today to be a commonly accepted fact-that hard water protects against CVD-is often referrecl to as the hard-water story The hard-water story started in 1957 wjth Jun Kobayashi a Japanese ngricultural chemist He had for many years been engaged in studies of the nature oflrrishygation water from all agricultural point of view In these studies he fOLlnd a close relation between the chemical composition of river water and the death rate from apoplexy (CVD) The death rate of apoplexy inJapan was extraordinarily high compared to other counuies and the biggest cause of death in Japan Kobayashi found that it was the ratio of sulfur to calmiddotbonate (SOjCaO) that was related to the death rate fr0111 apoplexy He suggested that inorgmic acid CaCO might induce or prevent apoplex) (Kobayashi 1957)

Three years later a study was presented by Schroeder (1960) comprising the 163 largest cities in the United States I-Ie found inverse correlations between water hardness and CVD in both men and women He aLso studied the relation between different water conshystituents and coronary heart disease (CHD) 11TI0ng 45shyto ()4-year-old men He found significant correlations

334 iVATER I-L~RD~ESS AND HLLTH EFFECTS

South Carolina Georgia

Alabama

Total hardness of water (mgL as CaC03)

1-1 0-60 (Soft)

1222161-120 (Moderately hard)

tmtI121-180 (Hard)

~ gt180 (Very hard)

-____ Limit of reliable data

Groundwater well

o 100 km I I

88deg 86deg 84

FIGU R E 2 Map of the extent of the Upper Floridan Aquifer showing the spatial distribution of total hardness of water Escambia and Santa Rosa Counties Florida are located at pOSitions E and SR respectively (After Sprinkle 1989)

between death rate from CHD and sulfate and hicarshybonate respectively but not for the ratio of the agents He also found significant negative correlations between deaths from CHD and magnesium calcium fluoride and pH The coefficient of correlation for magnesium in drinking water was r = -030 P lt001 and for calcium r = -027 P lt00 I (Schroeder 1960)

During the following decades several sUldies on the relation betveen water hardness and CVD were preshysented Initially the studies dealt with the question of Ihether there was a toxic effect in soft water or a proshytective effect in hard water As described above soft aters usually have low buffering capacity and are more corrosive which leads to higher amounts of toxic trace elements It has been proposed that this could account for the observed increased mortality However the results from previous studies have not supported this

hypothesis (lVlarier 1986a) For example in a nationshywide survey of more than 500 tap waters in Canada no significant correlation was found between mortality and trace elements like lead cadmium cobalt lithium mercury molybdenum nickel or vanadium (Neri et al 1975) Gradually it became obvious that it was a proshytective effect from hard water that was responsible for the relations seen In different parts of the world studies have bccn made on the relation betccn magshynesium and calcium in the local drinking water and CVD mortality These studies were generally based upon death registers and water data at regional or municipality levels The results of d1ese smdies are sumshymarizcd in T1ble 1

Even with these studies the results were not conclushysive as to the role of magnesium and calcium in drinking water for CVD Most of the studies showed a relation

VATER I-LRDXESS

1000----------------------------------

100

shyJ)

-

Q 10 I-=shy

12 r--- ~ j u

Ic ---I--f-----~~-~middotgt V o

1 7 I II 1 ~+-J

01

001

I Crewsville1 t

I i

20

CIshy

I Na+

I 11

Mg2+

1 1 SO~- I1 1 Ca2

1 +

-HCo

Distance (km) 60 80 100 120I Fort Ogden I

Avon Park Lake June South Punta in Winter Gorda Heights

A A

F IGURE 3 Hydrochemical section along lineA-A (for locashy In see Figure 2) showing the variation in concentrations of 2jor ions downgradient in the direction of groundwater flow - ~Iative to calcium and magnesium the groundwater experishy=~es an increasing concentration of sodium as a result of ion Ex-change and mixing with saline water in the coastal zone ~fter Sprinkle 1989)

_bull middoteen different cardiovascular deaths and either magshy ~iU111 or calcium or bOtJl but some studies showed no -da tion at aiL However most of these studies were ecoshy

rieal meaning that the exposure to water constituents J- determined at group levels with a high risk of misshy

aJJS ification Often very large groups for example all habitants in large cities or arcas were assigned the lTIe ltllue of water magnesium and calcium despite the

icnce of several waterworks or private wells

AKD HEALTH EFFECTS 335

TABLE J The Effect of High Magnesium (Mg) or Calcium (Ca) Levels in Drinking Water on the Mortality from Cardiovascular Disease (CVD) Coronary Heart Disease (CHD) or Cerebrovascular Disease (CD) in Different Studies Published since 1975

Mg Co

Studies CVD CHD CD CVD CHD CD

North America Dawson et al 1978 J J Neri et aI 1975

Great Britain Shaper et aI 1980 Maheswaran et aI 1999

Germany Teitge 1990

Sweden Nerbrand et al 1992 Rylander et aI 1991

South Africa Leary et aI 1983

J

J

J

J J J J

J

t = lower mortality - = no difference

In addition the disease diagnoses studied were someshytimes unspecific with wide definitions that included both cardiac and cerebrovascular diseases In some studics it is also unclear whether the range of magneshysium and calcium in drinking water W 15 large enough to allow for appropriate analyses

One of tJle most comprehensive studies of the geoshygraphic variations in cardiovascular mortality was the British Regional Heart Study The first phase of this study (Pocock et aL 1980) applied multiple regression analysis to the geographical variations in CVD for men and women aged 35-74 in 253 urban areas in England Vales and Scotland from 1969 to 1973 The investishygation showed that the effect of water hardness was nonLinear much greater in the range from very soft to medium-hard water than from medium to very hard water The geometric mean for the standardized mortality ratio (SMR) for CVD for towns grouped according to water hardness both with and without adjustments (by analysis of covariance) for tJle effects of four climatic and socioeconomic variables (percentage of days WitJl rain mean daily maximum temperature pershy

336 VATER HARD-ESS A-D HEALTH EFF ECT S

-- Unadjusted

- - - Adjusted for climate and socio-economic conditions

120

110

a 2 (j) 100 c ro Cll 2

90

80

10 50 90 130 170 210 250 290 Water hardness (mg L-1 as CaC03)

47 33 22 14 19 20 43 36 Number of towns

FIGURE 4 Geometric means of the standardized mortality ratio (SMR) (for all men and women aged 35-74 with CVD) for

towns in England Wales and Scotland grouped according to water hardness (in concentration units of mg L middot1 as CaCO)

equivalent) (After Pocock et al 1980)

centage of manual workers car ownership) is shown in Figure 4 The adjusted SMR decreased steadily in moving from a hardness of 10 to 170 mg L - I but changed little between 170 to 290 mg L- or greater After adjustshyment CVD in areas with very soft water around 25 mg L-1

W )5 estimated to be 10-15 higher than in areas with medium-hard water around 170 mg L- I whereas any further increase in hardness heyond 170 mg L -I did not additionally lower CVD mortality Hence it appeared that the maximum effect on CVD WIS princishyP)lly between the very soft and medium-hard waters Adjusting for climatic and socioeconomic differences considerably reduced the apparent magniulde of the effect of water hlrdness (Pocock et al 1980)

A problem with correlation studies such as the British Regional Heart Study as argued by Jones and Moon (1987) is the t~lilure of much of the research to consider the causal mechanism that links independent variables to the disease outcome Also many of the calibrated models presented in tlle literature are socially blind in including only variables pertaining to the physical envishyronment which often contributes a large number of water qua Ii ty elements Even in those better analyses that have included social varilhles as in the case of the British Regional Heart Study the relatively strong corshyrelation found for calcium in England and Vales may be a result of calcium acting as a rery good surrogate for social variables The soft water areas of the north and west of the British Isles equate to tlle areas of early

100r-------------------------------------~

90 0 Suriyawewa

80 ~ Uda Walawe j( =395 mg L-1 as CaC03 (n =102)

~ Ridiyagama70i 60 u ~ 50 J

g 40 tt

30

20

10

O +-~~~~~~~-L~~~-L~~Lr~~~~

0-60 61-150 151-500 501 - 1000 gt1000

Total hardness (mg L -I as CaC03)

FIGURE 5 Histogram of total hardness values recorded for

groundwaters sampled during the wet season Uanuary and Febshyruary 200 I) from dug wells and tubewells in three subcatchments

of the Uda Walawe basin of Sri Lanka (Data courtesy of L Rajashysooriyar)

industrialization and today these areas house a disproshyportionate percentlge of the socially disadvantaged Gones amp Moon 1987) Therefore it is important thar further smdies undertake tlle challenge of quantitatively analyzing the seplrate effects of social variables fro111 those of water hardness

Fewer sUldies have been carried out in developing countries but Dissanayake et al (1982) for example found a negative correlation beveen water harclness and vlrious forms of CVD and leukemia in Sri Lanb N[ore recent sUldies (Dissanayake 1991 Rajasooriy~lr 2(03) have highlighted the problem of high fluoride concentrations and associated dental fluorosis in areas of hard water abstracted from crystalline bedrock aquifers in Sri Lanka

Rajasooriyar (2003) measured total hardness in dug vells and tubewelJs in the Uda vValawe basin of southern Sri Lanka in the wide range of7-3579mgL-1 as CaCO with an average of 395 mgL- as CaCO (Figure 5) Compared with the government water quality limit of 600 11lgL- as CaCO 12 ofthe 102 samples collected during tlle wet season in 2001 were in excesS of the limit and are considered too hard to drink (values above 100- 150mg-L-1 as CaCO j are 10cltllIy considered too hard as a water supply) Soft waters are found in are)s with a dense irrigation netvork supplied by rain-fed surface reservoirs Irrigation canal waters in the Suriyavewa and Ucla vValawe subcatchments were measshyured in the dry season to have a total hardness in the range 40-90mgL-1 as CaCO) (Rajasooriyar 2(03) and it is leakage of this water source that leads to tlle softenshy

337tVATpoundll HARDNESS AJD HEALT il EffECTS

ing ofshlllow grmmdwater The majority of the groundshywaters (63 ) in the fractured aqujfer represent very hard -lter with carb()l1ate hardness in the range 151- 500 mg L- ~s CaCO) contributed by the weathering of ferroshymagnesian minenJls anorthite calcite and dolomite T he products of this weathering lead to high concentrashytions of dissolved calcium magnesilllll and bicarbonate in gronndwaters E xceptionally high values of hardness gt 1O()OmgL - I as CaC03) typiCltl11y occur in non-irrishy

l tecl areas with additional non-carbonate hrrdness COllshy

rr ibuted by pyrite oxidation and in the case of the coastal Ri diyagam coastal catchment by salt water inputs

IV S TUDIES AT AN INDIVIDUAL LEVEL

In recent years some studies have been made with a igher precision as regards exposure classification than he previously cited ecological studies Most of them 3-e been conducted with a case-control design This

1I1S thlt the exposure to water magnesium and l icium has been estimated for i11dividuals who have uttered from the disease as well as for healthy control

-cr ons and the difference in risk calculated A simil lr Pc of study design is the prospective cohort study here the subjects are followed over time

Studies in Finland

lTI ltar and Karvonen 111lde a cohort study in 1979 I-te ~ compared the denh rate from CHI) in two rural

alt in vestern and eastern Finland The cohort -nprised men 40-59 years old in J 959 and they were ilOlred for 15 years The water data were not truly Ji-idual but were median volues in ten suhareas in the

[ern 1rea md 33 SUblleaS in the eastern area The ges of sUbltllmiddotel medians were 69- 27R I11g L - I of ter magnesium in the western area and O6- 73mgL-1

~he eastern area The cohort in eastern Finland had _ath rate hmiddotom CHD which was 1 7 times higher than

- estern cohort C alcium was not investigated few years Later Luoma et a (J983) published a

_ -control study conducted in the southeastern region - Fi nland Cases were men 30-04 year~ of age with

rt 1cute myocardial infarction (AMT alive or tlS t d) who were pair-matched with hospital conshy

fo r age and region (rmal vs urban) L1 addition ub tion controls vcre selected and matched for age m unjcipality All subjects submitted a sample of

their drinking water The range of magnesium in the drinking water was 10- 575 mgL- for the cases and 075-300mgL- and l0-160mgL- for the hospital controls and population controls respectively For caseshypopulation control comparisons the relative risk (RR) with 95deg) confidence limjts was 47 (9510 confidence interval [ell J3-253) for magnesiull1levels lower than l2 mgL - 1

bull This means that those with the lowest magshynesium levels had a risk of AiVil almost fi ve times higher than those with higher magnesium lerels For the caseshyhospital control comparisons the RR was 20 (95 CI 07- 65) that is double the risk They also found inverse relations vith fluoride levels but no relation to calcium

B Studies in Sweden

In Sweden three case-control studies have heen conshyducted during the last decade First using mortality registers the rebtion between death from AMI and the level of magnesium and calcium in drinking water was examined among men A few years later a study with a similar design WlS made comprising women The studies were conducted in southern Sweden in a relashytively small geographic area where there was a great difference between as well as within the municipalities regarding magnesium and calcium content in drinking w~lter The advantage with this lirnited study area was that the possible risk of such confounding factors as climate geographical cultural and socjoeconomic difshyferences was minimized

Seventeen municipalities were identified whose water quality vith respect to water hardness acidity and treatment procedures had been basically unchanged (change of hardness lt10 and pH lt5 ) during the most recent ten years Figure 6 shows the location of tbe 17 mUL1icipalities that comprised the study area

Cases vere men (n = 854) and women (n = 378) in 17 municipalities in southern Sweden who had died of AiVIJ between ages 50 and 69 years Controls were men (n =989) and women (n = 1368) of the same age group who had died of cancer LJdividnal water data were colshylected l~lhle II shows the number of vaterworks the range of magnesium in drinking water and the amount of magnesium in water supplied to the most densely populated area in each municipality

The subjects -were divided into quartiles according to

the levels of magnesium Odds ratios were calcula ted in relation to the group with the lowest exposure Adjustshyments for age were ll1ade in aU analyses The results show odds ratios of 065 for men and 070 for women in the quartile with highest magnesium levels in the

N

I

bull

F IGURE 6 The country of Sweden with SIlaquoine and Blekinge counties enlarged The 17 municipalities ill the studies are numbered corresponding to Table II ie I Vellinge 2 Svedala 3 Skurup 4 Hbbr 5 Ystad 6 Trelleborg 76 Gbinge 8 6rkelljunga 9 Bromblla 10 Perstorp I I Klippan 12 Astorp 13 Kristianstad 14 Sirnrishamn 15 Angelholm 16 Karlskrona and 17 Karlshamn

drinking water (298-99mgL-) (Figure 7) This meansT AB LE II Number of Waterworks Range of that the ri sk of dying from M I was about 30 lowerMagnesium (Mg) Concentrations in Drinking Water compared with the risk for those who used drinking(mgL- ) and Amount of Mg in Water Supplied to the water with the lowest levels of magnesium (RubenowitzMost Densely Populated Areas (mgL-) et al 1996 1999)

A few years later a prospective interview study was Water Mg in the conducted in the same area where men and women who

Number of Range of most densely suffered from AM I from 1994 to 19 were compared Municipality waterworks water Mg populated area with population controls (Rllbenowitz et al 20(0) The no in the study (mgL-I) (mgL I) results showed that magnesium in drinking water proshy

tected against death from AM I but the total incidence 2 59-100 100 was not affected In particular the number of deaths

2 2 68-200 200 outside hospitals was lower in the quartile with high 3 4 26-100 90 fllelgnesiurn levels This supports the hypothesis that 4 2 88-130 88

magnesium prevents sudden death from ANI rather5 5 5 1-119 75

than all CHD deaths The mechanisms that could6 4 65-180 160 explain these findings are discllssed below 7 9 33-135 50

8 3 30-69 69

9 5 13-76 13 10 2 40-90 90 II 2 55-90 80 V PHYSIOLOGICAL IM PORTA N CE 12 100 100

OF MAGNESIUM13 15 13-144 67 14 9 38-134 97

15 2 70-110 110 A Physiological Properties of 16 9 20-130 20

Magnesium in Humans17 2 19-50 20

Municipality numbers correspond to Figure 6 11agnesium is involved in several important enzymatic reactions All reactions that involve ATP (adenosine triphosphate) thelt is energy demanding reactions have an absolute magnesium requirement (Reinhardt 1988)

339 VATER HARDNESS AND H EALTH EFFECTS

OR men5 ----------------------------------------------------

0 100 1088 TI to651070

I_I )

0 --------c----------------=--=------------J s35 36-68 69-97 ~98

mg2- (mg L- )

OR women 5r ------------------~----------------------------~

108 100 0

093

r 1 r

70

5

0 s34 s35-67 68-9 8 ~99 mg2+ (mg L- )

F IGURE 7 Odds ratios (OR) with 95 confidence intervals Jr death from AMI in relation to magnesium in drinking water ~dj usted for age and calcium) in men and women

il nportant processes in the body mediated by magneshyi UJ1l are for example synthesis of protein nucleic acid nL fat glucose use neuromuscular transmission musshy

-u lar contraction and transport over cell membranes ]tura amp Altura 1996) (see also Chapter 30 this o lulle)

lagnesium is essential to the cardiovascular system nd two properties are especially important stabilizing

ilie cardiac electric system (preventing cardiac arrhythshymia) and regulating vascular tone (Reinhardt 1991) T here are multiple mechanisms behind these properties

lagnesium is needed to maintain the normal gradishy~nr of potassium and calcium over cell membranes ltura et aI 1981) It is well known that magnesium is

necessary to maintain intracellular levels of potassium T his is done by blocking the outward passage of potasshy-i Ulll through the cell membrane and by activating the ecnzvme NaK-ATPase It has a similar function in CashylTPase Magnesium also has a direct effect on potasshyiUIll and calcium channels in the cell membranes Reinhardt 1991)

Furthermore as regards impact on vascular tone Ilugnesium is a necessary activator for the synthesis of

cyclic adenosine monophosphate (c-Ai1P) which is a vasodilator It also acts as a natural calcium antagonist by competing for calcium binding sites in the vascular smooth muscle and thus reducing the constrictive effect of calcium in the blood vessels (Reinhardt 1991) In addition the vasoconstrictive actions of hormones such as angiotensin serotonin and acetylcholine are enhanced in the case of magnesium deficiency (Alhua et al 1981)

VI M AGNESIUM INTAKE

A Magnesium Deficiency

Marginal magnesium deficiency probably affects a large proportion of the population whose dietary intake does not reach the recommended amount Although severe magnesium deficiency is not common in the population hypomagnesemia is often present among hospitalized patients (Altura 1994) A survey showed that hyposhylIlagnesemia was the most common electrolyte abnorshymality in patients entering the intensive care unit and was present in 20 of the patients (Reinhardt 1988) (see also Chapter 8 this volume)

The causes of hypomagnesemia include reduced intake caused by starvation or intravenous therapy without magnesium supplement impaired absorption owing to chronic diarrhea or malabsorption syndromes increased renal loss caused by diseases such as diabetes or renal diseases or by the use of alcohol or such drugs as diuretics or antibiotics (Reinhardt 1988)

B Magnesium Intake From Food

The largest part of the total magnesium intake is from foodstuffs Magnesium is present in many foodshlffs and in large amounts in nuts beans green leafy vegshyetables and whole grain cereals Mainly because of increased industrial treatment which decreases magneshysium levels by 80 to 95 (Marier 1986h) it has been suggested that the majority of people today have a lower magnesium intake than the recommended dietary amount (RDA) of 6 mg kg-I day-I (Marier 1986b Seelig 1986 Durlach 1989) Table III shows the magnesium content in some foodstuffs and beverages

Approximately 40 of magnesium ingested in food is normally absorbed (Hardwick et aL 1990) The proshyportion absorbed is inversely related to the amount ingested however and has been shown to range between approximately 10 and 70 (Fine et aL 1991)

340 VTER HARD-IESS A--D J-IMTII EFFECTS

TABLE II Magnesium (Mg) Content in Food and Beverages

Food items and Mg (mg Food items and Mg(mg beverages loog I) beverages fOOg- l

)

Food items Food items Bread white 23 Bananas 33 Bread fiber-rich 50 Fish 25 Muesli 100 Shrimp 42 Corn flakes 16 Meat 25 Cheese 34 Eggs 13 Common beans 184 Almonds 280

white dried Common beans 131 Peanuts 188

brown dried Corn 23 Dark chocolate 130 Spinach 79 Milk chocolate 60 Avocado 39 Broccoli 23 Beverages Tomato 10 Milk 12 Cucumber 10 Coffee 5 Mushrooms 13 Tea 3 Brown rice 110 Beer low alcohol 8

content White rice 34 Beer high alcohol II

content Potatoes 24 Red wine 12 Apples 5 White wine 3 Oranges 10 Spirits 0

Magnesium content in the water not included

The absorption rate also depends on the intake of other foodstuffs Elements such as calcium phosphorus fibers and phytic acids are known to diminish the absorption rate of magnesium (Seelig 1986) Most magnesium is absorbed in the distal small intestine mainly by passive diffusion through the panlCellubr pathway but also to a smaller extent by solvent drag and active transport (Hardwick et aI 1990)

VI I WAT E R MAGNESI U M AND

BODY MAGNES I U M STATUS

A Magnesium Intake From WatershyImportance for Body Magnesium Status

Vlagnesium has a natural source in water from the weathering of a range of rock types In igneous rock

magnesium is typically a constituent of the dark colored ferromagnesian minerals which include olivine pyroxshyenes ltlm phiboles and dark colored micas In altered rocks magnesian mineral species also occllr such 1S chlorite montmorillonite and serpentine Sedimentary forms of magnesium include magnesite (MgCO) and dolomite (CaiVIg(CO)) iVlagnesiulll is substantially less 1bunclant than calcium in all rock types and 0 in most natural waters the magnesium concentration is much lower usuall y by 5-10 times than the calciuIll concentration Concentrations of I11ltlgnesium in fresh waters are controlled by solution and precipitation reactions involving magnesiurn-bearing siJjcate and carbonate minerals with concentrations typically less than 50mgL-1

although values above IOOmgL I are recorded

Magnesium intake via water depends on the level in drinking water An important issue in discussions about the relation between vater magnesium and AMI is whether magnesium in drinking water can be critical for the body magnesiulll status as the main part of the magnes ium intake derives from food (Neutra 1999) It has been suggested th n the quantitative contribution of water magnesium may be crucial for body magnesium status for those who have a low dietary intake and use water with high magnesium levels (Durlach et aI 1989) L1 addition cooking food in magnesium-poor water leaches out magnesium while cooking in magnesiul1lshyrich water diminishes this loss (Haring amp 7a n Delft 1981)

Furthermore it has been suggested that magnesium in water appearing as hydrated ions has a higher bioavaila bility than magnesium in food which i bound ill different compounds that are less easily absorbed (Durbch et al 19H9 Theophanides et aI 1990) However simultaneous intake of other agents could diminish the absorption rate as discussed above

Plants cultivated in areas with magnesium-rich water may have higher magnesium content especially if the soil is magnesium-rich and the land is irrigated with magnesium-rich water People living in such areas who eat locally grown vegetables and fruits may also benefit from an addition to the total m1gnesium intake espeshycially during slimmer months H owever genetic factors appear to have a greater effect on plant magnesium composition than do soil and environmental factors (Vilkinson et aL 1987)

Some previous studies have shown relations between water magnesium and body magnesium content In a study of baboons tap water was more effective than dietary supplementation in increasing serum levels of magnesium and zinc (Robbins amp Sly 1981 ) Anderson

341 VATER HARDgtESS AKD HEALTH EFFE CTS

et 1 1 (1975) found relations between water magnesium md magnesium content in the hea rt muscle The m~ocardial ma gnesium was approximately 7 lower J l1ong residents of citi es with soft water T here lS however no difference in magnesium content in th e diaphragm or the pectoralis major muscle Other tudies have shown relations between water magnesium lecls and the magnesium content in skeletal ll1uscie and in coromllY lrteri es (Landin et aI 1989)

In a loading test 10 subjects who normally used water u ith a magnesium level of 16 mg L-I instead ve re given drinking wa ter with 20 I11g L - I magnesium Afte r six weeks of supplementation with l1lltlgnesium-enriched I lter the excretjon of magnesium wa s increased which indicated improved body magnesium status Ruhenmvitz et aI 1998)

nother study demonstrated that the ionized se rum magnesium level was rltlised after only six days of an increased di etltlry load of magnes ium but not the total hody magnesium However a correlation between ionized serum md ioni zed intracellular magnesium was 5hown (Altura amp Al tura 1996)

From the available data it is apparent that the quanshyriteltive contribution from water may be crll cial The m agnesiumlevcls in drinking water in the Swed ish caseshyontrol studies ranged from 0 to 44mgL- I Nith a tota l h ily intake of drinking water of two liters the proporshyjomll magnesium contribution from water thus ranges

from 0 to 88mgday- l This is a percentage contribution between 0 and 25 o f the RDA of 350mgday- l For those who hlVe 1 daily intake lower thaJ1 the RDA and m e magnesium-rich water the contribution would he (~ n more important

In the prospective study the calculated in take of lagnesium from food rell1ged from 15 7 to 658mgday-l

m edian 35 6mg day- I This means that a large number of the subjects had a lower intake than the RDA One gtubject with an intake of 157 mg magnesium per day used drinking water with 35mg L-l which mea ns a 15 addition to the magnesium intake from fo od If he instead had used water with 40 mg L - I the addishy

ti nn would have been 50 and the total daily intake ~-+o mg day- I

III C ALCIUM IN D RI N KI N G W ATER

N D CARDIOVASCULAR D ISEASE

T he majority of the previolls ecological studies showed 1n inverse rela tion hetween calcium in drinking water

and CVD 15 reported above The physio logical mechshy1l1isms thlt cou ld explain the reLltionship He not clear T here is hmveer evidence that calcium defici ency can cause hypertensi on vhich is a well-known risk factor for bo th stroke and A III (La u amp E by 1985 Vloore 1989 Vltl e lgter amp Brunner 1994)

A Calcium Deficiency

Calcium deficiency is common among the elde rl y espeshyci l lJy women The absorption nnd renal conscrvltl tion of calciu m decreases vith age The absorption of calcium from food varies between 15 and 75 (Schaafsma 1992) but in menolgtlt1l1sal wom en the absorption is only about 20- 30)) (Hemy amp Recker 1985) Furthermore cllciull1 intake is often decreased among the elderly (Harlan et aI 1984) The RDA for calcium in Sweden is 800 mg day- I for adult women and 600 mg day- I fo r men In the 1nited States the RDA is 1000-1 500 111g delyi for ad ults

stud ~ comprising 61000 women in Sweden e1 ged 40-76 showed that calcium intake decreased with age and thlt1t a majo rity of postmel1opausll women had a deficie nt calcium intake (1ichae lsson 1996) Several stud ies conducted in the United States have also shown an intake lower than recommended especially amo ng women (F leming amp Heimbach 1994) For individuals with a deficiency the additional cllciul1l fro lll water could be crucial to prevent this Along with the contrishybution of drin king water cooking food in Cltllcium-rich water has been shown not only to prevent lelching hut even to increlse ca lcium levels in rhe food (Ilaring amp van Delft 1981 )

B Calcium and Blood Pressure

Several studies have shown an inverse rebtion beteen dietary calciu111 in take and blood pressure fer3shyanalysis compri si ng l1early 40000 people ha s shown that a high calcium intake lowered both systo lic and diastolic hlood pressure (Cappucio et aI 1(95) Low serum concentrltl tions of ioni 7ed Gllcium have been me1sured in patien ts with hypertension ( IcCarron 1982) There are several possible 111 echlI1i sIllS that could expLlin how ca lcium lowers bl ood pressure

One mcchelllism 111lt1 y be that hypocalcemia inhihi ts C3-ATPlse activity which 1Clt1ds to an increase in fre e intracellular calci um and colltraction of vascubr smooth muscles (McCarron 198 5) Calcium supplementatio n has been shown to be efficaci ous especially among sa ltshy

332 VIATEll H ~RD-LSS AND

There reported carbonate hardness includes that part of the total hardness equivalent to the bicarbonate and carbonate (or ltllkalinity) If the hardness exceeds the ltllblinity the excess is called the non-carbonate hardshyness and is a measure of the calcium and magnesilU11 sulfates In older publications the terms temporary and permanent are used in place of carbonate and non-carbonate Temporary hardness reflects the fact that the ions responsible may be precipitated by boiling such that

A number of attempts have been made to classi~l water bardncssrater vith hardness values greater than 150 mg L - I is designated as very hard Soft water has values of less than 60mg L- G roundwaters in contact with limestone or gypsum (CaSO~2HO) rocks can commonly attain levels of 200-300mg L- In water from gypsiferous forma tions 1000 mg1- 1 or more of total hardness may he present (Hem 1985)

H ardness in water used for domestic purposes does not become particularly troublesome until a level of 100mg L- is exceeded D epending on pH and alkalinshyity har Iness of about 200 mg L- I can result in scale deshyposition particularly on heating and increased soap consumption Soft waters with a hardness of less than about 100mgL- have a low buffering capacity and may be more corrosive to water pipes resulting in the presshyence of heavy metals such as cadmium copper lead and zinc in drinking water This depends on the pH alkashylinity wd dissolved oxygen concentration of the water

o health-based guideljne value is proposed for hardshyness because it is considered that the available data on the inverse relationship between the hardness of drinking water and cerebrovascular disease (CVO) are inadequate to permit the conclusion that tbe association is causal (VVH O 2002) However a concentration of 500mgL- is at the upper limit of aesthetic acceptability

II NATU RAL HVDROCH E M ICAL

EVOLUTION OF GROU N D W ATER

T he combination of geology and hydrology of a river catchment is important in determining the hardness of water As illustrated in Figure lA catchments underlain by impermeable rocks that are resistant to erosion genshyerate surface runoff with little time for weathering to

occur s a result the surface water has a chemical com-

HEALTH ErHcTS

A

B

FIGURE Illustration of two types of water resources and the influence of catchment geology on water hardness In (A) surface water runoff from the impermeable Silurian mudstones

and siltstones to the Dinas reservoir in west Wales is a soft water with a hardness of 19 mg L I as CaCOJ pH of 70 and

electrical conductivity of 73 pS cm I (sample date 1998 Hiscock amp Paci 2000) In (B) groundwater discharge from the Fergus River Cave springs developed in Carboniferous limestone in

County Clarelreland is a very hard water with a hardness of 256mgL- as CaCO) pH of 77 and electrical conductiVity of

440 JiS cm- I (sample date 2002)

position similar to dilute rainfall and is chanlcterized as soft water In contrast and as illustrated in Figure 1B catchments underlain by permeable rocks all 0 water to infiltrate below the ground surface such that groundshywater in contact with the rock mas promotes solutional weathering which potentially leads to the development of fissures and conduits As a result the groundwater attains a high concentration of dissolved constituents and is characterized as hard vater

Tn natural aqueous systems the chemical composition of water is continually changing and is controlled preshy

VVATER HARD-ESS

unmimll1tly by geologiGll factors The geochemistry of rock weathering determines the release of elements into water In groundwaters a natural evolution of chemical composition is recognized Dilute rainwater with a odium chloride water type and contailling CO2 enters

e soil zone whereupon further CO2 produced by the Jecay of organic matter is dissolved in the inllltnlting middot Her to form carbonic acid vVithin the soil and Ul1satshyJrltlted zone of sedimentary rocks tbis weak acid disshyohes soluble calcium and magnesium carbonates such J calcite and dolomite to give high concentrations of alciul11 magnesium and bicarbonate In crystalline

~1l eous and metamorphic rocks slow wCltlthering of silshycd tes by the attack of carhonic acid releases low conshy

x lltrations of calcium magnesium potassium and i)diUlll in the infiltrating soil water or groundwater and h o produces bicarbonate

-way from the supply of oA)gen in the soil and unsatshyrated zone infiltrating water becomes increasingly noxic as a result of progressive bacterial recluction

oxygen Below the water table and with increasing _ducing conditions iron and manganese become

nhili zed and then later precipitated as metal sulfides the presence of disseminated clay material within an qui fer ion exchange replaces calcium for sodium as

e water evolves to a sodium bicarbonate water type lence the grounclwater is naturally softened by ion

hange reactions In the deeper confined section of ui fers mixing with saline water may occur to produce odiull1 chloride water type before a region of static Jtt r and aquifer dingenesis is reached Either pnrt or

o f this classic sequence of hydrochemical change Identified in a number of aquifers including the Iridl1l aquifer system The Floridan aquifer system occurs in the southeast ired States (Figure 2) and is one of the most proshy ti lmiddote aquifers in the world The aquifer system is a

_-ticaJly continuous sequence of Tertiary carbonate L~ of generally high permeability Limestones and lDlites are the principal rock types although in _~h I estcrn and northeastern Georgia and in South o]jna the limestones grade into lime-rich sands and _ The Florichl11 aquifer is composed primarily of ~ ~e mel dolomite with minor gypsum apatite glaushy

- middotrt quartz clay minerals and trace amounts of it oxides and suI fides

ThL total hardness of water in the U pper Floridan _r aries from lt50 to gt5000mgL- as CaCO JJJ~ where the system is composed only of Jimeshy

~ _ the total hardness is equivalent to carbonate ~lIld is ltl20mgL- I

Groundwater with higher -artiness usually results from (1) dissolution of

A-D HEALTH E PFE CTS 333

other aquifer minerals primarily dolomite and gypsum (2) mixing of fresh water with residual saline groundshywater (3) encroachment and mixing of modern seawashyter or (4) contamination Na tural softening of the groundwater hy cation exchange is thought to be responsible for the low hardness in Escambia and Santa Rosa Counties Florida (Sprinkle 1989)

A sequence of hydrochemical evolution is identified hy Sprinkle (1989) which start~ with calcite dissoluti on in recharge areas that produces a calcium-bicarhonate dominated water type with a total dissolved solids (TOS) concentration of generaLly less than 250 mg L- Oowngradient dissolution of dolomite leads to a calciul11-magnesium-bicarhonlte water type here gypsum is abundant sulfate becomes the predominant anion In coastal arens as shown in Figure 3 seawater increases the TDS concentration and the water type changes to sodium-chloride In the western panhandle of Florida cation exchange leads to the development of a sodium-bicarbonate water type and a less hard groundwater

For additional reading on groundwater modeling see Modeling Groundwater Flow and Quality this volume

III TH E HARD-WATER S TO RY

The history behind what is considered today to be a commonly accepted fact-that hard water protects against CVD-is often referrecl to as the hard-water story The hard-water story started in 1957 wjth Jun Kobayashi a Japanese ngricultural chemist He had for many years been engaged in studies of the nature oflrrishygation water from all agricultural point of view In these studies he fOLlnd a close relation between the chemical composition of river water and the death rate from apoplexy (CVD) The death rate of apoplexy inJapan was extraordinarily high compared to other counuies and the biggest cause of death in Japan Kobayashi found that it was the ratio of sulfur to calmiddotbonate (SOjCaO) that was related to the death rate fr0111 apoplexy He suggested that inorgmic acid CaCO might induce or prevent apoplex) (Kobayashi 1957)

Three years later a study was presented by Schroeder (1960) comprising the 163 largest cities in the United States I-Ie found inverse correlations between water hardness and CVD in both men and women He aLso studied the relation between different water conshystituents and coronary heart disease (CHD) 11TI0ng 45shyto ()4-year-old men He found significant correlations

334 iVATER I-L~RD~ESS AND HLLTH EFFECTS

South Carolina Georgia

Alabama

Total hardness of water (mgL as CaC03)

1-1 0-60 (Soft)

1222161-120 (Moderately hard)

tmtI121-180 (Hard)

~ gt180 (Very hard)

-____ Limit of reliable data

Groundwater well

o 100 km I I

88deg 86deg 84

FIGU R E 2 Map of the extent of the Upper Floridan Aquifer showing the spatial distribution of total hardness of water Escambia and Santa Rosa Counties Florida are located at pOSitions E and SR respectively (After Sprinkle 1989)

between death rate from CHD and sulfate and hicarshybonate respectively but not for the ratio of the agents He also found significant negative correlations between deaths from CHD and magnesium calcium fluoride and pH The coefficient of correlation for magnesium in drinking water was r = -030 P lt001 and for calcium r = -027 P lt00 I (Schroeder 1960)

During the following decades several sUldies on the relation betveen water hardness and CVD were preshysented Initially the studies dealt with the question of Ihether there was a toxic effect in soft water or a proshytective effect in hard water As described above soft aters usually have low buffering capacity and are more corrosive which leads to higher amounts of toxic trace elements It has been proposed that this could account for the observed increased mortality However the results from previous studies have not supported this

hypothesis (lVlarier 1986a) For example in a nationshywide survey of more than 500 tap waters in Canada no significant correlation was found between mortality and trace elements like lead cadmium cobalt lithium mercury molybdenum nickel or vanadium (Neri et al 1975) Gradually it became obvious that it was a proshytective effect from hard water that was responsible for the relations seen In different parts of the world studies have bccn made on the relation betccn magshynesium and calcium in the local drinking water and CVD mortality These studies were generally based upon death registers and water data at regional or municipality levels The results of d1ese smdies are sumshymarizcd in T1ble 1

Even with these studies the results were not conclushysive as to the role of magnesium and calcium in drinking water for CVD Most of the studies showed a relation

VATER I-LRDXESS

1000----------------------------------

100

shyJ)

-

Q 10 I-=shy

12 r--- ~ j u

Ic ---I--f-----~~-~middotgt V o

1 7 I II 1 ~+-J

01

001

I Crewsville1 t

I i

20

CIshy

I Na+

I 11

Mg2+

1 1 SO~- I1 1 Ca2

1 +

-HCo

Distance (km) 60 80 100 120I Fort Ogden I

Avon Park Lake June South Punta in Winter Gorda Heights

A A

F IGURE 3 Hydrochemical section along lineA-A (for locashy In see Figure 2) showing the variation in concentrations of 2jor ions downgradient in the direction of groundwater flow - ~Iative to calcium and magnesium the groundwater experishy=~es an increasing concentration of sodium as a result of ion Ex-change and mixing with saline water in the coastal zone ~fter Sprinkle 1989)

_bull middoteen different cardiovascular deaths and either magshy ~iU111 or calcium or bOtJl but some studies showed no -da tion at aiL However most of these studies were ecoshy

rieal meaning that the exposure to water constituents J- determined at group levels with a high risk of misshy

aJJS ification Often very large groups for example all habitants in large cities or arcas were assigned the lTIe ltllue of water magnesium and calcium despite the

icnce of several waterworks or private wells

AKD HEALTH EFFECTS 335

TABLE J The Effect of High Magnesium (Mg) or Calcium (Ca) Levels in Drinking Water on the Mortality from Cardiovascular Disease (CVD) Coronary Heart Disease (CHD) or Cerebrovascular Disease (CD) in Different Studies Published since 1975

Mg Co

Studies CVD CHD CD CVD CHD CD

North America Dawson et al 1978 J J Neri et aI 1975

Great Britain Shaper et aI 1980 Maheswaran et aI 1999

Germany Teitge 1990

Sweden Nerbrand et al 1992 Rylander et aI 1991

South Africa Leary et aI 1983

J

J

J

J J J J

J

t = lower mortality - = no difference

In addition the disease diagnoses studied were someshytimes unspecific with wide definitions that included both cardiac and cerebrovascular diseases In some studics it is also unclear whether the range of magneshysium and calcium in drinking water W 15 large enough to allow for appropriate analyses

One of tJle most comprehensive studies of the geoshygraphic variations in cardiovascular mortality was the British Regional Heart Study The first phase of this study (Pocock et aL 1980) applied multiple regression analysis to the geographical variations in CVD for men and women aged 35-74 in 253 urban areas in England Vales and Scotland from 1969 to 1973 The investishygation showed that the effect of water hardness was nonLinear much greater in the range from very soft to medium-hard water than from medium to very hard water The geometric mean for the standardized mortality ratio (SMR) for CVD for towns grouped according to water hardness both with and without adjustments (by analysis of covariance) for tJle effects of four climatic and socioeconomic variables (percentage of days WitJl rain mean daily maximum temperature pershy

336 VATER HARD-ESS A-D HEALTH EFF ECT S

-- Unadjusted

- - - Adjusted for climate and socio-economic conditions

120

110

a 2 (j) 100 c ro Cll 2

90

80

10 50 90 130 170 210 250 290 Water hardness (mg L-1 as CaC03)

47 33 22 14 19 20 43 36 Number of towns

FIGURE 4 Geometric means of the standardized mortality ratio (SMR) (for all men and women aged 35-74 with CVD) for

towns in England Wales and Scotland grouped according to water hardness (in concentration units of mg L middot1 as CaCO)

equivalent) (After Pocock et al 1980)

centage of manual workers car ownership) is shown in Figure 4 The adjusted SMR decreased steadily in moving from a hardness of 10 to 170 mg L - I but changed little between 170 to 290 mg L- or greater After adjustshyment CVD in areas with very soft water around 25 mg L-1

W )5 estimated to be 10-15 higher than in areas with medium-hard water around 170 mg L- I whereas any further increase in hardness heyond 170 mg L -I did not additionally lower CVD mortality Hence it appeared that the maximum effect on CVD WIS princishyP)lly between the very soft and medium-hard waters Adjusting for climatic and socioeconomic differences considerably reduced the apparent magniulde of the effect of water hlrdness (Pocock et al 1980)

A problem with correlation studies such as the British Regional Heart Study as argued by Jones and Moon (1987) is the t~lilure of much of the research to consider the causal mechanism that links independent variables to the disease outcome Also many of the calibrated models presented in tlle literature are socially blind in including only variables pertaining to the physical envishyronment which often contributes a large number of water qua Ii ty elements Even in those better analyses that have included social varilhles as in the case of the British Regional Heart Study the relatively strong corshyrelation found for calcium in England and Vales may be a result of calcium acting as a rery good surrogate for social variables The soft water areas of the north and west of the British Isles equate to tlle areas of early

100r-------------------------------------~

90 0 Suriyawewa

80 ~ Uda Walawe j( =395 mg L-1 as CaC03 (n =102)

~ Ridiyagama70i 60 u ~ 50 J

g 40 tt

30

20

10

O +-~~~~~~~-L~~~-L~~Lr~~~~

0-60 61-150 151-500 501 - 1000 gt1000

Total hardness (mg L -I as CaC03)

FIGURE 5 Histogram of total hardness values recorded for

groundwaters sampled during the wet season Uanuary and Febshyruary 200 I) from dug wells and tubewells in three subcatchments

of the Uda Walawe basin of Sri Lanka (Data courtesy of L Rajashysooriyar)

industrialization and today these areas house a disproshyportionate percentlge of the socially disadvantaged Gones amp Moon 1987) Therefore it is important thar further smdies undertake tlle challenge of quantitatively analyzing the seplrate effects of social variables fro111 those of water hardness

Fewer sUldies have been carried out in developing countries but Dissanayake et al (1982) for example found a negative correlation beveen water harclness and vlrious forms of CVD and leukemia in Sri Lanb N[ore recent sUldies (Dissanayake 1991 Rajasooriy~lr 2(03) have highlighted the problem of high fluoride concentrations and associated dental fluorosis in areas of hard water abstracted from crystalline bedrock aquifers in Sri Lanka

Rajasooriyar (2003) measured total hardness in dug vells and tubewelJs in the Uda vValawe basin of southern Sri Lanka in the wide range of7-3579mgL-1 as CaCO with an average of 395 mgL- as CaCO (Figure 5) Compared with the government water quality limit of 600 11lgL- as CaCO 12 ofthe 102 samples collected during tlle wet season in 2001 were in excesS of the limit and are considered too hard to drink (values above 100- 150mg-L-1 as CaCO j are 10cltllIy considered too hard as a water supply) Soft waters are found in are)s with a dense irrigation netvork supplied by rain-fed surface reservoirs Irrigation canal waters in the Suriyavewa and Ucla vValawe subcatchments were measshyured in the dry season to have a total hardness in the range 40-90mgL-1 as CaCO) (Rajasooriyar 2(03) and it is leakage of this water source that leads to tlle softenshy

337tVATpoundll HARDNESS AJD HEALT il EffECTS

ing ofshlllow grmmdwater The majority of the groundshywaters (63 ) in the fractured aqujfer represent very hard -lter with carb()l1ate hardness in the range 151- 500 mg L- ~s CaCO) contributed by the weathering of ferroshymagnesian minenJls anorthite calcite and dolomite T he products of this weathering lead to high concentrashytions of dissolved calcium magnesilllll and bicarbonate in gronndwaters E xceptionally high values of hardness gt 1O()OmgL - I as CaC03) typiCltl11y occur in non-irrishy

l tecl areas with additional non-carbonate hrrdness COllshy

rr ibuted by pyrite oxidation and in the case of the coastal Ri diyagam coastal catchment by salt water inputs

IV S TUDIES AT AN INDIVIDUAL LEVEL

In recent years some studies have been made with a igher precision as regards exposure classification than he previously cited ecological studies Most of them 3-e been conducted with a case-control design This

1I1S thlt the exposure to water magnesium and l icium has been estimated for i11dividuals who have uttered from the disease as well as for healthy control

-cr ons and the difference in risk calculated A simil lr Pc of study design is the prospective cohort study here the subjects are followed over time

Studies in Finland

lTI ltar and Karvonen 111lde a cohort study in 1979 I-te ~ compared the denh rate from CHI) in two rural

alt in vestern and eastern Finland The cohort -nprised men 40-59 years old in J 959 and they were ilOlred for 15 years The water data were not truly Ji-idual but were median volues in ten suhareas in the

[ern 1rea md 33 SUblleaS in the eastern area The ges of sUbltllmiddotel medians were 69- 27R I11g L - I of ter magnesium in the western area and O6- 73mgL-1

~he eastern area The cohort in eastern Finland had _ath rate hmiddotom CHD which was 1 7 times higher than

- estern cohort C alcium was not investigated few years Later Luoma et a (J983) published a

_ -control study conducted in the southeastern region - Fi nland Cases were men 30-04 year~ of age with

rt 1cute myocardial infarction (AMT alive or tlS t d) who were pair-matched with hospital conshy

fo r age and region (rmal vs urban) L1 addition ub tion controls vcre selected and matched for age m unjcipality All subjects submitted a sample of

their drinking water The range of magnesium in the drinking water was 10- 575 mgL- for the cases and 075-300mgL- and l0-160mgL- for the hospital controls and population controls respectively For caseshypopulation control comparisons the relative risk (RR) with 95deg) confidence limjts was 47 (9510 confidence interval [ell J3-253) for magnesiull1levels lower than l2 mgL - 1

bull This means that those with the lowest magshynesium levels had a risk of AiVil almost fi ve times higher than those with higher magnesium lerels For the caseshyhospital control comparisons the RR was 20 (95 CI 07- 65) that is double the risk They also found inverse relations vith fluoride levels but no relation to calcium

B Studies in Sweden

In Sweden three case-control studies have heen conshyducted during the last decade First using mortality registers the rebtion between death from AMI and the level of magnesium and calcium in drinking water was examined among men A few years later a study with a similar design WlS made comprising women The studies were conducted in southern Sweden in a relashytively small geographic area where there was a great difference between as well as within the municipalities regarding magnesium and calcium content in drinking w~lter The advantage with this lirnited study area was that the possible risk of such confounding factors as climate geographical cultural and socjoeconomic difshyferences was minimized

Seventeen municipalities were identified whose water quality vith respect to water hardness acidity and treatment procedures had been basically unchanged (change of hardness lt10 and pH lt5 ) during the most recent ten years Figure 6 shows the location of tbe 17 mUL1icipalities that comprised the study area

Cases vere men (n = 854) and women (n = 378) in 17 municipalities in southern Sweden who had died of AiVIJ between ages 50 and 69 years Controls were men (n =989) and women (n = 1368) of the same age group who had died of cancer LJdividnal water data were colshylected l~lhle II shows the number of vaterworks the range of magnesium in drinking water and the amount of magnesium in water supplied to the most densely populated area in each municipality

The subjects -were divided into quartiles according to

the levels of magnesium Odds ratios were calcula ted in relation to the group with the lowest exposure Adjustshyments for age were ll1ade in aU analyses The results show odds ratios of 065 for men and 070 for women in the quartile with highest magnesium levels in the

N

I

bull

F IGURE 6 The country of Sweden with SIlaquoine and Blekinge counties enlarged The 17 municipalities ill the studies are numbered corresponding to Table II ie I Vellinge 2 Svedala 3 Skurup 4 Hbbr 5 Ystad 6 Trelleborg 76 Gbinge 8 6rkelljunga 9 Bromblla 10 Perstorp I I Klippan 12 Astorp 13 Kristianstad 14 Sirnrishamn 15 Angelholm 16 Karlskrona and 17 Karlshamn

drinking water (298-99mgL-) (Figure 7) This meansT AB LE II Number of Waterworks Range of that the ri sk of dying from M I was about 30 lowerMagnesium (Mg) Concentrations in Drinking Water compared with the risk for those who used drinking(mgL- ) and Amount of Mg in Water Supplied to the water with the lowest levels of magnesium (RubenowitzMost Densely Populated Areas (mgL-) et al 1996 1999)

A few years later a prospective interview study was Water Mg in the conducted in the same area where men and women who

Number of Range of most densely suffered from AM I from 1994 to 19 were compared Municipality waterworks water Mg populated area with population controls (Rllbenowitz et al 20(0) The no in the study (mgL-I) (mgL I) results showed that magnesium in drinking water proshy

tected against death from AM I but the total incidence 2 59-100 100 was not affected In particular the number of deaths

2 2 68-200 200 outside hospitals was lower in the quartile with high 3 4 26-100 90 fllelgnesiurn levels This supports the hypothesis that 4 2 88-130 88

magnesium prevents sudden death from ANI rather5 5 5 1-119 75

than all CHD deaths The mechanisms that could6 4 65-180 160 explain these findings are discllssed below 7 9 33-135 50

8 3 30-69 69

9 5 13-76 13 10 2 40-90 90 II 2 55-90 80 V PHYSIOLOGICAL IM PORTA N CE 12 100 100

OF MAGNESIUM13 15 13-144 67 14 9 38-134 97

15 2 70-110 110 A Physiological Properties of 16 9 20-130 20

Magnesium in Humans17 2 19-50 20

Municipality numbers correspond to Figure 6 11agnesium is involved in several important enzymatic reactions All reactions that involve ATP (adenosine triphosphate) thelt is energy demanding reactions have an absolute magnesium requirement (Reinhardt 1988)

339 VATER HARDNESS AND H EALTH EFFECTS

OR men5 ----------------------------------------------------

0 100 1088 TI to651070

I_I )

0 --------c----------------=--=------------J s35 36-68 69-97 ~98

mg2- (mg L- )

OR women 5r ------------------~----------------------------~

108 100 0

093

r 1 r

70

5

0 s34 s35-67 68-9 8 ~99 mg2+ (mg L- )

F IGURE 7 Odds ratios (OR) with 95 confidence intervals Jr death from AMI in relation to magnesium in drinking water ~dj usted for age and calcium) in men and women

il nportant processes in the body mediated by magneshyi UJ1l are for example synthesis of protein nucleic acid nL fat glucose use neuromuscular transmission musshy

-u lar contraction and transport over cell membranes ]tura amp Altura 1996) (see also Chapter 30 this o lulle)

lagnesium is essential to the cardiovascular system nd two properties are especially important stabilizing

ilie cardiac electric system (preventing cardiac arrhythshymia) and regulating vascular tone (Reinhardt 1991) T here are multiple mechanisms behind these properties

lagnesium is needed to maintain the normal gradishy~nr of potassium and calcium over cell membranes ltura et aI 1981) It is well known that magnesium is

necessary to maintain intracellular levels of potassium T his is done by blocking the outward passage of potasshy-i Ulll through the cell membrane and by activating the ecnzvme NaK-ATPase It has a similar function in CashylTPase Magnesium also has a direct effect on potasshyiUIll and calcium channels in the cell membranes Reinhardt 1991)

Furthermore as regards impact on vascular tone Ilugnesium is a necessary activator for the synthesis of

cyclic adenosine monophosphate (c-Ai1P) which is a vasodilator It also acts as a natural calcium antagonist by competing for calcium binding sites in the vascular smooth muscle and thus reducing the constrictive effect of calcium in the blood vessels (Reinhardt 1991) In addition the vasoconstrictive actions of hormones such as angiotensin serotonin and acetylcholine are enhanced in the case of magnesium deficiency (Alhua et al 1981)

VI M AGNESIUM INTAKE

A Magnesium Deficiency

Marginal magnesium deficiency probably affects a large proportion of the population whose dietary intake does not reach the recommended amount Although severe magnesium deficiency is not common in the population hypomagnesemia is often present among hospitalized patients (Altura 1994) A survey showed that hyposhylIlagnesemia was the most common electrolyte abnorshymality in patients entering the intensive care unit and was present in 20 of the patients (Reinhardt 1988) (see also Chapter 8 this volume)

The causes of hypomagnesemia include reduced intake caused by starvation or intravenous therapy without magnesium supplement impaired absorption owing to chronic diarrhea or malabsorption syndromes increased renal loss caused by diseases such as diabetes or renal diseases or by the use of alcohol or such drugs as diuretics or antibiotics (Reinhardt 1988)

B Magnesium Intake From Food

The largest part of the total magnesium intake is from foodstuffs Magnesium is present in many foodshlffs and in large amounts in nuts beans green leafy vegshyetables and whole grain cereals Mainly because of increased industrial treatment which decreases magneshysium levels by 80 to 95 (Marier 1986h) it has been suggested that the majority of people today have a lower magnesium intake than the recommended dietary amount (RDA) of 6 mg kg-I day-I (Marier 1986b Seelig 1986 Durlach 1989) Table III shows the magnesium content in some foodstuffs and beverages

Approximately 40 of magnesium ingested in food is normally absorbed (Hardwick et aL 1990) The proshyportion absorbed is inversely related to the amount ingested however and has been shown to range between approximately 10 and 70 (Fine et aL 1991)

340 VTER HARD-IESS A--D J-IMTII EFFECTS

TABLE II Magnesium (Mg) Content in Food and Beverages

Food items and Mg (mg Food items and Mg(mg beverages loog I) beverages fOOg- l

)

Food items Food items Bread white 23 Bananas 33 Bread fiber-rich 50 Fish 25 Muesli 100 Shrimp 42 Corn flakes 16 Meat 25 Cheese 34 Eggs 13 Common beans 184 Almonds 280

white dried Common beans 131 Peanuts 188

brown dried Corn 23 Dark chocolate 130 Spinach 79 Milk chocolate 60 Avocado 39 Broccoli 23 Beverages Tomato 10 Milk 12 Cucumber 10 Coffee 5 Mushrooms 13 Tea 3 Brown rice 110 Beer low alcohol 8

content White rice 34 Beer high alcohol II

content Potatoes 24 Red wine 12 Apples 5 White wine 3 Oranges 10 Spirits 0

Magnesium content in the water not included

The absorption rate also depends on the intake of other foodstuffs Elements such as calcium phosphorus fibers and phytic acids are known to diminish the absorption rate of magnesium (Seelig 1986) Most magnesium is absorbed in the distal small intestine mainly by passive diffusion through the panlCellubr pathway but also to a smaller extent by solvent drag and active transport (Hardwick et aI 1990)

VI I WAT E R MAGNESI U M AND

BODY MAGNES I U M STATUS

A Magnesium Intake From WatershyImportance for Body Magnesium Status

Vlagnesium has a natural source in water from the weathering of a range of rock types In igneous rock

magnesium is typically a constituent of the dark colored ferromagnesian minerals which include olivine pyroxshyenes ltlm phiboles and dark colored micas In altered rocks magnesian mineral species also occllr such 1S chlorite montmorillonite and serpentine Sedimentary forms of magnesium include magnesite (MgCO) and dolomite (CaiVIg(CO)) iVlagnesiulll is substantially less 1bunclant than calcium in all rock types and 0 in most natural waters the magnesium concentration is much lower usuall y by 5-10 times than the calciuIll concentration Concentrations of I11ltlgnesium in fresh waters are controlled by solution and precipitation reactions involving magnesiurn-bearing siJjcate and carbonate minerals with concentrations typically less than 50mgL-1

although values above IOOmgL I are recorded

Magnesium intake via water depends on the level in drinking water An important issue in discussions about the relation between vater magnesium and AMI is whether magnesium in drinking water can be critical for the body magnesiulll status as the main part of the magnes ium intake derives from food (Neutra 1999) It has been suggested th n the quantitative contribution of water magnesium may be crucial for body magnesium status for those who have a low dietary intake and use water with high magnesium levels (Durlach et aI 1989) L1 addition cooking food in magnesium-poor water leaches out magnesium while cooking in magnesiul1lshyrich water diminishes this loss (Haring amp 7a n Delft 1981)

Furthermore it has been suggested that magnesium in water appearing as hydrated ions has a higher bioavaila bility than magnesium in food which i bound ill different compounds that are less easily absorbed (Durbch et al 19H9 Theophanides et aI 1990) However simultaneous intake of other agents could diminish the absorption rate as discussed above

Plants cultivated in areas with magnesium-rich water may have higher magnesium content especially if the soil is magnesium-rich and the land is irrigated with magnesium-rich water People living in such areas who eat locally grown vegetables and fruits may also benefit from an addition to the total m1gnesium intake espeshycially during slimmer months H owever genetic factors appear to have a greater effect on plant magnesium composition than do soil and environmental factors (Vilkinson et aL 1987)

Some previous studies have shown relations between water magnesium and body magnesium content In a study of baboons tap water was more effective than dietary supplementation in increasing serum levels of magnesium and zinc (Robbins amp Sly 1981 ) Anderson

341 VATER HARDgtESS AKD HEALTH EFFE CTS

et 1 1 (1975) found relations between water magnesium md magnesium content in the hea rt muscle The m~ocardial ma gnesium was approximately 7 lower J l1ong residents of citi es with soft water T here lS however no difference in magnesium content in th e diaphragm or the pectoralis major muscle Other tudies have shown relations between water magnesium lecls and the magnesium content in skeletal ll1uscie and in coromllY lrteri es (Landin et aI 1989)

In a loading test 10 subjects who normally used water u ith a magnesium level of 16 mg L-I instead ve re given drinking wa ter with 20 I11g L - I magnesium Afte r six weeks of supplementation with l1lltlgnesium-enriched I lter the excretjon of magnesium wa s increased which indicated improved body magnesium status Ruhenmvitz et aI 1998)

nother study demonstrated that the ionized se rum magnesium level was rltlised after only six days of an increased di etltlry load of magnes ium but not the total hody magnesium However a correlation between ionized serum md ioni zed intracellular magnesium was 5hown (Altura amp Al tura 1996)

From the available data it is apparent that the quanshyriteltive contribution from water may be crll cial The m agnesiumlevcls in drinking water in the Swed ish caseshyontrol studies ranged from 0 to 44mgL- I Nith a tota l h ily intake of drinking water of two liters the proporshyjomll magnesium contribution from water thus ranges

from 0 to 88mgday- l This is a percentage contribution between 0 and 25 o f the RDA of 350mgday- l For those who hlVe 1 daily intake lower thaJ1 the RDA and m e magnesium-rich water the contribution would he (~ n more important

In the prospective study the calculated in take of lagnesium from food rell1ged from 15 7 to 658mgday-l

m edian 35 6mg day- I This means that a large number of the subjects had a lower intake than the RDA One gtubject with an intake of 157 mg magnesium per day used drinking water with 35mg L-l which mea ns a 15 addition to the magnesium intake from fo od If he instead had used water with 40 mg L - I the addishy

ti nn would have been 50 and the total daily intake ~-+o mg day- I

III C ALCIUM IN D RI N KI N G W ATER

N D CARDIOVASCULAR D ISEASE

T he majority of the previolls ecological studies showed 1n inverse rela tion hetween calcium in drinking water

and CVD 15 reported above The physio logical mechshy1l1isms thlt cou ld explain the reLltionship He not clear T here is hmveer evidence that calcium defici ency can cause hypertensi on vhich is a well-known risk factor for bo th stroke and A III (La u amp E by 1985 Vloore 1989 Vltl e lgter amp Brunner 1994)

A Calcium Deficiency

Calcium deficiency is common among the elde rl y espeshyci l lJy women The absorption nnd renal conscrvltl tion of calciu m decreases vith age The absorption of calcium from food varies between 15 and 75 (Schaafsma 1992) but in menolgtlt1l1sal wom en the absorption is only about 20- 30)) (Hemy amp Recker 1985) Furthermore cllciull1 intake is often decreased among the elderly (Harlan et aI 1984) The RDA for calcium in Sweden is 800 mg day- I for adult women and 600 mg day- I fo r men In the 1nited States the RDA is 1000-1 500 111g delyi for ad ults

stud ~ comprising 61000 women in Sweden e1 ged 40-76 showed that calcium intake decreased with age and thlt1t a majo rity of postmel1opausll women had a deficie nt calcium intake (1ichae lsson 1996) Several stud ies conducted in the United States have also shown an intake lower than recommended especially amo ng women (F leming amp Heimbach 1994) For individuals with a deficiency the additional cllciul1l fro lll water could be crucial to prevent this Along with the contrishybution of drin king water cooking food in Cltllcium-rich water has been shown not only to prevent lelching hut even to increlse ca lcium levels in rhe food (Ilaring amp van Delft 1981 )

B Calcium and Blood Pressure

Several studies have shown an inverse rebtion beteen dietary calciu111 in take and blood pressure fer3shyanalysis compri si ng l1early 40000 people ha s shown that a high calcium intake lowered both systo lic and diastolic hlood pressure (Cappucio et aI 1(95) Low serum concentrltl tions of ioni 7ed Gllcium have been me1sured in patien ts with hypertension ( IcCarron 1982) There are several possible 111 echlI1i sIllS that could expLlin how ca lcium lowers bl ood pressure

One mcchelllism 111lt1 y be that hypocalcemia inhihi ts C3-ATPlse activity which 1Clt1ds to an increase in fre e intracellular calci um and colltraction of vascubr smooth muscles (McCarron 198 5) Calcium supplementatio n has been shown to be efficaci ous especially among sa ltshy

VVATER HARD-ESS

unmimll1tly by geologiGll factors The geochemistry of rock weathering determines the release of elements into water In groundwaters a natural evolution of chemical composition is recognized Dilute rainwater with a odium chloride water type and contailling CO2 enters

e soil zone whereupon further CO2 produced by the Jecay of organic matter is dissolved in the inllltnlting middot Her to form carbonic acid vVithin the soil and Ul1satshyJrltlted zone of sedimentary rocks tbis weak acid disshyohes soluble calcium and magnesium carbonates such J calcite and dolomite to give high concentrations of alciul11 magnesium and bicarbonate In crystalline

~1l eous and metamorphic rocks slow wCltlthering of silshycd tes by the attack of carhonic acid releases low conshy

x lltrations of calcium magnesium potassium and i)diUlll in the infiltrating soil water or groundwater and h o produces bicarbonate

-way from the supply of oA)gen in the soil and unsatshyrated zone infiltrating water becomes increasingly noxic as a result of progressive bacterial recluction

oxygen Below the water table and with increasing _ducing conditions iron and manganese become

nhili zed and then later precipitated as metal sulfides the presence of disseminated clay material within an qui fer ion exchange replaces calcium for sodium as

e water evolves to a sodium bicarbonate water type lence the grounclwater is naturally softened by ion

hange reactions In the deeper confined section of ui fers mixing with saline water may occur to produce odiull1 chloride water type before a region of static Jtt r and aquifer dingenesis is reached Either pnrt or

o f this classic sequence of hydrochemical change Identified in a number of aquifers including the Iridl1l aquifer system The Floridan aquifer system occurs in the southeast ired States (Figure 2) and is one of the most proshy ti lmiddote aquifers in the world The aquifer system is a

_-ticaJly continuous sequence of Tertiary carbonate L~ of generally high permeability Limestones and lDlites are the principal rock types although in _~h I estcrn and northeastern Georgia and in South o]jna the limestones grade into lime-rich sands and _ The Florichl11 aquifer is composed primarily of ~ ~e mel dolomite with minor gypsum apatite glaushy

- middotrt quartz clay minerals and trace amounts of it oxides and suI fides

ThL total hardness of water in the U pper Floridan _r aries from lt50 to gt5000mgL- as CaCO JJJ~ where the system is composed only of Jimeshy

~ _ the total hardness is equivalent to carbonate ~lIld is ltl20mgL- I

Groundwater with higher -artiness usually results from (1) dissolution of

A-D HEALTH E PFE CTS 333

other aquifer minerals primarily dolomite and gypsum (2) mixing of fresh water with residual saline groundshywater (3) encroachment and mixing of modern seawashyter or (4) contamination Na tural softening of the groundwater hy cation exchange is thought to be responsible for the low hardness in Escambia and Santa Rosa Counties Florida (Sprinkle 1989)

A sequence of hydrochemical evolution is identified hy Sprinkle (1989) which start~ with calcite dissoluti on in recharge areas that produces a calcium-bicarhonate dominated water type with a total dissolved solids (TOS) concentration of generaLly less than 250 mg L- Oowngradient dissolution of dolomite leads to a calciul11-magnesium-bicarhonlte water type here gypsum is abundant sulfate becomes the predominant anion In coastal arens as shown in Figure 3 seawater increases the TDS concentration and the water type changes to sodium-chloride In the western panhandle of Florida cation exchange leads to the development of a sodium-bicarbonate water type and a less hard groundwater

For additional reading on groundwater modeling see Modeling Groundwater Flow and Quality this volume

III TH E HARD-WATER S TO RY

The history behind what is considered today to be a commonly accepted fact-that hard water protects against CVD-is often referrecl to as the hard-water story The hard-water story started in 1957 wjth Jun Kobayashi a Japanese ngricultural chemist He had for many years been engaged in studies of the nature oflrrishygation water from all agricultural point of view In these studies he fOLlnd a close relation between the chemical composition of river water and the death rate from apoplexy (CVD) The death rate of apoplexy inJapan was extraordinarily high compared to other counuies and the biggest cause of death in Japan Kobayashi found that it was the ratio of sulfur to calmiddotbonate (SOjCaO) that was related to the death rate fr0111 apoplexy He suggested that inorgmic acid CaCO might induce or prevent apoplex) (Kobayashi 1957)

Three years later a study was presented by Schroeder (1960) comprising the 163 largest cities in the United States I-Ie found inverse correlations between water hardness and CVD in both men and women He aLso studied the relation between different water conshystituents and coronary heart disease (CHD) 11TI0ng 45shyto ()4-year-old men He found significant correlations

334 iVATER I-L~RD~ESS AND HLLTH EFFECTS

South Carolina Georgia

Alabama

Total hardness of water (mgL as CaC03)

1-1 0-60 (Soft)

1222161-120 (Moderately hard)

tmtI121-180 (Hard)

~ gt180 (Very hard)

-____ Limit of reliable data

Groundwater well

o 100 km I I

88deg 86deg 84

FIGU R E 2 Map of the extent of the Upper Floridan Aquifer showing the spatial distribution of total hardness of water Escambia and Santa Rosa Counties Florida are located at pOSitions E and SR respectively (After Sprinkle 1989)

between death rate from CHD and sulfate and hicarshybonate respectively but not for the ratio of the agents He also found significant negative correlations between deaths from CHD and magnesium calcium fluoride and pH The coefficient of correlation for magnesium in drinking water was r = -030 P lt001 and for calcium r = -027 P lt00 I (Schroeder 1960)

During the following decades several sUldies on the relation betveen water hardness and CVD were preshysented Initially the studies dealt with the question of Ihether there was a toxic effect in soft water or a proshytective effect in hard water As described above soft aters usually have low buffering capacity and are more corrosive which leads to higher amounts of toxic trace elements It has been proposed that this could account for the observed increased mortality However the results from previous studies have not supported this

hypothesis (lVlarier 1986a) For example in a nationshywide survey of more than 500 tap waters in Canada no significant correlation was found between mortality and trace elements like lead cadmium cobalt lithium mercury molybdenum nickel or vanadium (Neri et al 1975) Gradually it became obvious that it was a proshytective effect from hard water that was responsible for the relations seen In different parts of the world studies have bccn made on the relation betccn magshynesium and calcium in the local drinking water and CVD mortality These studies were generally based upon death registers and water data at regional or municipality levels The results of d1ese smdies are sumshymarizcd in T1ble 1

Even with these studies the results were not conclushysive as to the role of magnesium and calcium in drinking water for CVD Most of the studies showed a relation

VATER I-LRDXESS

1000----------------------------------

100

shyJ)

-

Q 10 I-=shy

12 r--- ~ j u

Ic ---I--f-----~~-~middotgt V o

1 7 I II 1 ~+-J

01

001

I Crewsville1 t

I i

20

CIshy

I Na+

I 11

Mg2+

1 1 SO~- I1 1 Ca2

1 +

-HCo

Distance (km) 60 80 100 120I Fort Ogden I

Avon Park Lake June South Punta in Winter Gorda Heights

A A

F IGURE 3 Hydrochemical section along lineA-A (for locashy In see Figure 2) showing the variation in concentrations of 2jor ions downgradient in the direction of groundwater flow - ~Iative to calcium and magnesium the groundwater experishy=~es an increasing concentration of sodium as a result of ion Ex-change and mixing with saline water in the coastal zone ~fter Sprinkle 1989)

_bull middoteen different cardiovascular deaths and either magshy ~iU111 or calcium or bOtJl but some studies showed no -da tion at aiL However most of these studies were ecoshy

rieal meaning that the exposure to water constituents J- determined at group levels with a high risk of misshy

aJJS ification Often very large groups for example all habitants in large cities or arcas were assigned the lTIe ltllue of water magnesium and calcium despite the

icnce of several waterworks or private wells

AKD HEALTH EFFECTS 335

TABLE J The Effect of High Magnesium (Mg) or Calcium (Ca) Levels in Drinking Water on the Mortality from Cardiovascular Disease (CVD) Coronary Heart Disease (CHD) or Cerebrovascular Disease (CD) in Different Studies Published since 1975

Mg Co

Studies CVD CHD CD CVD CHD CD

North America Dawson et al 1978 J J Neri et aI 1975

Great Britain Shaper et aI 1980 Maheswaran et aI 1999

Germany Teitge 1990

Sweden Nerbrand et al 1992 Rylander et aI 1991

South Africa Leary et aI 1983

J

J

J

J J J J

J

t = lower mortality - = no difference

In addition the disease diagnoses studied were someshytimes unspecific with wide definitions that included both cardiac and cerebrovascular diseases In some studics it is also unclear whether the range of magneshysium and calcium in drinking water W 15 large enough to allow for appropriate analyses

One of tJle most comprehensive studies of the geoshygraphic variations in cardiovascular mortality was the British Regional Heart Study The first phase of this study (Pocock et aL 1980) applied multiple regression analysis to the geographical variations in CVD for men and women aged 35-74 in 253 urban areas in England Vales and Scotland from 1969 to 1973 The investishygation showed that the effect of water hardness was nonLinear much greater in the range from very soft to medium-hard water than from medium to very hard water The geometric mean for the standardized mortality ratio (SMR) for CVD for towns grouped according to water hardness both with and without adjustments (by analysis of covariance) for tJle effects of four climatic and socioeconomic variables (percentage of days WitJl rain mean daily maximum temperature pershy

336 VATER HARD-ESS A-D HEALTH EFF ECT S

-- Unadjusted

- - - Adjusted for climate and socio-economic conditions

120

110

a 2 (j) 100 c ro Cll 2

90

80

10 50 90 130 170 210 250 290 Water hardness (mg L-1 as CaC03)

47 33 22 14 19 20 43 36 Number of towns

FIGURE 4 Geometric means of the standardized mortality ratio (SMR) (for all men and women aged 35-74 with CVD) for

towns in England Wales and Scotland grouped according to water hardness (in concentration units of mg L middot1 as CaCO)

equivalent) (After Pocock et al 1980)

centage of manual workers car ownership) is shown in Figure 4 The adjusted SMR decreased steadily in moving from a hardness of 10 to 170 mg L - I but changed little between 170 to 290 mg L- or greater After adjustshyment CVD in areas with very soft water around 25 mg L-1

W )5 estimated to be 10-15 higher than in areas with medium-hard water around 170 mg L- I whereas any further increase in hardness heyond 170 mg L -I did not additionally lower CVD mortality Hence it appeared that the maximum effect on CVD WIS princishyP)lly between the very soft and medium-hard waters Adjusting for climatic and socioeconomic differences considerably reduced the apparent magniulde of the effect of water hlrdness (Pocock et al 1980)

A problem with correlation studies such as the British Regional Heart Study as argued by Jones and Moon (1987) is the t~lilure of much of the research to consider the causal mechanism that links independent variables to the disease outcome Also many of the calibrated models presented in tlle literature are socially blind in including only variables pertaining to the physical envishyronment which often contributes a large number of water qua Ii ty elements Even in those better analyses that have included social varilhles as in the case of the British Regional Heart Study the relatively strong corshyrelation found for calcium in England and Vales may be a result of calcium acting as a rery good surrogate for social variables The soft water areas of the north and west of the British Isles equate to tlle areas of early

100r-------------------------------------~

90 0 Suriyawewa

80 ~ Uda Walawe j( =395 mg L-1 as CaC03 (n =102)

~ Ridiyagama70i 60 u ~ 50 J

g 40 tt

30

20

10

O +-~~~~~~~-L~~~-L~~Lr~~~~

0-60 61-150 151-500 501 - 1000 gt1000

Total hardness (mg L -I as CaC03)

FIGURE 5 Histogram of total hardness values recorded for

groundwaters sampled during the wet season Uanuary and Febshyruary 200 I) from dug wells and tubewells in three subcatchments

of the Uda Walawe basin of Sri Lanka (Data courtesy of L Rajashysooriyar)

industrialization and today these areas house a disproshyportionate percentlge of the socially disadvantaged Gones amp Moon 1987) Therefore it is important thar further smdies undertake tlle challenge of quantitatively analyzing the seplrate effects of social variables fro111 those of water hardness

Fewer sUldies have been carried out in developing countries but Dissanayake et al (1982) for example found a negative correlation beveen water harclness and vlrious forms of CVD and leukemia in Sri Lanb N[ore recent sUldies (Dissanayake 1991 Rajasooriy~lr 2(03) have highlighted the problem of high fluoride concentrations and associated dental fluorosis in areas of hard water abstracted from crystalline bedrock aquifers in Sri Lanka

Rajasooriyar (2003) measured total hardness in dug vells and tubewelJs in the Uda vValawe basin of southern Sri Lanka in the wide range of7-3579mgL-1 as CaCO with an average of 395 mgL- as CaCO (Figure 5) Compared with the government water quality limit of 600 11lgL- as CaCO 12 ofthe 102 samples collected during tlle wet season in 2001 were in excesS of the limit and are considered too hard to drink (values above 100- 150mg-L-1 as CaCO j are 10cltllIy considered too hard as a water supply) Soft waters are found in are)s with a dense irrigation netvork supplied by rain-fed surface reservoirs Irrigation canal waters in the Suriyavewa and Ucla vValawe subcatchments were measshyured in the dry season to have a total hardness in the range 40-90mgL-1 as CaCO) (Rajasooriyar 2(03) and it is leakage of this water source that leads to tlle softenshy

337tVATpoundll HARDNESS AJD HEALT il EffECTS

ing ofshlllow grmmdwater The majority of the groundshywaters (63 ) in the fractured aqujfer represent very hard -lter with carb()l1ate hardness in the range 151- 500 mg L- ~s CaCO) contributed by the weathering of ferroshymagnesian minenJls anorthite calcite and dolomite T he products of this weathering lead to high concentrashytions of dissolved calcium magnesilllll and bicarbonate in gronndwaters E xceptionally high values of hardness gt 1O()OmgL - I as CaC03) typiCltl11y occur in non-irrishy

l tecl areas with additional non-carbonate hrrdness COllshy

rr ibuted by pyrite oxidation and in the case of the coastal Ri diyagam coastal catchment by salt water inputs

IV S TUDIES AT AN INDIVIDUAL LEVEL

In recent years some studies have been made with a igher precision as regards exposure classification than he previously cited ecological studies Most of them 3-e been conducted with a case-control design This

1I1S thlt the exposure to water magnesium and l icium has been estimated for i11dividuals who have uttered from the disease as well as for healthy control

-cr ons and the difference in risk calculated A simil lr Pc of study design is the prospective cohort study here the subjects are followed over time

Studies in Finland

lTI ltar and Karvonen 111lde a cohort study in 1979 I-te ~ compared the denh rate from CHI) in two rural

alt in vestern and eastern Finland The cohort -nprised men 40-59 years old in J 959 and they were ilOlred for 15 years The water data were not truly Ji-idual but were median volues in ten suhareas in the

[ern 1rea md 33 SUblleaS in the eastern area The ges of sUbltllmiddotel medians were 69- 27R I11g L - I of ter magnesium in the western area and O6- 73mgL-1

~he eastern area The cohort in eastern Finland had _ath rate hmiddotom CHD which was 1 7 times higher than

- estern cohort C alcium was not investigated few years Later Luoma et a (J983) published a

_ -control study conducted in the southeastern region - Fi nland Cases were men 30-04 year~ of age with

rt 1cute myocardial infarction (AMT alive or tlS t d) who were pair-matched with hospital conshy

fo r age and region (rmal vs urban) L1 addition ub tion controls vcre selected and matched for age m unjcipality All subjects submitted a sample of

their drinking water The range of magnesium in the drinking water was 10- 575 mgL- for the cases and 075-300mgL- and l0-160mgL- for the hospital controls and population controls respectively For caseshypopulation control comparisons the relative risk (RR) with 95deg) confidence limjts was 47 (9510 confidence interval [ell J3-253) for magnesiull1levels lower than l2 mgL - 1

bull This means that those with the lowest magshynesium levels had a risk of AiVil almost fi ve times higher than those with higher magnesium lerels For the caseshyhospital control comparisons the RR was 20 (95 CI 07- 65) that is double the risk They also found inverse relations vith fluoride levels but no relation to calcium

B Studies in Sweden

In Sweden three case-control studies have heen conshyducted during the last decade First using mortality registers the rebtion between death from AMI and the level of magnesium and calcium in drinking water was examined among men A few years later a study with a similar design WlS made comprising women The studies were conducted in southern Sweden in a relashytively small geographic area where there was a great difference between as well as within the municipalities regarding magnesium and calcium content in drinking w~lter The advantage with this lirnited study area was that the possible risk of such confounding factors as climate geographical cultural and socjoeconomic difshyferences was minimized

Seventeen municipalities were identified whose water quality vith respect to water hardness acidity and treatment procedures had been basically unchanged (change of hardness lt10 and pH lt5 ) during the most recent ten years Figure 6 shows the location of tbe 17 mUL1icipalities that comprised the study area

Cases vere men (n = 854) and women (n = 378) in 17 municipalities in southern Sweden who had died of AiVIJ between ages 50 and 69 years Controls were men (n =989) and women (n = 1368) of the same age group who had died of cancer LJdividnal water data were colshylected l~lhle II shows the number of vaterworks the range of magnesium in drinking water and the amount of magnesium in water supplied to the most densely populated area in each municipality

The subjects -were divided into quartiles according to

the levels of magnesium Odds ratios were calcula ted in relation to the group with the lowest exposure Adjustshyments for age were ll1ade in aU analyses The results show odds ratios of 065 for men and 070 for women in the quartile with highest magnesium levels in the

N

I

bull

F IGURE 6 The country of Sweden with SIlaquoine and Blekinge counties enlarged The 17 municipalities ill the studies are numbered corresponding to Table II ie I Vellinge 2 Svedala 3 Skurup 4 Hbbr 5 Ystad 6 Trelleborg 76 Gbinge 8 6rkelljunga 9 Bromblla 10 Perstorp I I Klippan 12 Astorp 13 Kristianstad 14 Sirnrishamn 15 Angelholm 16 Karlskrona and 17 Karlshamn

drinking water (298-99mgL-) (Figure 7) This meansT AB LE II Number of Waterworks Range of that the ri sk of dying from M I was about 30 lowerMagnesium (Mg) Concentrations in Drinking Water compared with the risk for those who used drinking(mgL- ) and Amount of Mg in Water Supplied to the water with the lowest levels of magnesium (RubenowitzMost Densely Populated Areas (mgL-) et al 1996 1999)

A few years later a prospective interview study was Water Mg in the conducted in the same area where men and women who

Number of Range of most densely suffered from AM I from 1994 to 19 were compared Municipality waterworks water Mg populated area with population controls (Rllbenowitz et al 20(0) The no in the study (mgL-I) (mgL I) results showed that magnesium in drinking water proshy

tected against death from AM I but the total incidence 2 59-100 100 was not affected In particular the number of deaths

2 2 68-200 200 outside hospitals was lower in the quartile with high 3 4 26-100 90 fllelgnesiurn levels This supports the hypothesis that 4 2 88-130 88

magnesium prevents sudden death from ANI rather5 5 5 1-119 75

than all CHD deaths The mechanisms that could6 4 65-180 160 explain these findings are discllssed below 7 9 33-135 50

8 3 30-69 69

9 5 13-76 13 10 2 40-90 90 II 2 55-90 80 V PHYSIOLOGICAL IM PORTA N CE 12 100 100

OF MAGNESIUM13 15 13-144 67 14 9 38-134 97

15 2 70-110 110 A Physiological Properties of 16 9 20-130 20

Magnesium in Humans17 2 19-50 20

Municipality numbers correspond to Figure 6 11agnesium is involved in several important enzymatic reactions All reactions that involve ATP (adenosine triphosphate) thelt is energy demanding reactions have an absolute magnesium requirement (Reinhardt 1988)

339 VATER HARDNESS AND H EALTH EFFECTS

OR men5 ----------------------------------------------------

0 100 1088 TI to651070

I_I )

0 --------c----------------=--=------------J s35 36-68 69-97 ~98

mg2- (mg L- )

OR women 5r ------------------~----------------------------~

108 100 0

093

r 1 r

70

5

0 s34 s35-67 68-9 8 ~99 mg2+ (mg L- )

F IGURE 7 Odds ratios (OR) with 95 confidence intervals Jr death from AMI in relation to magnesium in drinking water ~dj usted for age and calcium) in men and women

il nportant processes in the body mediated by magneshyi UJ1l are for example synthesis of protein nucleic acid nL fat glucose use neuromuscular transmission musshy

-u lar contraction and transport over cell membranes ]tura amp Altura 1996) (see also Chapter 30 this o lulle)

lagnesium is essential to the cardiovascular system nd two properties are especially important stabilizing

ilie cardiac electric system (preventing cardiac arrhythshymia) and regulating vascular tone (Reinhardt 1991) T here are multiple mechanisms behind these properties

lagnesium is needed to maintain the normal gradishy~nr of potassium and calcium over cell membranes ltura et aI 1981) It is well known that magnesium is

necessary to maintain intracellular levels of potassium T his is done by blocking the outward passage of potasshy-i Ulll through the cell membrane and by activating the ecnzvme NaK-ATPase It has a similar function in CashylTPase Magnesium also has a direct effect on potasshyiUIll and calcium channels in the cell membranes Reinhardt 1991)

Furthermore as regards impact on vascular tone Ilugnesium is a necessary activator for the synthesis of

cyclic adenosine monophosphate (c-Ai1P) which is a vasodilator It also acts as a natural calcium antagonist by competing for calcium binding sites in the vascular smooth muscle and thus reducing the constrictive effect of calcium in the blood vessels (Reinhardt 1991) In addition the vasoconstrictive actions of hormones such as angiotensin serotonin and acetylcholine are enhanced in the case of magnesium deficiency (Alhua et al 1981)

VI M AGNESIUM INTAKE

A Magnesium Deficiency

Marginal magnesium deficiency probably affects a large proportion of the population whose dietary intake does not reach the recommended amount Although severe magnesium deficiency is not common in the population hypomagnesemia is often present among hospitalized patients (Altura 1994) A survey showed that hyposhylIlagnesemia was the most common electrolyte abnorshymality in patients entering the intensive care unit and was present in 20 of the patients (Reinhardt 1988) (see also Chapter 8 this volume)

The causes of hypomagnesemia include reduced intake caused by starvation or intravenous therapy without magnesium supplement impaired absorption owing to chronic diarrhea or malabsorption syndromes increased renal loss caused by diseases such as diabetes or renal diseases or by the use of alcohol or such drugs as diuretics or antibiotics (Reinhardt 1988)

B Magnesium Intake From Food

The largest part of the total magnesium intake is from foodstuffs Magnesium is present in many foodshlffs and in large amounts in nuts beans green leafy vegshyetables and whole grain cereals Mainly because of increased industrial treatment which decreases magneshysium levels by 80 to 95 (Marier 1986h) it has been suggested that the majority of people today have a lower magnesium intake than the recommended dietary amount (RDA) of 6 mg kg-I day-I (Marier 1986b Seelig 1986 Durlach 1989) Table III shows the magnesium content in some foodstuffs and beverages

Approximately 40 of magnesium ingested in food is normally absorbed (Hardwick et aL 1990) The proshyportion absorbed is inversely related to the amount ingested however and has been shown to range between approximately 10 and 70 (Fine et aL 1991)

340 VTER HARD-IESS A--D J-IMTII EFFECTS

TABLE II Magnesium (Mg) Content in Food and Beverages

Food items and Mg (mg Food items and Mg(mg beverages loog I) beverages fOOg- l

)

Food items Food items Bread white 23 Bananas 33 Bread fiber-rich 50 Fish 25 Muesli 100 Shrimp 42 Corn flakes 16 Meat 25 Cheese 34 Eggs 13 Common beans 184 Almonds 280

white dried Common beans 131 Peanuts 188

brown dried Corn 23 Dark chocolate 130 Spinach 79 Milk chocolate 60 Avocado 39 Broccoli 23 Beverages Tomato 10 Milk 12 Cucumber 10 Coffee 5 Mushrooms 13 Tea 3 Brown rice 110 Beer low alcohol 8

content White rice 34 Beer high alcohol II

content Potatoes 24 Red wine 12 Apples 5 White wine 3 Oranges 10 Spirits 0

Magnesium content in the water not included

The absorption rate also depends on the intake of other foodstuffs Elements such as calcium phosphorus fibers and phytic acids are known to diminish the absorption rate of magnesium (Seelig 1986) Most magnesium is absorbed in the distal small intestine mainly by passive diffusion through the panlCellubr pathway but also to a smaller extent by solvent drag and active transport (Hardwick et aI 1990)

VI I WAT E R MAGNESI U M AND

BODY MAGNES I U M STATUS

A Magnesium Intake From WatershyImportance for Body Magnesium Status

Vlagnesium has a natural source in water from the weathering of a range of rock types In igneous rock

magnesium is typically a constituent of the dark colored ferromagnesian minerals which include olivine pyroxshyenes ltlm phiboles and dark colored micas In altered rocks magnesian mineral species also occllr such 1S chlorite montmorillonite and serpentine Sedimentary forms of magnesium include magnesite (MgCO) and dolomite (CaiVIg(CO)) iVlagnesiulll is substantially less 1bunclant than calcium in all rock types and 0 in most natural waters the magnesium concentration is much lower usuall y by 5-10 times than the calciuIll concentration Concentrations of I11ltlgnesium in fresh waters are controlled by solution and precipitation reactions involving magnesiurn-bearing siJjcate and carbonate minerals with concentrations typically less than 50mgL-1

although values above IOOmgL I are recorded

Magnesium intake via water depends on the level in drinking water An important issue in discussions about the relation between vater magnesium and AMI is whether magnesium in drinking water can be critical for the body magnesiulll status as the main part of the magnes ium intake derives from food (Neutra 1999) It has been suggested th n the quantitative contribution of water magnesium may be crucial for body magnesium status for those who have a low dietary intake and use water with high magnesium levels (Durlach et aI 1989) L1 addition cooking food in magnesium-poor water leaches out magnesium while cooking in magnesiul1lshyrich water diminishes this loss (Haring amp 7a n Delft 1981)

Furthermore it has been suggested that magnesium in water appearing as hydrated ions has a higher bioavaila bility than magnesium in food which i bound ill different compounds that are less easily absorbed (Durbch et al 19H9 Theophanides et aI 1990) However simultaneous intake of other agents could diminish the absorption rate as discussed above

Plants cultivated in areas with magnesium-rich water may have higher magnesium content especially if the soil is magnesium-rich and the land is irrigated with magnesium-rich water People living in such areas who eat locally grown vegetables and fruits may also benefit from an addition to the total m1gnesium intake espeshycially during slimmer months H owever genetic factors appear to have a greater effect on plant magnesium composition than do soil and environmental factors (Vilkinson et aL 1987)

Some previous studies have shown relations between water magnesium and body magnesium content In a study of baboons tap water was more effective than dietary supplementation in increasing serum levels of magnesium and zinc (Robbins amp Sly 1981 ) Anderson

341 VATER HARDgtESS AKD HEALTH EFFE CTS

et 1 1 (1975) found relations between water magnesium md magnesium content in the hea rt muscle The m~ocardial ma gnesium was approximately 7 lower J l1ong residents of citi es with soft water T here lS however no difference in magnesium content in th e diaphragm or the pectoralis major muscle Other tudies have shown relations between water magnesium lecls and the magnesium content in skeletal ll1uscie and in coromllY lrteri es (Landin et aI 1989)

In a loading test 10 subjects who normally used water u ith a magnesium level of 16 mg L-I instead ve re given drinking wa ter with 20 I11g L - I magnesium Afte r six weeks of supplementation with l1lltlgnesium-enriched I lter the excretjon of magnesium wa s increased which indicated improved body magnesium status Ruhenmvitz et aI 1998)

nother study demonstrated that the ionized se rum magnesium level was rltlised after only six days of an increased di etltlry load of magnes ium but not the total hody magnesium However a correlation between ionized serum md ioni zed intracellular magnesium was 5hown (Altura amp Al tura 1996)

From the available data it is apparent that the quanshyriteltive contribution from water may be crll cial The m agnesiumlevcls in drinking water in the Swed ish caseshyontrol studies ranged from 0 to 44mgL- I Nith a tota l h ily intake of drinking water of two liters the proporshyjomll magnesium contribution from water thus ranges

from 0 to 88mgday- l This is a percentage contribution between 0 and 25 o f the RDA of 350mgday- l For those who hlVe 1 daily intake lower thaJ1 the RDA and m e magnesium-rich water the contribution would he (~ n more important

In the prospective study the calculated in take of lagnesium from food rell1ged from 15 7 to 658mgday-l

m edian 35 6mg day- I This means that a large number of the subjects had a lower intake than the RDA One gtubject with an intake of 157 mg magnesium per day used drinking water with 35mg L-l which mea ns a 15 addition to the magnesium intake from fo od If he instead had used water with 40 mg L - I the addishy

ti nn would have been 50 and the total daily intake ~-+o mg day- I

III C ALCIUM IN D RI N KI N G W ATER

N D CARDIOVASCULAR D ISEASE

T he majority of the previolls ecological studies showed 1n inverse rela tion hetween calcium in drinking water

and CVD 15 reported above The physio logical mechshy1l1isms thlt cou ld explain the reLltionship He not clear T here is hmveer evidence that calcium defici ency can cause hypertensi on vhich is a well-known risk factor for bo th stroke and A III (La u amp E by 1985 Vloore 1989 Vltl e lgter amp Brunner 1994)

A Calcium Deficiency

Calcium deficiency is common among the elde rl y espeshyci l lJy women The absorption nnd renal conscrvltl tion of calciu m decreases vith age The absorption of calcium from food varies between 15 and 75 (Schaafsma 1992) but in menolgtlt1l1sal wom en the absorption is only about 20- 30)) (Hemy amp Recker 1985) Furthermore cllciull1 intake is often decreased among the elderly (Harlan et aI 1984) The RDA for calcium in Sweden is 800 mg day- I for adult women and 600 mg day- I fo r men In the 1nited States the RDA is 1000-1 500 111g delyi for ad ults

stud ~ comprising 61000 women in Sweden e1 ged 40-76 showed that calcium intake decreased with age and thlt1t a majo rity of postmel1opausll women had a deficie nt calcium intake (1ichae lsson 1996) Several stud ies conducted in the United States have also shown an intake lower than recommended especially amo ng women (F leming amp Heimbach 1994) For individuals with a deficiency the additional cllciul1l fro lll water could be crucial to prevent this Along with the contrishybution of drin king water cooking food in Cltllcium-rich water has been shown not only to prevent lelching hut even to increlse ca lcium levels in rhe food (Ilaring amp van Delft 1981 )

B Calcium and Blood Pressure

Several studies have shown an inverse rebtion beteen dietary calciu111 in take and blood pressure fer3shyanalysis compri si ng l1early 40000 people ha s shown that a high calcium intake lowered both systo lic and diastolic hlood pressure (Cappucio et aI 1(95) Low serum concentrltl tions of ioni 7ed Gllcium have been me1sured in patien ts with hypertension ( IcCarron 1982) There are several possible 111 echlI1i sIllS that could expLlin how ca lcium lowers bl ood pressure

One mcchelllism 111lt1 y be that hypocalcemia inhihi ts C3-ATPlse activity which 1Clt1ds to an increase in fre e intracellular calci um and colltraction of vascubr smooth muscles (McCarron 198 5) Calcium supplementatio n has been shown to be efficaci ous especially among sa ltshy

334 iVATER I-L~RD~ESS AND HLLTH EFFECTS

South Carolina Georgia

Alabama

Total hardness of water (mgL as CaC03)

1-1 0-60 (Soft)

1222161-120 (Moderately hard)

tmtI121-180 (Hard)

~ gt180 (Very hard)

-____ Limit of reliable data

Groundwater well

o 100 km I I

88deg 86deg 84

FIGU R E 2 Map of the extent of the Upper Floridan Aquifer showing the spatial distribution of total hardness of water Escambia and Santa Rosa Counties Florida are located at pOSitions E and SR respectively (After Sprinkle 1989)

between death rate from CHD and sulfate and hicarshybonate respectively but not for the ratio of the agents He also found significant negative correlations between deaths from CHD and magnesium calcium fluoride and pH The coefficient of correlation for magnesium in drinking water was r = -030 P lt001 and for calcium r = -027 P lt00 I (Schroeder 1960)

During the following decades several sUldies on the relation betveen water hardness and CVD were preshysented Initially the studies dealt with the question of Ihether there was a toxic effect in soft water or a proshytective effect in hard water As described above soft aters usually have low buffering capacity and are more corrosive which leads to higher amounts of toxic trace elements It has been proposed that this could account for the observed increased mortality However the results from previous studies have not supported this

hypothesis (lVlarier 1986a) For example in a nationshywide survey of more than 500 tap waters in Canada no significant correlation was found between mortality and trace elements like lead cadmium cobalt lithium mercury molybdenum nickel or vanadium (Neri et al 1975) Gradually it became obvious that it was a proshytective effect from hard water that was responsible for the relations seen In different parts of the world studies have bccn made on the relation betccn magshynesium and calcium in the local drinking water and CVD mortality These studies were generally based upon death registers and water data at regional or municipality levels The results of d1ese smdies are sumshymarizcd in T1ble 1

Even with these studies the results were not conclushysive as to the role of magnesium and calcium in drinking water for CVD Most of the studies showed a relation

VATER I-LRDXESS

1000----------------------------------

100

shyJ)

-

Q 10 I-=shy

12 r--- ~ j u

Ic ---I--f-----~~-~middotgt V o

1 7 I II 1 ~+-J

01

001

I Crewsville1 t

I i

20

CIshy

I Na+

I 11

Mg2+

1 1 SO~- I1 1 Ca2

1 +

-HCo

Distance (km) 60 80 100 120I Fort Ogden I

Avon Park Lake June South Punta in Winter Gorda Heights

A A

F IGURE 3 Hydrochemical section along lineA-A (for locashy In see Figure 2) showing the variation in concentrations of 2jor ions downgradient in the direction of groundwater flow - ~Iative to calcium and magnesium the groundwater experishy=~es an increasing concentration of sodium as a result of ion Ex-change and mixing with saline water in the coastal zone ~fter Sprinkle 1989)

_bull middoteen different cardiovascular deaths and either magshy ~iU111 or calcium or bOtJl but some studies showed no -da tion at aiL However most of these studies were ecoshy

rieal meaning that the exposure to water constituents J- determined at group levels with a high risk of misshy

aJJS ification Often very large groups for example all habitants in large cities or arcas were assigned the lTIe ltllue of water magnesium and calcium despite the

icnce of several waterworks or private wells

AKD HEALTH EFFECTS 335

TABLE J The Effect of High Magnesium (Mg) or Calcium (Ca) Levels in Drinking Water on the Mortality from Cardiovascular Disease (CVD) Coronary Heart Disease (CHD) or Cerebrovascular Disease (CD) in Different Studies Published since 1975

Mg Co

Studies CVD CHD CD CVD CHD CD

North America Dawson et al 1978 J J Neri et aI 1975

Great Britain Shaper et aI 1980 Maheswaran et aI 1999

Germany Teitge 1990

Sweden Nerbrand et al 1992 Rylander et aI 1991

South Africa Leary et aI 1983

J

J

J

J J J J

J

t = lower mortality - = no difference

In addition the disease diagnoses studied were someshytimes unspecific with wide definitions that included both cardiac and cerebrovascular diseases In some studics it is also unclear whether the range of magneshysium and calcium in drinking water W 15 large enough to allow for appropriate analyses

One of tJle most comprehensive studies of the geoshygraphic variations in cardiovascular mortality was the British Regional Heart Study The first phase of this study (Pocock et aL 1980) applied multiple regression analysis to the geographical variations in CVD for men and women aged 35-74 in 253 urban areas in England Vales and Scotland from 1969 to 1973 The investishygation showed that the effect of water hardness was nonLinear much greater in the range from very soft to medium-hard water than from medium to very hard water The geometric mean for the standardized mortality ratio (SMR) for CVD for towns grouped according to water hardness both with and without adjustments (by analysis of covariance) for tJle effects of four climatic and socioeconomic variables (percentage of days WitJl rain mean daily maximum temperature pershy

336 VATER HARD-ESS A-D HEALTH EFF ECT S

-- Unadjusted

- - - Adjusted for climate and socio-economic conditions

120

110

a 2 (j) 100 c ro Cll 2

90

80

10 50 90 130 170 210 250 290 Water hardness (mg L-1 as CaC03)

47 33 22 14 19 20 43 36 Number of towns

FIGURE 4 Geometric means of the standardized mortality ratio (SMR) (for all men and women aged 35-74 with CVD) for

towns in England Wales and Scotland grouped according to water hardness (in concentration units of mg L middot1 as CaCO)

equivalent) (After Pocock et al 1980)

centage of manual workers car ownership) is shown in Figure 4 The adjusted SMR decreased steadily in moving from a hardness of 10 to 170 mg L - I but changed little between 170 to 290 mg L- or greater After adjustshyment CVD in areas with very soft water around 25 mg L-1

W )5 estimated to be 10-15 higher than in areas with medium-hard water around 170 mg L- I whereas any further increase in hardness heyond 170 mg L -I did not additionally lower CVD mortality Hence it appeared that the maximum effect on CVD WIS princishyP)lly between the very soft and medium-hard waters Adjusting for climatic and socioeconomic differences considerably reduced the apparent magniulde of the effect of water hlrdness (Pocock et al 1980)

A problem with correlation studies such as the British Regional Heart Study as argued by Jones and Moon (1987) is the t~lilure of much of the research to consider the causal mechanism that links independent variables to the disease outcome Also many of the calibrated models presented in tlle literature are socially blind in including only variables pertaining to the physical envishyronment which often contributes a large number of water qua Ii ty elements Even in those better analyses that have included social varilhles as in the case of the British Regional Heart Study the relatively strong corshyrelation found for calcium in England and Vales may be a result of calcium acting as a rery good surrogate for social variables The soft water areas of the north and west of the British Isles equate to tlle areas of early

100r-------------------------------------~

90 0 Suriyawewa

80 ~ Uda Walawe j( =395 mg L-1 as CaC03 (n =102)

~ Ridiyagama70i 60 u ~ 50 J

g 40 tt

30

20

10

O +-~~~~~~~-L~~~-L~~Lr~~~~

0-60 61-150 151-500 501 - 1000 gt1000

Total hardness (mg L -I as CaC03)

FIGURE 5 Histogram of total hardness values recorded for

groundwaters sampled during the wet season Uanuary and Febshyruary 200 I) from dug wells and tubewells in three subcatchments

of the Uda Walawe basin of Sri Lanka (Data courtesy of L Rajashysooriyar)

industrialization and today these areas house a disproshyportionate percentlge of the socially disadvantaged Gones amp Moon 1987) Therefore it is important thar further smdies undertake tlle challenge of quantitatively analyzing the seplrate effects of social variables fro111 those of water hardness

Fewer sUldies have been carried out in developing countries but Dissanayake et al (1982) for example found a negative correlation beveen water harclness and vlrious forms of CVD and leukemia in Sri Lanb N[ore recent sUldies (Dissanayake 1991 Rajasooriy~lr 2(03) have highlighted the problem of high fluoride concentrations and associated dental fluorosis in areas of hard water abstracted from crystalline bedrock aquifers in Sri Lanka

Rajasooriyar (2003) measured total hardness in dug vells and tubewelJs in the Uda vValawe basin of southern Sri Lanka in the wide range of7-3579mgL-1 as CaCO with an average of 395 mgL- as CaCO (Figure 5) Compared with the government water quality limit of 600 11lgL- as CaCO 12 ofthe 102 samples collected during tlle wet season in 2001 were in excesS of the limit and are considered too hard to drink (values above 100- 150mg-L-1 as CaCO j are 10cltllIy considered too hard as a water supply) Soft waters are found in are)s with a dense irrigation netvork supplied by rain-fed surface reservoirs Irrigation canal waters in the Suriyavewa and Ucla vValawe subcatchments were measshyured in the dry season to have a total hardness in the range 40-90mgL-1 as CaCO) (Rajasooriyar 2(03) and it is leakage of this water source that leads to tlle softenshy

337tVATpoundll HARDNESS AJD HEALT il EffECTS

ing ofshlllow grmmdwater The majority of the groundshywaters (63 ) in the fractured aqujfer represent very hard -lter with carb()l1ate hardness in the range 151- 500 mg L- ~s CaCO) contributed by the weathering of ferroshymagnesian minenJls anorthite calcite and dolomite T he products of this weathering lead to high concentrashytions of dissolved calcium magnesilllll and bicarbonate in gronndwaters E xceptionally high values of hardness gt 1O()OmgL - I as CaC03) typiCltl11y occur in non-irrishy

l tecl areas with additional non-carbonate hrrdness COllshy

rr ibuted by pyrite oxidation and in the case of the coastal Ri diyagam coastal catchment by salt water inputs

IV S TUDIES AT AN INDIVIDUAL LEVEL

In recent years some studies have been made with a igher precision as regards exposure classification than he previously cited ecological studies Most of them 3-e been conducted with a case-control design This

1I1S thlt the exposure to water magnesium and l icium has been estimated for i11dividuals who have uttered from the disease as well as for healthy control

-cr ons and the difference in risk calculated A simil lr Pc of study design is the prospective cohort study here the subjects are followed over time

Studies in Finland

lTI ltar and Karvonen 111lde a cohort study in 1979 I-te ~ compared the denh rate from CHI) in two rural

alt in vestern and eastern Finland The cohort -nprised men 40-59 years old in J 959 and they were ilOlred for 15 years The water data were not truly Ji-idual but were median volues in ten suhareas in the

[ern 1rea md 33 SUblleaS in the eastern area The ges of sUbltllmiddotel medians were 69- 27R I11g L - I of ter magnesium in the western area and O6- 73mgL-1

~he eastern area The cohort in eastern Finland had _ath rate hmiddotom CHD which was 1 7 times higher than

- estern cohort C alcium was not investigated few years Later Luoma et a (J983) published a

_ -control study conducted in the southeastern region - Fi nland Cases were men 30-04 year~ of age with

rt 1cute myocardial infarction (AMT alive or tlS t d) who were pair-matched with hospital conshy

fo r age and region (rmal vs urban) L1 addition ub tion controls vcre selected and matched for age m unjcipality All subjects submitted a sample of

their drinking water The range of magnesium in the drinking water was 10- 575 mgL- for the cases and 075-300mgL- and l0-160mgL- for the hospital controls and population controls respectively For caseshypopulation control comparisons the relative risk (RR) with 95deg) confidence limjts was 47 (9510 confidence interval [ell J3-253) for magnesiull1levels lower than l2 mgL - 1

bull This means that those with the lowest magshynesium levels had a risk of AiVil almost fi ve times higher than those with higher magnesium lerels For the caseshyhospital control comparisons the RR was 20 (95 CI 07- 65) that is double the risk They also found inverse relations vith fluoride levels but no relation to calcium

B Studies in Sweden

In Sweden three case-control studies have heen conshyducted during the last decade First using mortality registers the rebtion between death from AMI and the level of magnesium and calcium in drinking water was examined among men A few years later a study with a similar design WlS made comprising women The studies were conducted in southern Sweden in a relashytively small geographic area where there was a great difference between as well as within the municipalities regarding magnesium and calcium content in drinking w~lter The advantage with this lirnited study area was that the possible risk of such confounding factors as climate geographical cultural and socjoeconomic difshyferences was minimized

Seventeen municipalities were identified whose water quality vith respect to water hardness acidity and treatment procedures had been basically unchanged (change of hardness lt10 and pH lt5 ) during the most recent ten years Figure 6 shows the location of tbe 17 mUL1icipalities that comprised the study area

Cases vere men (n = 854) and women (n = 378) in 17 municipalities in southern Sweden who had died of AiVIJ between ages 50 and 69 years Controls were men (n =989) and women (n = 1368) of the same age group who had died of cancer LJdividnal water data were colshylected l~lhle II shows the number of vaterworks the range of magnesium in drinking water and the amount of magnesium in water supplied to the most densely populated area in each municipality

The subjects -were divided into quartiles according to

the levels of magnesium Odds ratios were calcula ted in relation to the group with the lowest exposure Adjustshyments for age were ll1ade in aU analyses The results show odds ratios of 065 for men and 070 for women in the quartile with highest magnesium levels in the

N

I

bull

F IGURE 6 The country of Sweden with SIlaquoine and Blekinge counties enlarged The 17 municipalities ill the studies are numbered corresponding to Table II ie I Vellinge 2 Svedala 3 Skurup 4 Hbbr 5 Ystad 6 Trelleborg 76 Gbinge 8 6rkelljunga 9 Bromblla 10 Perstorp I I Klippan 12 Astorp 13 Kristianstad 14 Sirnrishamn 15 Angelholm 16 Karlskrona and 17 Karlshamn

drinking water (298-99mgL-) (Figure 7) This meansT AB LE II Number of Waterworks Range of that the ri sk of dying from M I was about 30 lowerMagnesium (Mg) Concentrations in Drinking Water compared with the risk for those who used drinking(mgL- ) and Amount of Mg in Water Supplied to the water with the lowest levels of magnesium (RubenowitzMost Densely Populated Areas (mgL-) et al 1996 1999)

A few years later a prospective interview study was Water Mg in the conducted in the same area where men and women who

Number of Range of most densely suffered from AM I from 1994 to 19 were compared Municipality waterworks water Mg populated area with population controls (Rllbenowitz et al 20(0) The no in the study (mgL-I) (mgL I) results showed that magnesium in drinking water proshy

tected against death from AM I but the total incidence 2 59-100 100 was not affected In particular the number of deaths

2 2 68-200 200 outside hospitals was lower in the quartile with high 3 4 26-100 90 fllelgnesiurn levels This supports the hypothesis that 4 2 88-130 88

magnesium prevents sudden death from ANI rather5 5 5 1-119 75

than all CHD deaths The mechanisms that could6 4 65-180 160 explain these findings are discllssed below 7 9 33-135 50

8 3 30-69 69

9 5 13-76 13 10 2 40-90 90 II 2 55-90 80 V PHYSIOLOGICAL IM PORTA N CE 12 100 100

OF MAGNESIUM13 15 13-144 67 14 9 38-134 97

15 2 70-110 110 A Physiological Properties of 16 9 20-130 20

Magnesium in Humans17 2 19-50 20

Municipality numbers correspond to Figure 6 11agnesium is involved in several important enzymatic reactions All reactions that involve ATP (adenosine triphosphate) thelt is energy demanding reactions have an absolute magnesium requirement (Reinhardt 1988)

339 VATER HARDNESS AND H EALTH EFFECTS

OR men5 ----------------------------------------------------

0 100 1088 TI to651070

I_I )

0 --------c----------------=--=------------J s35 36-68 69-97 ~98

mg2- (mg L- )

OR women 5r ------------------~----------------------------~

108 100 0

093

r 1 r

70

5

0 s34 s35-67 68-9 8 ~99 mg2+ (mg L- )

F IGURE 7 Odds ratios (OR) with 95 confidence intervals Jr death from AMI in relation to magnesium in drinking water ~dj usted for age and calcium) in men and women

il nportant processes in the body mediated by magneshyi UJ1l are for example synthesis of protein nucleic acid nL fat glucose use neuromuscular transmission musshy

-u lar contraction and transport over cell membranes ]tura amp Altura 1996) (see also Chapter 30 this o lulle)

lagnesium is essential to the cardiovascular system nd two properties are especially important stabilizing

ilie cardiac electric system (preventing cardiac arrhythshymia) and regulating vascular tone (Reinhardt 1991) T here are multiple mechanisms behind these properties

lagnesium is needed to maintain the normal gradishy~nr of potassium and calcium over cell membranes ltura et aI 1981) It is well known that magnesium is

necessary to maintain intracellular levels of potassium T his is done by blocking the outward passage of potasshy-i Ulll through the cell membrane and by activating the ecnzvme NaK-ATPase It has a similar function in CashylTPase Magnesium also has a direct effect on potasshyiUIll and calcium channels in the cell membranes Reinhardt 1991)

Furthermore as regards impact on vascular tone Ilugnesium is a necessary activator for the synthesis of

cyclic adenosine monophosphate (c-Ai1P) which is a vasodilator It also acts as a natural calcium antagonist by competing for calcium binding sites in the vascular smooth muscle and thus reducing the constrictive effect of calcium in the blood vessels (Reinhardt 1991) In addition the vasoconstrictive actions of hormones such as angiotensin serotonin and acetylcholine are enhanced in the case of magnesium deficiency (Alhua et al 1981)

VI M AGNESIUM INTAKE

A Magnesium Deficiency

Marginal magnesium deficiency probably affects a large proportion of the population whose dietary intake does not reach the recommended amount Although severe magnesium deficiency is not common in the population hypomagnesemia is often present among hospitalized patients (Altura 1994) A survey showed that hyposhylIlagnesemia was the most common electrolyte abnorshymality in patients entering the intensive care unit and was present in 20 of the patients (Reinhardt 1988) (see also Chapter 8 this volume)

The causes of hypomagnesemia include reduced intake caused by starvation or intravenous therapy without magnesium supplement impaired absorption owing to chronic diarrhea or malabsorption syndromes increased renal loss caused by diseases such as diabetes or renal diseases or by the use of alcohol or such drugs as diuretics or antibiotics (Reinhardt 1988)

B Magnesium Intake From Food

The largest part of the total magnesium intake is from foodstuffs Magnesium is present in many foodshlffs and in large amounts in nuts beans green leafy vegshyetables and whole grain cereals Mainly because of increased industrial treatment which decreases magneshysium levels by 80 to 95 (Marier 1986h) it has been suggested that the majority of people today have a lower magnesium intake than the recommended dietary amount (RDA) of 6 mg kg-I day-I (Marier 1986b Seelig 1986 Durlach 1989) Table III shows the magnesium content in some foodstuffs and beverages

Approximately 40 of magnesium ingested in food is normally absorbed (Hardwick et aL 1990) The proshyportion absorbed is inversely related to the amount ingested however and has been shown to range between approximately 10 and 70 (Fine et aL 1991)

340 VTER HARD-IESS A--D J-IMTII EFFECTS

TABLE II Magnesium (Mg) Content in Food and Beverages

Food items and Mg (mg Food items and Mg(mg beverages loog I) beverages fOOg- l

)

Food items Food items Bread white 23 Bananas 33 Bread fiber-rich 50 Fish 25 Muesli 100 Shrimp 42 Corn flakes 16 Meat 25 Cheese 34 Eggs 13 Common beans 184 Almonds 280

white dried Common beans 131 Peanuts 188

brown dried Corn 23 Dark chocolate 130 Spinach 79 Milk chocolate 60 Avocado 39 Broccoli 23 Beverages Tomato 10 Milk 12 Cucumber 10 Coffee 5 Mushrooms 13 Tea 3 Brown rice 110 Beer low alcohol 8

content White rice 34 Beer high alcohol II

content Potatoes 24 Red wine 12 Apples 5 White wine 3 Oranges 10 Spirits 0

Magnesium content in the water not included

The absorption rate also depends on the intake of other foodstuffs Elements such as calcium phosphorus fibers and phytic acids are known to diminish the absorption rate of magnesium (Seelig 1986) Most magnesium is absorbed in the distal small intestine mainly by passive diffusion through the panlCellubr pathway but also to a smaller extent by solvent drag and active transport (Hardwick et aI 1990)

VI I WAT E R MAGNESI U M AND

BODY MAGNES I U M STATUS

A Magnesium Intake From WatershyImportance for Body Magnesium Status

Vlagnesium has a natural source in water from the weathering of a range of rock types In igneous rock

magnesium is typically a constituent of the dark colored ferromagnesian minerals which include olivine pyroxshyenes ltlm phiboles and dark colored micas In altered rocks magnesian mineral species also occllr such 1S chlorite montmorillonite and serpentine Sedimentary forms of magnesium include magnesite (MgCO) and dolomite (CaiVIg(CO)) iVlagnesiulll is substantially less 1bunclant than calcium in all rock types and 0 in most natural waters the magnesium concentration is much lower usuall y by 5-10 times than the calciuIll concentration Concentrations of I11ltlgnesium in fresh waters are controlled by solution and precipitation reactions involving magnesiurn-bearing siJjcate and carbonate minerals with concentrations typically less than 50mgL-1

although values above IOOmgL I are recorded

Magnesium intake via water depends on the level in drinking water An important issue in discussions about the relation between vater magnesium and AMI is whether magnesium in drinking water can be critical for the body magnesiulll status as the main part of the magnes ium intake derives from food (Neutra 1999) It has been suggested th n the quantitative contribution of water magnesium may be crucial for body magnesium status for those who have a low dietary intake and use water with high magnesium levels (Durlach et aI 1989) L1 addition cooking food in magnesium-poor water leaches out magnesium while cooking in magnesiul1lshyrich water diminishes this loss (Haring amp 7a n Delft 1981)

Furthermore it has been suggested that magnesium in water appearing as hydrated ions has a higher bioavaila bility than magnesium in food which i bound ill different compounds that are less easily absorbed (Durbch et al 19H9 Theophanides et aI 1990) However simultaneous intake of other agents could diminish the absorption rate as discussed above

Plants cultivated in areas with magnesium-rich water may have higher magnesium content especially if the soil is magnesium-rich and the land is irrigated with magnesium-rich water People living in such areas who eat locally grown vegetables and fruits may also benefit from an addition to the total m1gnesium intake espeshycially during slimmer months H owever genetic factors appear to have a greater effect on plant magnesium composition than do soil and environmental factors (Vilkinson et aL 1987)

Some previous studies have shown relations between water magnesium and body magnesium content In a study of baboons tap water was more effective than dietary supplementation in increasing serum levels of magnesium and zinc (Robbins amp Sly 1981 ) Anderson

341 VATER HARDgtESS AKD HEALTH EFFE CTS

et 1 1 (1975) found relations between water magnesium md magnesium content in the hea rt muscle The m~ocardial ma gnesium was approximately 7 lower J l1ong residents of citi es with soft water T here lS however no difference in magnesium content in th e diaphragm or the pectoralis major muscle Other tudies have shown relations between water magnesium lecls and the magnesium content in skeletal ll1uscie and in coromllY lrteri es (Landin et aI 1989)

In a loading test 10 subjects who normally used water u ith a magnesium level of 16 mg L-I instead ve re given drinking wa ter with 20 I11g L - I magnesium Afte r six weeks of supplementation with l1lltlgnesium-enriched I lter the excretjon of magnesium wa s increased which indicated improved body magnesium status Ruhenmvitz et aI 1998)

nother study demonstrated that the ionized se rum magnesium level was rltlised after only six days of an increased di etltlry load of magnes ium but not the total hody magnesium However a correlation between ionized serum md ioni zed intracellular magnesium was 5hown (Altura amp Al tura 1996)

From the available data it is apparent that the quanshyriteltive contribution from water may be crll cial The m agnesiumlevcls in drinking water in the Swed ish caseshyontrol studies ranged from 0 to 44mgL- I Nith a tota l h ily intake of drinking water of two liters the proporshyjomll magnesium contribution from water thus ranges

from 0 to 88mgday- l This is a percentage contribution between 0 and 25 o f the RDA of 350mgday- l For those who hlVe 1 daily intake lower thaJ1 the RDA and m e magnesium-rich water the contribution would he (~ n more important

In the prospective study the calculated in take of lagnesium from food rell1ged from 15 7 to 658mgday-l

m edian 35 6mg day- I This means that a large number of the subjects had a lower intake than the RDA One gtubject with an intake of 157 mg magnesium per day used drinking water with 35mg L-l which mea ns a 15 addition to the magnesium intake from fo od If he instead had used water with 40 mg L - I the addishy

ti nn would have been 50 and the total daily intake ~-+o mg day- I

III C ALCIUM IN D RI N KI N G W ATER

N D CARDIOVASCULAR D ISEASE

T he majority of the previolls ecological studies showed 1n inverse rela tion hetween calcium in drinking water

and CVD 15 reported above The physio logical mechshy1l1isms thlt cou ld explain the reLltionship He not clear T here is hmveer evidence that calcium defici ency can cause hypertensi on vhich is a well-known risk factor for bo th stroke and A III (La u amp E by 1985 Vloore 1989 Vltl e lgter amp Brunner 1994)

A Calcium Deficiency

Calcium deficiency is common among the elde rl y espeshyci l lJy women The absorption nnd renal conscrvltl tion of calciu m decreases vith age The absorption of calcium from food varies between 15 and 75 (Schaafsma 1992) but in menolgtlt1l1sal wom en the absorption is only about 20- 30)) (Hemy amp Recker 1985) Furthermore cllciull1 intake is often decreased among the elderly (Harlan et aI 1984) The RDA for calcium in Sweden is 800 mg day- I for adult women and 600 mg day- I fo r men In the 1nited States the RDA is 1000-1 500 111g delyi for ad ults

stud ~ comprising 61000 women in Sweden e1 ged 40-76 showed that calcium intake decreased with age and thlt1t a majo rity of postmel1opausll women had a deficie nt calcium intake (1ichae lsson 1996) Several stud ies conducted in the United States have also shown an intake lower than recommended especially amo ng women (F leming amp Heimbach 1994) For individuals with a deficiency the additional cllciul1l fro lll water could be crucial to prevent this Along with the contrishybution of drin king water cooking food in Cltllcium-rich water has been shown not only to prevent lelching hut even to increlse ca lcium levels in rhe food (Ilaring amp van Delft 1981 )

B Calcium and Blood Pressure

Several studies have shown an inverse rebtion beteen dietary calciu111 in take and blood pressure fer3shyanalysis compri si ng l1early 40000 people ha s shown that a high calcium intake lowered both systo lic and diastolic hlood pressure (Cappucio et aI 1(95) Low serum concentrltl tions of ioni 7ed Gllcium have been me1sured in patien ts with hypertension ( IcCarron 1982) There are several possible 111 echlI1i sIllS that could expLlin how ca lcium lowers bl ood pressure

One mcchelllism 111lt1 y be that hypocalcemia inhihi ts C3-ATPlse activity which 1Clt1ds to an increase in fre e intracellular calci um and colltraction of vascubr smooth muscles (McCarron 198 5) Calcium supplementatio n has been shown to be efficaci ous especially among sa ltshy

VATER I-LRDXESS

1000----------------------------------

100

shyJ)

-

Q 10 I-=shy

12 r--- ~ j u

Ic ---I--f-----~~-~middotgt V o

1 7 I II 1 ~+-J

01

001

I Crewsville1 t

I i

20

CIshy

I Na+

I 11

Mg2+

1 1 SO~- I1 1 Ca2

1 +

-HCo

Distance (km) 60 80 100 120I Fort Ogden I

Avon Park Lake June South Punta in Winter Gorda Heights

A A

F IGURE 3 Hydrochemical section along lineA-A (for locashy In see Figure 2) showing the variation in concentrations of 2jor ions downgradient in the direction of groundwater flow - ~Iative to calcium and magnesium the groundwater experishy=~es an increasing concentration of sodium as a result of ion Ex-change and mixing with saline water in the coastal zone ~fter Sprinkle 1989)

_bull middoteen different cardiovascular deaths and either magshy ~iU111 or calcium or bOtJl but some studies showed no -da tion at aiL However most of these studies were ecoshy

rieal meaning that the exposure to water constituents J- determined at group levels with a high risk of misshy

aJJS ification Often very large groups for example all habitants in large cities or arcas were assigned the lTIe ltllue of water magnesium and calcium despite the

icnce of several waterworks or private wells

AKD HEALTH EFFECTS 335

TABLE J The Effect of High Magnesium (Mg) or Calcium (Ca) Levels in Drinking Water on the Mortality from Cardiovascular Disease (CVD) Coronary Heart Disease (CHD) or Cerebrovascular Disease (CD) in Different Studies Published since 1975

Mg Co

Studies CVD CHD CD CVD CHD CD

North America Dawson et al 1978 J J Neri et aI 1975

Great Britain Shaper et aI 1980 Maheswaran et aI 1999

Germany Teitge 1990

Sweden Nerbrand et al 1992 Rylander et aI 1991

South Africa Leary et aI 1983

J

J

J

J J J J

J

t = lower mortality - = no difference

In addition the disease diagnoses studied were someshytimes unspecific with wide definitions that included both cardiac and cerebrovascular diseases In some studics it is also unclear whether the range of magneshysium and calcium in drinking water W 15 large enough to allow for appropriate analyses

One of tJle most comprehensive studies of the geoshygraphic variations in cardiovascular mortality was the British Regional Heart Study The first phase of this study (Pocock et aL 1980) applied multiple regression analysis to the geographical variations in CVD for men and women aged 35-74 in 253 urban areas in England Vales and Scotland from 1969 to 1973 The investishygation showed that the effect of water hardness was nonLinear much greater in the range from very soft to medium-hard water than from medium to very hard water The geometric mean for the standardized mortality ratio (SMR) for CVD for towns grouped according to water hardness both with and without adjustments (by analysis of covariance) for tJle effects of four climatic and socioeconomic variables (percentage of days WitJl rain mean daily maximum temperature pershy

336 VATER HARD-ESS A-D HEALTH EFF ECT S

-- Unadjusted

- - - Adjusted for climate and socio-economic conditions

120

110

a 2 (j) 100 c ro Cll 2

90

80

10 50 90 130 170 210 250 290 Water hardness (mg L-1 as CaC03)

47 33 22 14 19 20 43 36 Number of towns

FIGURE 4 Geometric means of the standardized mortality ratio (SMR) (for all men and women aged 35-74 with CVD) for

towns in England Wales and Scotland grouped according to water hardness (in concentration units of mg L middot1 as CaCO)

equivalent) (After Pocock et al 1980)

centage of manual workers car ownership) is shown in Figure 4 The adjusted SMR decreased steadily in moving from a hardness of 10 to 170 mg L - I but changed little between 170 to 290 mg L- or greater After adjustshyment CVD in areas with very soft water around 25 mg L-1

W )5 estimated to be 10-15 higher than in areas with medium-hard water around 170 mg L- I whereas any further increase in hardness heyond 170 mg L -I did not additionally lower CVD mortality Hence it appeared that the maximum effect on CVD WIS princishyP)lly between the very soft and medium-hard waters Adjusting for climatic and socioeconomic differences considerably reduced the apparent magniulde of the effect of water hlrdness (Pocock et al 1980)

A problem with correlation studies such as the British Regional Heart Study as argued by Jones and Moon (1987) is the t~lilure of much of the research to consider the causal mechanism that links independent variables to the disease outcome Also many of the calibrated models presented in tlle literature are socially blind in including only variables pertaining to the physical envishyronment which often contributes a large number of water qua Ii ty elements Even in those better analyses that have included social varilhles as in the case of the British Regional Heart Study the relatively strong corshyrelation found for calcium in England and Vales may be a result of calcium acting as a rery good surrogate for social variables The soft water areas of the north and west of the British Isles equate to tlle areas of early

100r-------------------------------------~

90 0 Suriyawewa

80 ~ Uda Walawe j( =395 mg L-1 as CaC03 (n =102)

~ Ridiyagama70i 60 u ~ 50 J

g 40 tt

30

20

10

O +-~~~~~~~-L~~~-L~~Lr~~~~

0-60 61-150 151-500 501 - 1000 gt1000

Total hardness (mg L -I as CaC03)

FIGURE 5 Histogram of total hardness values recorded for

groundwaters sampled during the wet season Uanuary and Febshyruary 200 I) from dug wells and tubewells in three subcatchments

of the Uda Walawe basin of Sri Lanka (Data courtesy of L Rajashysooriyar)

industrialization and today these areas house a disproshyportionate percentlge of the socially disadvantaged Gones amp Moon 1987) Therefore it is important thar further smdies undertake tlle challenge of quantitatively analyzing the seplrate effects of social variables fro111 those of water hardness

Fewer sUldies have been carried out in developing countries but Dissanayake et al (1982) for example found a negative correlation beveen water harclness and vlrious forms of CVD and leukemia in Sri Lanb N[ore recent sUldies (Dissanayake 1991 Rajasooriy~lr 2(03) have highlighted the problem of high fluoride concentrations and associated dental fluorosis in areas of hard water abstracted from crystalline bedrock aquifers in Sri Lanka

Rajasooriyar (2003) measured total hardness in dug vells and tubewelJs in the Uda vValawe basin of southern Sri Lanka in the wide range of7-3579mgL-1 as CaCO with an average of 395 mgL- as CaCO (Figure 5) Compared with the government water quality limit of 600 11lgL- as CaCO 12 ofthe 102 samples collected during tlle wet season in 2001 were in excesS of the limit and are considered too hard to drink (values above 100- 150mg-L-1 as CaCO j are 10cltllIy considered too hard as a water supply) Soft waters are found in are)s with a dense irrigation netvork supplied by rain-fed surface reservoirs Irrigation canal waters in the Suriyavewa and Ucla vValawe subcatchments were measshyured in the dry season to have a total hardness in the range 40-90mgL-1 as CaCO) (Rajasooriyar 2(03) and it is leakage of this water source that leads to tlle softenshy

337tVATpoundll HARDNESS AJD HEALT il EffECTS

ing ofshlllow grmmdwater The majority of the groundshywaters (63 ) in the fractured aqujfer represent very hard -lter with carb()l1ate hardness in the range 151- 500 mg L- ~s CaCO) contributed by the weathering of ferroshymagnesian minenJls anorthite calcite and dolomite T he products of this weathering lead to high concentrashytions of dissolved calcium magnesilllll and bicarbonate in gronndwaters E xceptionally high values of hardness gt 1O()OmgL - I as CaC03) typiCltl11y occur in non-irrishy

l tecl areas with additional non-carbonate hrrdness COllshy

rr ibuted by pyrite oxidation and in the case of the coastal Ri diyagam coastal catchment by salt water inputs

IV S TUDIES AT AN INDIVIDUAL LEVEL

In recent years some studies have been made with a igher precision as regards exposure classification than he previously cited ecological studies Most of them 3-e been conducted with a case-control design This

1I1S thlt the exposure to water magnesium and l icium has been estimated for i11dividuals who have uttered from the disease as well as for healthy control

-cr ons and the difference in risk calculated A simil lr Pc of study design is the prospective cohort study here the subjects are followed over time

Studies in Finland

lTI ltar and Karvonen 111lde a cohort study in 1979 I-te ~ compared the denh rate from CHI) in two rural

alt in vestern and eastern Finland The cohort -nprised men 40-59 years old in J 959 and they were ilOlred for 15 years The water data were not truly Ji-idual but were median volues in ten suhareas in the

[ern 1rea md 33 SUblleaS in the eastern area The ges of sUbltllmiddotel medians were 69- 27R I11g L - I of ter magnesium in the western area and O6- 73mgL-1

~he eastern area The cohort in eastern Finland had _ath rate hmiddotom CHD which was 1 7 times higher than

- estern cohort C alcium was not investigated few years Later Luoma et a (J983) published a

_ -control study conducted in the southeastern region - Fi nland Cases were men 30-04 year~ of age with

rt 1cute myocardial infarction (AMT alive or tlS t d) who were pair-matched with hospital conshy

fo r age and region (rmal vs urban) L1 addition ub tion controls vcre selected and matched for age m unjcipality All subjects submitted a sample of

their drinking water The range of magnesium in the drinking water was 10- 575 mgL- for the cases and 075-300mgL- and l0-160mgL- for the hospital controls and population controls respectively For caseshypopulation control comparisons the relative risk (RR) with 95deg) confidence limjts was 47 (9510 confidence interval [ell J3-253) for magnesiull1levels lower than l2 mgL - 1

bull This means that those with the lowest magshynesium levels had a risk of AiVil almost fi ve times higher than those with higher magnesium lerels For the caseshyhospital control comparisons the RR was 20 (95 CI 07- 65) that is double the risk They also found inverse relations vith fluoride levels but no relation to calcium

B Studies in Sweden

In Sweden three case-control studies have heen conshyducted during the last decade First using mortality registers the rebtion between death from AMI and the level of magnesium and calcium in drinking water was examined among men A few years later a study with a similar design WlS made comprising women The studies were conducted in southern Sweden in a relashytively small geographic area where there was a great difference between as well as within the municipalities regarding magnesium and calcium content in drinking w~lter The advantage with this lirnited study area was that the possible risk of such confounding factors as climate geographical cultural and socjoeconomic difshyferences was minimized

Seventeen municipalities were identified whose water quality vith respect to water hardness acidity and treatment procedures had been basically unchanged (change of hardness lt10 and pH lt5 ) during the most recent ten years Figure 6 shows the location of tbe 17 mUL1icipalities that comprised the study area

Cases vere men (n = 854) and women (n = 378) in 17 municipalities in southern Sweden who had died of AiVIJ between ages 50 and 69 years Controls were men (n =989) and women (n = 1368) of the same age group who had died of cancer LJdividnal water data were colshylected l~lhle II shows the number of vaterworks the range of magnesium in drinking water and the amount of magnesium in water supplied to the most densely populated area in each municipality

The subjects -were divided into quartiles according to

the levels of magnesium Odds ratios were calcula ted in relation to the group with the lowest exposure Adjustshyments for age were ll1ade in aU analyses The results show odds ratios of 065 for men and 070 for women in the quartile with highest magnesium levels in the

N

I

bull

F IGURE 6 The country of Sweden with SIlaquoine and Blekinge counties enlarged The 17 municipalities ill the studies are numbered corresponding to Table II ie I Vellinge 2 Svedala 3 Skurup 4 Hbbr 5 Ystad 6 Trelleborg 76 Gbinge 8 6rkelljunga 9 Bromblla 10 Perstorp I I Klippan 12 Astorp 13 Kristianstad 14 Sirnrishamn 15 Angelholm 16 Karlskrona and 17 Karlshamn

drinking water (298-99mgL-) (Figure 7) This meansT AB LE II Number of Waterworks Range of that the ri sk of dying from M I was about 30 lowerMagnesium (Mg) Concentrations in Drinking Water compared with the risk for those who used drinking(mgL- ) and Amount of Mg in Water Supplied to the water with the lowest levels of magnesium (RubenowitzMost Densely Populated Areas (mgL-) et al 1996 1999)

A few years later a prospective interview study was Water Mg in the conducted in the same area where men and women who

Number of Range of most densely suffered from AM I from 1994 to 19 were compared Municipality waterworks water Mg populated area with population controls (Rllbenowitz et al 20(0) The no in the study (mgL-I) (mgL I) results showed that magnesium in drinking water proshy

tected against death from AM I but the total incidence 2 59-100 100 was not affected In particular the number of deaths

2 2 68-200 200 outside hospitals was lower in the quartile with high 3 4 26-100 90 fllelgnesiurn levels This supports the hypothesis that 4 2 88-130 88

magnesium prevents sudden death from ANI rather5 5 5 1-119 75

than all CHD deaths The mechanisms that could6 4 65-180 160 explain these findings are discllssed below 7 9 33-135 50

8 3 30-69 69

9 5 13-76 13 10 2 40-90 90 II 2 55-90 80 V PHYSIOLOGICAL IM PORTA N CE 12 100 100

OF MAGNESIUM13 15 13-144 67 14 9 38-134 97

15 2 70-110 110 A Physiological Properties of 16 9 20-130 20

Magnesium in Humans17 2 19-50 20

Municipality numbers correspond to Figure 6 11agnesium is involved in several important enzymatic reactions All reactions that involve ATP (adenosine triphosphate) thelt is energy demanding reactions have an absolute magnesium requirement (Reinhardt 1988)

339 VATER HARDNESS AND H EALTH EFFECTS

OR men5 ----------------------------------------------------

0 100 1088 TI to651070

I_I )

0 --------c----------------=--=------------J s35 36-68 69-97 ~98

mg2- (mg L- )

OR women 5r ------------------~----------------------------~

108 100 0

093

r 1 r

70

5

0 s34 s35-67 68-9 8 ~99 mg2+ (mg L- )

F IGURE 7 Odds ratios (OR) with 95 confidence intervals Jr death from AMI in relation to magnesium in drinking water ~dj usted for age and calcium) in men and women

il nportant processes in the body mediated by magneshyi UJ1l are for example synthesis of protein nucleic acid nL fat glucose use neuromuscular transmission musshy

-u lar contraction and transport over cell membranes ]tura amp Altura 1996) (see also Chapter 30 this o lulle)

lagnesium is essential to the cardiovascular system nd two properties are especially important stabilizing

ilie cardiac electric system (preventing cardiac arrhythshymia) and regulating vascular tone (Reinhardt 1991) T here are multiple mechanisms behind these properties

lagnesium is needed to maintain the normal gradishy~nr of potassium and calcium over cell membranes ltura et aI 1981) It is well known that magnesium is

necessary to maintain intracellular levels of potassium T his is done by blocking the outward passage of potasshy-i Ulll through the cell membrane and by activating the ecnzvme NaK-ATPase It has a similar function in CashylTPase Magnesium also has a direct effect on potasshyiUIll and calcium channels in the cell membranes Reinhardt 1991)

Furthermore as regards impact on vascular tone Ilugnesium is a necessary activator for the synthesis of

cyclic adenosine monophosphate (c-Ai1P) which is a vasodilator It also acts as a natural calcium antagonist by competing for calcium binding sites in the vascular smooth muscle and thus reducing the constrictive effect of calcium in the blood vessels (Reinhardt 1991) In addition the vasoconstrictive actions of hormones such as angiotensin serotonin and acetylcholine are enhanced in the case of magnesium deficiency (Alhua et al 1981)

VI M AGNESIUM INTAKE

A Magnesium Deficiency

Marginal magnesium deficiency probably affects a large proportion of the population whose dietary intake does not reach the recommended amount Although severe magnesium deficiency is not common in the population hypomagnesemia is often present among hospitalized patients (Altura 1994) A survey showed that hyposhylIlagnesemia was the most common electrolyte abnorshymality in patients entering the intensive care unit and was present in 20 of the patients (Reinhardt 1988) (see also Chapter 8 this volume)

The causes of hypomagnesemia include reduced intake caused by starvation or intravenous therapy without magnesium supplement impaired absorption owing to chronic diarrhea or malabsorption syndromes increased renal loss caused by diseases such as diabetes or renal diseases or by the use of alcohol or such drugs as diuretics or antibiotics (Reinhardt 1988)

B Magnesium Intake From Food

The largest part of the total magnesium intake is from foodstuffs Magnesium is present in many foodshlffs and in large amounts in nuts beans green leafy vegshyetables and whole grain cereals Mainly because of increased industrial treatment which decreases magneshysium levels by 80 to 95 (Marier 1986h) it has been suggested that the majority of people today have a lower magnesium intake than the recommended dietary amount (RDA) of 6 mg kg-I day-I (Marier 1986b Seelig 1986 Durlach 1989) Table III shows the magnesium content in some foodstuffs and beverages

Approximately 40 of magnesium ingested in food is normally absorbed (Hardwick et aL 1990) The proshyportion absorbed is inversely related to the amount ingested however and has been shown to range between approximately 10 and 70 (Fine et aL 1991)

340 VTER HARD-IESS A--D J-IMTII EFFECTS

TABLE II Magnesium (Mg) Content in Food and Beverages

Food items and Mg (mg Food items and Mg(mg beverages loog I) beverages fOOg- l

)

Food items Food items Bread white 23 Bananas 33 Bread fiber-rich 50 Fish 25 Muesli 100 Shrimp 42 Corn flakes 16 Meat 25 Cheese 34 Eggs 13 Common beans 184 Almonds 280

white dried Common beans 131 Peanuts 188

brown dried Corn 23 Dark chocolate 130 Spinach 79 Milk chocolate 60 Avocado 39 Broccoli 23 Beverages Tomato 10 Milk 12 Cucumber 10 Coffee 5 Mushrooms 13 Tea 3 Brown rice 110 Beer low alcohol 8

content White rice 34 Beer high alcohol II

content Potatoes 24 Red wine 12 Apples 5 White wine 3 Oranges 10 Spirits 0

Magnesium content in the water not included

The absorption rate also depends on the intake of other foodstuffs Elements such as calcium phosphorus fibers and phytic acids are known to diminish the absorption rate of magnesium (Seelig 1986) Most magnesium is absorbed in the distal small intestine mainly by passive diffusion through the panlCellubr pathway but also to a smaller extent by solvent drag and active transport (Hardwick et aI 1990)

VI I WAT E R MAGNESI U M AND

BODY MAGNES I U M STATUS

A Magnesium Intake From WatershyImportance for Body Magnesium Status

Vlagnesium has a natural source in water from the weathering of a range of rock types In igneous rock

magnesium is typically a constituent of the dark colored ferromagnesian minerals which include olivine pyroxshyenes ltlm phiboles and dark colored micas In altered rocks magnesian mineral species also occllr such 1S chlorite montmorillonite and serpentine Sedimentary forms of magnesium include magnesite (MgCO) and dolomite (CaiVIg(CO)) iVlagnesiulll is substantially less 1bunclant than calcium in all rock types and 0 in most natural waters the magnesium concentration is much lower usuall y by 5-10 times than the calciuIll concentration Concentrations of I11ltlgnesium in fresh waters are controlled by solution and precipitation reactions involving magnesiurn-bearing siJjcate and carbonate minerals with concentrations typically less than 50mgL-1

although values above IOOmgL I are recorded

Magnesium intake via water depends on the level in drinking water An important issue in discussions about the relation between vater magnesium and AMI is whether magnesium in drinking water can be critical for the body magnesiulll status as the main part of the magnes ium intake derives from food (Neutra 1999) It has been suggested th n the quantitative contribution of water magnesium may be crucial for body magnesium status for those who have a low dietary intake and use water with high magnesium levels (Durlach et aI 1989) L1 addition cooking food in magnesium-poor water leaches out magnesium while cooking in magnesiul1lshyrich water diminishes this loss (Haring amp 7a n Delft 1981)

Furthermore it has been suggested that magnesium in water appearing as hydrated ions has a higher bioavaila bility than magnesium in food which i bound ill different compounds that are less easily absorbed (Durbch et al 19H9 Theophanides et aI 1990) However simultaneous intake of other agents could diminish the absorption rate as discussed above

Plants cultivated in areas with magnesium-rich water may have higher magnesium content especially if the soil is magnesium-rich and the land is irrigated with magnesium-rich water People living in such areas who eat locally grown vegetables and fruits may also benefit from an addition to the total m1gnesium intake espeshycially during slimmer months H owever genetic factors appear to have a greater effect on plant magnesium composition than do soil and environmental factors (Vilkinson et aL 1987)

Some previous studies have shown relations between water magnesium and body magnesium content In a study of baboons tap water was more effective than dietary supplementation in increasing serum levels of magnesium and zinc (Robbins amp Sly 1981 ) Anderson

341 VATER HARDgtESS AKD HEALTH EFFE CTS

et 1 1 (1975) found relations between water magnesium md magnesium content in the hea rt muscle The m~ocardial ma gnesium was approximately 7 lower J l1ong residents of citi es with soft water T here lS however no difference in magnesium content in th e diaphragm or the pectoralis major muscle Other tudies have shown relations between water magnesium lecls and the magnesium content in skeletal ll1uscie and in coromllY lrteri es (Landin et aI 1989)

In a loading test 10 subjects who normally used water u ith a magnesium level of 16 mg L-I instead ve re given drinking wa ter with 20 I11g L - I magnesium Afte r six weeks of supplementation with l1lltlgnesium-enriched I lter the excretjon of magnesium wa s increased which indicated improved body magnesium status Ruhenmvitz et aI 1998)

nother study demonstrated that the ionized se rum magnesium level was rltlised after only six days of an increased di etltlry load of magnes ium but not the total hody magnesium However a correlation between ionized serum md ioni zed intracellular magnesium was 5hown (Altura amp Al tura 1996)

From the available data it is apparent that the quanshyriteltive contribution from water may be crll cial The m agnesiumlevcls in drinking water in the Swed ish caseshyontrol studies ranged from 0 to 44mgL- I Nith a tota l h ily intake of drinking water of two liters the proporshyjomll magnesium contribution from water thus ranges

from 0 to 88mgday- l This is a percentage contribution between 0 and 25 o f the RDA of 350mgday- l For those who hlVe 1 daily intake lower thaJ1 the RDA and m e magnesium-rich water the contribution would he (~ n more important

In the prospective study the calculated in take of lagnesium from food rell1ged from 15 7 to 658mgday-l

m edian 35 6mg day- I This means that a large number of the subjects had a lower intake than the RDA One gtubject with an intake of 157 mg magnesium per day used drinking water with 35mg L-l which mea ns a 15 addition to the magnesium intake from fo od If he instead had used water with 40 mg L - I the addishy

ti nn would have been 50 and the total daily intake ~-+o mg day- I

III C ALCIUM IN D RI N KI N G W ATER

N D CARDIOVASCULAR D ISEASE

T he majority of the previolls ecological studies showed 1n inverse rela tion hetween calcium in drinking water

and CVD 15 reported above The physio logical mechshy1l1isms thlt cou ld explain the reLltionship He not clear T here is hmveer evidence that calcium defici ency can cause hypertensi on vhich is a well-known risk factor for bo th stroke and A III (La u amp E by 1985 Vloore 1989 Vltl e lgter amp Brunner 1994)

A Calcium Deficiency

Calcium deficiency is common among the elde rl y espeshyci l lJy women The absorption nnd renal conscrvltl tion of calciu m decreases vith age The absorption of calcium from food varies between 15 and 75 (Schaafsma 1992) but in menolgtlt1l1sal wom en the absorption is only about 20- 30)) (Hemy amp Recker 1985) Furthermore cllciull1 intake is often decreased among the elderly (Harlan et aI 1984) The RDA for calcium in Sweden is 800 mg day- I for adult women and 600 mg day- I fo r men In the 1nited States the RDA is 1000-1 500 111g delyi for ad ults

stud ~ comprising 61000 women in Sweden e1 ged 40-76 showed that calcium intake decreased with age and thlt1t a majo rity of postmel1opausll women had a deficie nt calcium intake (1ichae lsson 1996) Several stud ies conducted in the United States have also shown an intake lower than recommended especially amo ng women (F leming amp Heimbach 1994) For individuals with a deficiency the additional cllciul1l fro lll water could be crucial to prevent this Along with the contrishybution of drin king water cooking food in Cltllcium-rich water has been shown not only to prevent lelching hut even to increlse ca lcium levels in rhe food (Ilaring amp van Delft 1981 )

B Calcium and Blood Pressure

Several studies have shown an inverse rebtion beteen dietary calciu111 in take and blood pressure fer3shyanalysis compri si ng l1early 40000 people ha s shown that a high calcium intake lowered both systo lic and diastolic hlood pressure (Cappucio et aI 1(95) Low serum concentrltl tions of ioni 7ed Gllcium have been me1sured in patien ts with hypertension ( IcCarron 1982) There are several possible 111 echlI1i sIllS that could expLlin how ca lcium lowers bl ood pressure

One mcchelllism 111lt1 y be that hypocalcemia inhihi ts C3-ATPlse activity which 1Clt1ds to an increase in fre e intracellular calci um and colltraction of vascubr smooth muscles (McCarron 198 5) Calcium supplementatio n has been shown to be efficaci ous especially among sa ltshy

336 VATER HARD-ESS A-D HEALTH EFF ECT S

-- Unadjusted

- - - Adjusted for climate and socio-economic conditions

120

110

a 2 (j) 100 c ro Cll 2

90

80

10 50 90 130 170 210 250 290 Water hardness (mg L-1 as CaC03)

47 33 22 14 19 20 43 36 Number of towns

FIGURE 4 Geometric means of the standardized mortality ratio (SMR) (for all men and women aged 35-74 with CVD) for

towns in England Wales and Scotland grouped according to water hardness (in concentration units of mg L middot1 as CaCO)

equivalent) (After Pocock et al 1980)

centage of manual workers car ownership) is shown in Figure 4 The adjusted SMR decreased steadily in moving from a hardness of 10 to 170 mg L - I but changed little between 170 to 290 mg L- or greater After adjustshyment CVD in areas with very soft water around 25 mg L-1

W )5 estimated to be 10-15 higher than in areas with medium-hard water around 170 mg L- I whereas any further increase in hardness heyond 170 mg L -I did not additionally lower CVD mortality Hence it appeared that the maximum effect on CVD WIS princishyP)lly between the very soft and medium-hard waters Adjusting for climatic and socioeconomic differences considerably reduced the apparent magniulde of the effect of water hlrdness (Pocock et al 1980)

A problem with correlation studies such as the British Regional Heart Study as argued by Jones and Moon (1987) is the t~lilure of much of the research to consider the causal mechanism that links independent variables to the disease outcome Also many of the calibrated models presented in tlle literature are socially blind in including only variables pertaining to the physical envishyronment which often contributes a large number of water qua Ii ty elements Even in those better analyses that have included social varilhles as in the case of the British Regional Heart Study the relatively strong corshyrelation found for calcium in England and Vales may be a result of calcium acting as a rery good surrogate for social variables The soft water areas of the north and west of the British Isles equate to tlle areas of early

100r-------------------------------------~

90 0 Suriyawewa

80 ~ Uda Walawe j( =395 mg L-1 as CaC03 (n =102)

~ Ridiyagama70i 60 u ~ 50 J

g 40 tt

30

20

10

O +-~~~~~~~-L~~~-L~~Lr~~~~

0-60 61-150 151-500 501 - 1000 gt1000

Total hardness (mg L -I as CaC03)

FIGURE 5 Histogram of total hardness values recorded for

groundwaters sampled during the wet season Uanuary and Febshyruary 200 I) from dug wells and tubewells in three subcatchments

of the Uda Walawe basin of Sri Lanka (Data courtesy of L Rajashysooriyar)

industrialization and today these areas house a disproshyportionate percentlge of the socially disadvantaged Gones amp Moon 1987) Therefore it is important thar further smdies undertake tlle challenge of quantitatively analyzing the seplrate effects of social variables fro111 those of water hardness

Fewer sUldies have been carried out in developing countries but Dissanayake et al (1982) for example found a negative correlation beveen water harclness and vlrious forms of CVD and leukemia in Sri Lanb N[ore recent sUldies (Dissanayake 1991 Rajasooriy~lr 2(03) have highlighted the problem of high fluoride concentrations and associated dental fluorosis in areas of hard water abstracted from crystalline bedrock aquifers in Sri Lanka

Rajasooriyar (2003) measured total hardness in dug vells and tubewelJs in the Uda vValawe basin of southern Sri Lanka in the wide range of7-3579mgL-1 as CaCO with an average of 395 mgL- as CaCO (Figure 5) Compared with the government water quality limit of 600 11lgL- as CaCO 12 ofthe 102 samples collected during tlle wet season in 2001 were in excesS of the limit and are considered too hard to drink (values above 100- 150mg-L-1 as CaCO j are 10cltllIy considered too hard as a water supply) Soft waters are found in are)s with a dense irrigation netvork supplied by rain-fed surface reservoirs Irrigation canal waters in the Suriyavewa and Ucla vValawe subcatchments were measshyured in the dry season to have a total hardness in the range 40-90mgL-1 as CaCO) (Rajasooriyar 2(03) and it is leakage of this water source that leads to tlle softenshy

337tVATpoundll HARDNESS AJD HEALT il EffECTS

ing ofshlllow grmmdwater The majority of the groundshywaters (63 ) in the fractured aqujfer represent very hard -lter with carb()l1ate hardness in the range 151- 500 mg L- ~s CaCO) contributed by the weathering of ferroshymagnesian minenJls anorthite calcite and dolomite T he products of this weathering lead to high concentrashytions of dissolved calcium magnesilllll and bicarbonate in gronndwaters E xceptionally high values of hardness gt 1O()OmgL - I as CaC03) typiCltl11y occur in non-irrishy

l tecl areas with additional non-carbonate hrrdness COllshy

rr ibuted by pyrite oxidation and in the case of the coastal Ri diyagam coastal catchment by salt water inputs

IV S TUDIES AT AN INDIVIDUAL LEVEL

In recent years some studies have been made with a igher precision as regards exposure classification than he previously cited ecological studies Most of them 3-e been conducted with a case-control design This

1I1S thlt the exposure to water magnesium and l icium has been estimated for i11dividuals who have uttered from the disease as well as for healthy control

-cr ons and the difference in risk calculated A simil lr Pc of study design is the prospective cohort study here the subjects are followed over time

Studies in Finland

lTI ltar and Karvonen 111lde a cohort study in 1979 I-te ~ compared the denh rate from CHI) in two rural

alt in vestern and eastern Finland The cohort -nprised men 40-59 years old in J 959 and they were ilOlred for 15 years The water data were not truly Ji-idual but were median volues in ten suhareas in the

[ern 1rea md 33 SUblleaS in the eastern area The ges of sUbltllmiddotel medians were 69- 27R I11g L - I of ter magnesium in the western area and O6- 73mgL-1

~he eastern area The cohort in eastern Finland had _ath rate hmiddotom CHD which was 1 7 times higher than

- estern cohort C alcium was not investigated few years Later Luoma et a (J983) published a

_ -control study conducted in the southeastern region - Fi nland Cases were men 30-04 year~ of age with

rt 1cute myocardial infarction (AMT alive or tlS t d) who were pair-matched with hospital conshy

fo r age and region (rmal vs urban) L1 addition ub tion controls vcre selected and matched for age m unjcipality All subjects submitted a sample of

their drinking water The range of magnesium in the drinking water was 10- 575 mgL- for the cases and 075-300mgL- and l0-160mgL- for the hospital controls and population controls respectively For caseshypopulation control comparisons the relative risk (RR) with 95deg) confidence limjts was 47 (9510 confidence interval [ell J3-253) for magnesiull1levels lower than l2 mgL - 1

bull This means that those with the lowest magshynesium levels had a risk of AiVil almost fi ve times higher than those with higher magnesium lerels For the caseshyhospital control comparisons the RR was 20 (95 CI 07- 65) that is double the risk They also found inverse relations vith fluoride levels but no relation to calcium

B Studies in Sweden

In Sweden three case-control studies have heen conshyducted during the last decade First using mortality registers the rebtion between death from AMI and the level of magnesium and calcium in drinking water was examined among men A few years later a study with a similar design WlS made comprising women The studies were conducted in southern Sweden in a relashytively small geographic area where there was a great difference between as well as within the municipalities regarding magnesium and calcium content in drinking w~lter The advantage with this lirnited study area was that the possible risk of such confounding factors as climate geographical cultural and socjoeconomic difshyferences was minimized

Seventeen municipalities were identified whose water quality vith respect to water hardness acidity and treatment procedures had been basically unchanged (change of hardness lt10 and pH lt5 ) during the most recent ten years Figure 6 shows the location of tbe 17 mUL1icipalities that comprised the study area

Cases vere men (n = 854) and women (n = 378) in 17 municipalities in southern Sweden who had died of AiVIJ between ages 50 and 69 years Controls were men (n =989) and women (n = 1368) of the same age group who had died of cancer LJdividnal water data were colshylected l~lhle II shows the number of vaterworks the range of magnesium in drinking water and the amount of magnesium in water supplied to the most densely populated area in each municipality

The subjects -were divided into quartiles according to

the levels of magnesium Odds ratios were calcula ted in relation to the group with the lowest exposure Adjustshyments for age were ll1ade in aU analyses The results show odds ratios of 065 for men and 070 for women in the quartile with highest magnesium levels in the

N

I

bull

F IGURE 6 The country of Sweden with SIlaquoine and Blekinge counties enlarged The 17 municipalities ill the studies are numbered corresponding to Table II ie I Vellinge 2 Svedala 3 Skurup 4 Hbbr 5 Ystad 6 Trelleborg 76 Gbinge 8 6rkelljunga 9 Bromblla 10 Perstorp I I Klippan 12 Astorp 13 Kristianstad 14 Sirnrishamn 15 Angelholm 16 Karlskrona and 17 Karlshamn

drinking water (298-99mgL-) (Figure 7) This meansT AB LE II Number of Waterworks Range of that the ri sk of dying from M I was about 30 lowerMagnesium (Mg) Concentrations in Drinking Water compared with the risk for those who used drinking(mgL- ) and Amount of Mg in Water Supplied to the water with the lowest levels of magnesium (RubenowitzMost Densely Populated Areas (mgL-) et al 1996 1999)

A few years later a prospective interview study was Water Mg in the conducted in the same area where men and women who

Number of Range of most densely suffered from AM I from 1994 to 19 were compared Municipality waterworks water Mg populated area with population controls (Rllbenowitz et al 20(0) The no in the study (mgL-I) (mgL I) results showed that magnesium in drinking water proshy

tected against death from AM I but the total incidence 2 59-100 100 was not affected In particular the number of deaths

2 2 68-200 200 outside hospitals was lower in the quartile with high 3 4 26-100 90 fllelgnesiurn levels This supports the hypothesis that 4 2 88-130 88

magnesium prevents sudden death from ANI rather5 5 5 1-119 75

than all CHD deaths The mechanisms that could6 4 65-180 160 explain these findings are discllssed below 7 9 33-135 50

8 3 30-69 69

9 5 13-76 13 10 2 40-90 90 II 2 55-90 80 V PHYSIOLOGICAL IM PORTA N CE 12 100 100

OF MAGNESIUM13 15 13-144 67 14 9 38-134 97

15 2 70-110 110 A Physiological Properties of 16 9 20-130 20

Magnesium in Humans17 2 19-50 20

Municipality numbers correspond to Figure 6 11agnesium is involved in several important enzymatic reactions All reactions that involve ATP (adenosine triphosphate) thelt is energy demanding reactions have an absolute magnesium requirement (Reinhardt 1988)

339 VATER HARDNESS AND H EALTH EFFECTS

OR men5 ----------------------------------------------------

0 100 1088 TI to651070

I_I )

0 --------c----------------=--=------------J s35 36-68 69-97 ~98

mg2- (mg L- )

OR women 5r ------------------~----------------------------~

108 100 0

093

r 1 r

70

5

0 s34 s35-67 68-9 8 ~99 mg2+ (mg L- )

F IGURE 7 Odds ratios (OR) with 95 confidence intervals Jr death from AMI in relation to magnesium in drinking water ~dj usted for age and calcium) in men and women

il nportant processes in the body mediated by magneshyi UJ1l are for example synthesis of protein nucleic acid nL fat glucose use neuromuscular transmission musshy

-u lar contraction and transport over cell membranes ]tura amp Altura 1996) (see also Chapter 30 this o lulle)

lagnesium is essential to the cardiovascular system nd two properties are especially important stabilizing

ilie cardiac electric system (preventing cardiac arrhythshymia) and regulating vascular tone (Reinhardt 1991) T here are multiple mechanisms behind these properties

lagnesium is needed to maintain the normal gradishy~nr of potassium and calcium over cell membranes ltura et aI 1981) It is well known that magnesium is

necessary to maintain intracellular levels of potassium T his is done by blocking the outward passage of potasshy-i Ulll through the cell membrane and by activating the ecnzvme NaK-ATPase It has a similar function in CashylTPase Magnesium also has a direct effect on potasshyiUIll and calcium channels in the cell membranes Reinhardt 1991)

Furthermore as regards impact on vascular tone Ilugnesium is a necessary activator for the synthesis of

cyclic adenosine monophosphate (c-Ai1P) which is a vasodilator It also acts as a natural calcium antagonist by competing for calcium binding sites in the vascular smooth muscle and thus reducing the constrictive effect of calcium in the blood vessels (Reinhardt 1991) In addition the vasoconstrictive actions of hormones such as angiotensin serotonin and acetylcholine are enhanced in the case of magnesium deficiency (Alhua et al 1981)

VI M AGNESIUM INTAKE

A Magnesium Deficiency

Marginal magnesium deficiency probably affects a large proportion of the population whose dietary intake does not reach the recommended amount Although severe magnesium deficiency is not common in the population hypomagnesemia is often present among hospitalized patients (Altura 1994) A survey showed that hyposhylIlagnesemia was the most common electrolyte abnorshymality in patients entering the intensive care unit and was present in 20 of the patients (Reinhardt 1988) (see also Chapter 8 this volume)

The causes of hypomagnesemia include reduced intake caused by starvation or intravenous therapy without magnesium supplement impaired absorption owing to chronic diarrhea or malabsorption syndromes increased renal loss caused by diseases such as diabetes or renal diseases or by the use of alcohol or such drugs as diuretics or antibiotics (Reinhardt 1988)

B Magnesium Intake From Food

The largest part of the total magnesium intake is from foodstuffs Magnesium is present in many foodshlffs and in large amounts in nuts beans green leafy vegshyetables and whole grain cereals Mainly because of increased industrial treatment which decreases magneshysium levels by 80 to 95 (Marier 1986h) it has been suggested that the majority of people today have a lower magnesium intake than the recommended dietary amount (RDA) of 6 mg kg-I day-I (Marier 1986b Seelig 1986 Durlach 1989) Table III shows the magnesium content in some foodstuffs and beverages

Approximately 40 of magnesium ingested in food is normally absorbed (Hardwick et aL 1990) The proshyportion absorbed is inversely related to the amount ingested however and has been shown to range between approximately 10 and 70 (Fine et aL 1991)

340 VTER HARD-IESS A--D J-IMTII EFFECTS

TABLE II Magnesium (Mg) Content in Food and Beverages

Food items and Mg (mg Food items and Mg(mg beverages loog I) beverages fOOg- l

)

Food items Food items Bread white 23 Bananas 33 Bread fiber-rich 50 Fish 25 Muesli 100 Shrimp 42 Corn flakes 16 Meat 25 Cheese 34 Eggs 13 Common beans 184 Almonds 280

white dried Common beans 131 Peanuts 188

brown dried Corn 23 Dark chocolate 130 Spinach 79 Milk chocolate 60 Avocado 39 Broccoli 23 Beverages Tomato 10 Milk 12 Cucumber 10 Coffee 5 Mushrooms 13 Tea 3 Brown rice 110 Beer low alcohol 8

content White rice 34 Beer high alcohol II

content Potatoes 24 Red wine 12 Apples 5 White wine 3 Oranges 10 Spirits 0

Magnesium content in the water not included

The absorption rate also depends on the intake of other foodstuffs Elements such as calcium phosphorus fibers and phytic acids are known to diminish the absorption rate of magnesium (Seelig 1986) Most magnesium is absorbed in the distal small intestine mainly by passive diffusion through the panlCellubr pathway but also to a smaller extent by solvent drag and active transport (Hardwick et aI 1990)

VI I WAT E R MAGNESI U M AND

BODY MAGNES I U M STATUS

A Magnesium Intake From WatershyImportance for Body Magnesium Status

Vlagnesium has a natural source in water from the weathering of a range of rock types In igneous rock

magnesium is typically a constituent of the dark colored ferromagnesian minerals which include olivine pyroxshyenes ltlm phiboles and dark colored micas In altered rocks magnesian mineral species also occllr such 1S chlorite montmorillonite and serpentine Sedimentary forms of magnesium include magnesite (MgCO) and dolomite (CaiVIg(CO)) iVlagnesiulll is substantially less 1bunclant than calcium in all rock types and 0 in most natural waters the magnesium concentration is much lower usuall y by 5-10 times than the calciuIll concentration Concentrations of I11ltlgnesium in fresh waters are controlled by solution and precipitation reactions involving magnesiurn-bearing siJjcate and carbonate minerals with concentrations typically less than 50mgL-1

although values above IOOmgL I are recorded

Magnesium intake via water depends on the level in drinking water An important issue in discussions about the relation between vater magnesium and AMI is whether magnesium in drinking water can be critical for the body magnesiulll status as the main part of the magnes ium intake derives from food (Neutra 1999) It has been suggested th n the quantitative contribution of water magnesium may be crucial for body magnesium status for those who have a low dietary intake and use water with high magnesium levels (Durlach et aI 1989) L1 addition cooking food in magnesium-poor water leaches out magnesium while cooking in magnesiul1lshyrich water diminishes this loss (Haring amp 7a n Delft 1981)

Furthermore it has been suggested that magnesium in water appearing as hydrated ions has a higher bioavaila bility than magnesium in food which i bound ill different compounds that are less easily absorbed (Durbch et al 19H9 Theophanides et aI 1990) However simultaneous intake of other agents could diminish the absorption rate as discussed above

Plants cultivated in areas with magnesium-rich water may have higher magnesium content especially if the soil is magnesium-rich and the land is irrigated with magnesium-rich water People living in such areas who eat locally grown vegetables and fruits may also benefit from an addition to the total m1gnesium intake espeshycially during slimmer months H owever genetic factors appear to have a greater effect on plant magnesium composition than do soil and environmental factors (Vilkinson et aL 1987)

Some previous studies have shown relations between water magnesium and body magnesium content In a study of baboons tap water was more effective than dietary supplementation in increasing serum levels of magnesium and zinc (Robbins amp Sly 1981 ) Anderson

341 VATER HARDgtESS AKD HEALTH EFFE CTS

et 1 1 (1975) found relations between water magnesium md magnesium content in the hea rt muscle The m~ocardial ma gnesium was approximately 7 lower J l1ong residents of citi es with soft water T here lS however no difference in magnesium content in th e diaphragm or the pectoralis major muscle Other tudies have shown relations between water magnesium lecls and the magnesium content in skeletal ll1uscie and in coromllY lrteri es (Landin et aI 1989)

In a loading test 10 subjects who normally used water u ith a magnesium level of 16 mg L-I instead ve re given drinking wa ter with 20 I11g L - I magnesium Afte r six weeks of supplementation with l1lltlgnesium-enriched I lter the excretjon of magnesium wa s increased which indicated improved body magnesium status Ruhenmvitz et aI 1998)

nother study demonstrated that the ionized se rum magnesium level was rltlised after only six days of an increased di etltlry load of magnes ium but not the total hody magnesium However a correlation between ionized serum md ioni zed intracellular magnesium was 5hown (Altura amp Al tura 1996)

From the available data it is apparent that the quanshyriteltive contribution from water may be crll cial The m agnesiumlevcls in drinking water in the Swed ish caseshyontrol studies ranged from 0 to 44mgL- I Nith a tota l h ily intake of drinking water of two liters the proporshyjomll magnesium contribution from water thus ranges

from 0 to 88mgday- l This is a percentage contribution between 0 and 25 o f the RDA of 350mgday- l For those who hlVe 1 daily intake lower thaJ1 the RDA and m e magnesium-rich water the contribution would he (~ n more important

In the prospective study the calculated in take of lagnesium from food rell1ged from 15 7 to 658mgday-l

m edian 35 6mg day- I This means that a large number of the subjects had a lower intake than the RDA One gtubject with an intake of 157 mg magnesium per day used drinking water with 35mg L-l which mea ns a 15 addition to the magnesium intake from fo od If he instead had used water with 40 mg L - I the addishy

ti nn would have been 50 and the total daily intake ~-+o mg day- I

III C ALCIUM IN D RI N KI N G W ATER

N D CARDIOVASCULAR D ISEASE

T he majority of the previolls ecological studies showed 1n inverse rela tion hetween calcium in drinking water

and CVD 15 reported above The physio logical mechshy1l1isms thlt cou ld explain the reLltionship He not clear T here is hmveer evidence that calcium defici ency can cause hypertensi on vhich is a well-known risk factor for bo th stroke and A III (La u amp E by 1985 Vloore 1989 Vltl e lgter amp Brunner 1994)

A Calcium Deficiency

Calcium deficiency is common among the elde rl y espeshyci l lJy women The absorption nnd renal conscrvltl tion of calciu m decreases vith age The absorption of calcium from food varies between 15 and 75 (Schaafsma 1992) but in menolgtlt1l1sal wom en the absorption is only about 20- 30)) (Hemy amp Recker 1985) Furthermore cllciull1 intake is often decreased among the elderly (Harlan et aI 1984) The RDA for calcium in Sweden is 800 mg day- I for adult women and 600 mg day- I fo r men In the 1nited States the RDA is 1000-1 500 111g delyi for ad ults

stud ~ comprising 61000 women in Sweden e1 ged 40-76 showed that calcium intake decreased with age and thlt1t a majo rity of postmel1opausll women had a deficie nt calcium intake (1ichae lsson 1996) Several stud ies conducted in the United States have also shown an intake lower than recommended especially amo ng women (F leming amp Heimbach 1994) For individuals with a deficiency the additional cllciul1l fro lll water could be crucial to prevent this Along with the contrishybution of drin king water cooking food in Cltllcium-rich water has been shown not only to prevent lelching hut even to increlse ca lcium levels in rhe food (Ilaring amp van Delft 1981 )

B Calcium and Blood Pressure

Several studies have shown an inverse rebtion beteen dietary calciu111 in take and blood pressure fer3shyanalysis compri si ng l1early 40000 people ha s shown that a high calcium intake lowered both systo lic and diastolic hlood pressure (Cappucio et aI 1(95) Low serum concentrltl tions of ioni 7ed Gllcium have been me1sured in patien ts with hypertension ( IcCarron 1982) There are several possible 111 echlI1i sIllS that could expLlin how ca lcium lowers bl ood pressure

One mcchelllism 111lt1 y be that hypocalcemia inhihi ts C3-ATPlse activity which 1Clt1ds to an increase in fre e intracellular calci um and colltraction of vascubr smooth muscles (McCarron 198 5) Calcium supplementatio n has been shown to be efficaci ous especially among sa ltshy

337tVATpoundll HARDNESS AJD HEALT il EffECTS

ing ofshlllow grmmdwater The majority of the groundshywaters (63 ) in the fractured aqujfer represent very hard -lter with carb()l1ate hardness in the range 151- 500 mg L- ~s CaCO) contributed by the weathering of ferroshymagnesian minenJls anorthite calcite and dolomite T he products of this weathering lead to high concentrashytions of dissolved calcium magnesilllll and bicarbonate in gronndwaters E xceptionally high values of hardness gt 1O()OmgL - I as CaC03) typiCltl11y occur in non-irrishy

l tecl areas with additional non-carbonate hrrdness COllshy

rr ibuted by pyrite oxidation and in the case of the coastal Ri diyagam coastal catchment by salt water inputs

IV S TUDIES AT AN INDIVIDUAL LEVEL

In recent years some studies have been made with a igher precision as regards exposure classification than he previously cited ecological studies Most of them 3-e been conducted with a case-control design This

1I1S thlt the exposure to water magnesium and l icium has been estimated for i11dividuals who have uttered from the disease as well as for healthy control

-cr ons and the difference in risk calculated A simil lr Pc of study design is the prospective cohort study here the subjects are followed over time

Studies in Finland

lTI ltar and Karvonen 111lde a cohort study in 1979 I-te ~ compared the denh rate from CHI) in two rural

alt in vestern and eastern Finland The cohort -nprised men 40-59 years old in J 959 and they were ilOlred for 15 years The water data were not truly Ji-idual but were median volues in ten suhareas in the

[ern 1rea md 33 SUblleaS in the eastern area The ges of sUbltllmiddotel medians were 69- 27R I11g L - I of ter magnesium in the western area and O6- 73mgL-1

~he eastern area The cohort in eastern Finland had _ath rate hmiddotom CHD which was 1 7 times higher than

- estern cohort C alcium was not investigated few years Later Luoma et a (J983) published a

_ -control study conducted in the southeastern region - Fi nland Cases were men 30-04 year~ of age with

rt 1cute myocardial infarction (AMT alive or tlS t d) who were pair-matched with hospital conshy

fo r age and region (rmal vs urban) L1 addition ub tion controls vcre selected and matched for age m unjcipality All subjects submitted a sample of

their drinking water The range of magnesium in the drinking water was 10- 575 mgL- for the cases and 075-300mgL- and l0-160mgL- for the hospital controls and population controls respectively For caseshypopulation control comparisons the relative risk (RR) with 95deg) confidence limjts was 47 (9510 confidence interval [ell J3-253) for magnesiull1levels lower than l2 mgL - 1

bull This means that those with the lowest magshynesium levels had a risk of AiVil almost fi ve times higher than those with higher magnesium lerels For the caseshyhospital control comparisons the RR was 20 (95 CI 07- 65) that is double the risk They also found inverse relations vith fluoride levels but no relation to calcium

B Studies in Sweden

In Sweden three case-control studies have heen conshyducted during the last decade First using mortality registers the rebtion between death from AMI and the level of magnesium and calcium in drinking water was examined among men A few years later a study with a similar design WlS made comprising women The studies were conducted in southern Sweden in a relashytively small geographic area where there was a great difference between as well as within the municipalities regarding magnesium and calcium content in drinking w~lter The advantage with this lirnited study area was that the possible risk of such confounding factors as climate geographical cultural and socjoeconomic difshyferences was minimized

Seventeen municipalities were identified whose water quality vith respect to water hardness acidity and treatment procedures had been basically unchanged (change of hardness lt10 and pH lt5 ) during the most recent ten years Figure 6 shows the location of tbe 17 mUL1icipalities that comprised the study area

Cases vere men (n = 854) and women (n = 378) in 17 municipalities in southern Sweden who had died of AiVIJ between ages 50 and 69 years Controls were men (n =989) and women (n = 1368) of the same age group who had died of cancer LJdividnal water data were colshylected l~lhle II shows the number of vaterworks the range of magnesium in drinking water and the amount of magnesium in water supplied to the most densely populated area in each municipality

The subjects -were divided into quartiles according to

the levels of magnesium Odds ratios were calcula ted in relation to the group with the lowest exposure Adjustshyments for age were ll1ade in aU analyses The results show odds ratios of 065 for men and 070 for women in the quartile with highest magnesium levels in the

N

I

bull

F IGURE 6 The country of Sweden with SIlaquoine and Blekinge counties enlarged The 17 municipalities ill the studies are numbered corresponding to Table II ie I Vellinge 2 Svedala 3 Skurup 4 Hbbr 5 Ystad 6 Trelleborg 76 Gbinge 8 6rkelljunga 9 Bromblla 10 Perstorp I I Klippan 12 Astorp 13 Kristianstad 14 Sirnrishamn 15 Angelholm 16 Karlskrona and 17 Karlshamn

drinking water (298-99mgL-) (Figure 7) This meansT AB LE II Number of Waterworks Range of that the ri sk of dying from M I was about 30 lowerMagnesium (Mg) Concentrations in Drinking Water compared with the risk for those who used drinking(mgL- ) and Amount of Mg in Water Supplied to the water with the lowest levels of magnesium (RubenowitzMost Densely Populated Areas (mgL-) et al 1996 1999)

A few years later a prospective interview study was Water Mg in the conducted in the same area where men and women who

Number of Range of most densely suffered from AM I from 1994 to 19 were compared Municipality waterworks water Mg populated area with population controls (Rllbenowitz et al 20(0) The no in the study (mgL-I) (mgL I) results showed that magnesium in drinking water proshy

tected against death from AM I but the total incidence 2 59-100 100 was not affected In particular the number of deaths

2 2 68-200 200 outside hospitals was lower in the quartile with high 3 4 26-100 90 fllelgnesiurn levels This supports the hypothesis that 4 2 88-130 88

magnesium prevents sudden death from ANI rather5 5 5 1-119 75

than all CHD deaths The mechanisms that could6 4 65-180 160 explain these findings are discllssed below 7 9 33-135 50

8 3 30-69 69

9 5 13-76 13 10 2 40-90 90 II 2 55-90 80 V PHYSIOLOGICAL IM PORTA N CE 12 100 100

OF MAGNESIUM13 15 13-144 67 14 9 38-134 97

15 2 70-110 110 A Physiological Properties of 16 9 20-130 20

Magnesium in Humans17 2 19-50 20

Municipality numbers correspond to Figure 6 11agnesium is involved in several important enzymatic reactions All reactions that involve ATP (adenosine triphosphate) thelt is energy demanding reactions have an absolute magnesium requirement (Reinhardt 1988)

339 VATER HARDNESS AND H EALTH EFFECTS

OR men5 ----------------------------------------------------

0 100 1088 TI to651070

I_I )

0 --------c----------------=--=------------J s35 36-68 69-97 ~98

mg2- (mg L- )

OR women 5r ------------------~----------------------------~

108 100 0

093

r 1 r

70

5

0 s34 s35-67 68-9 8 ~99 mg2+ (mg L- )

F IGURE 7 Odds ratios (OR) with 95 confidence intervals Jr death from AMI in relation to magnesium in drinking water ~dj usted for age and calcium) in men and women

il nportant processes in the body mediated by magneshyi UJ1l are for example synthesis of protein nucleic acid nL fat glucose use neuromuscular transmission musshy

-u lar contraction and transport over cell membranes ]tura amp Altura 1996) (see also Chapter 30 this o lulle)

lagnesium is essential to the cardiovascular system nd two properties are especially important stabilizing

ilie cardiac electric system (preventing cardiac arrhythshymia) and regulating vascular tone (Reinhardt 1991) T here are multiple mechanisms behind these properties

lagnesium is needed to maintain the normal gradishy~nr of potassium and calcium over cell membranes ltura et aI 1981) It is well known that magnesium is

necessary to maintain intracellular levels of potassium T his is done by blocking the outward passage of potasshy-i Ulll through the cell membrane and by activating the ecnzvme NaK-ATPase It has a similar function in CashylTPase Magnesium also has a direct effect on potasshyiUIll and calcium channels in the cell membranes Reinhardt 1991)

Furthermore as regards impact on vascular tone Ilugnesium is a necessary activator for the synthesis of

cyclic adenosine monophosphate (c-Ai1P) which is a vasodilator It also acts as a natural calcium antagonist by competing for calcium binding sites in the vascular smooth muscle and thus reducing the constrictive effect of calcium in the blood vessels (Reinhardt 1991) In addition the vasoconstrictive actions of hormones such as angiotensin serotonin and acetylcholine are enhanced in the case of magnesium deficiency (Alhua et al 1981)

VI M AGNESIUM INTAKE

A Magnesium Deficiency

Marginal magnesium deficiency probably affects a large proportion of the population whose dietary intake does not reach the recommended amount Although severe magnesium deficiency is not common in the population hypomagnesemia is often present among hospitalized patients (Altura 1994) A survey showed that hyposhylIlagnesemia was the most common electrolyte abnorshymality in patients entering the intensive care unit and was present in 20 of the patients (Reinhardt 1988) (see also Chapter 8 this volume)

The causes of hypomagnesemia include reduced intake caused by starvation or intravenous therapy without magnesium supplement impaired absorption owing to chronic diarrhea or malabsorption syndromes increased renal loss caused by diseases such as diabetes or renal diseases or by the use of alcohol or such drugs as diuretics or antibiotics (Reinhardt 1988)

B Magnesium Intake From Food

The largest part of the total magnesium intake is from foodstuffs Magnesium is present in many foodshlffs and in large amounts in nuts beans green leafy vegshyetables and whole grain cereals Mainly because of increased industrial treatment which decreases magneshysium levels by 80 to 95 (Marier 1986h) it has been suggested that the majority of people today have a lower magnesium intake than the recommended dietary amount (RDA) of 6 mg kg-I day-I (Marier 1986b Seelig 1986 Durlach 1989) Table III shows the magnesium content in some foodstuffs and beverages

Approximately 40 of magnesium ingested in food is normally absorbed (Hardwick et aL 1990) The proshyportion absorbed is inversely related to the amount ingested however and has been shown to range between approximately 10 and 70 (Fine et aL 1991)

340 VTER HARD-IESS A--D J-IMTII EFFECTS

TABLE II Magnesium (Mg) Content in Food and Beverages

Food items and Mg (mg Food items and Mg(mg beverages loog I) beverages fOOg- l

)

Food items Food items Bread white 23 Bananas 33 Bread fiber-rich 50 Fish 25 Muesli 100 Shrimp 42 Corn flakes 16 Meat 25 Cheese 34 Eggs 13 Common beans 184 Almonds 280

white dried Common beans 131 Peanuts 188

brown dried Corn 23 Dark chocolate 130 Spinach 79 Milk chocolate 60 Avocado 39 Broccoli 23 Beverages Tomato 10 Milk 12 Cucumber 10 Coffee 5 Mushrooms 13 Tea 3 Brown rice 110 Beer low alcohol 8

content White rice 34 Beer high alcohol II

content Potatoes 24 Red wine 12 Apples 5 White wine 3 Oranges 10 Spirits 0

Magnesium content in the water not included

The absorption rate also depends on the intake of other foodstuffs Elements such as calcium phosphorus fibers and phytic acids are known to diminish the absorption rate of magnesium (Seelig 1986) Most magnesium is absorbed in the distal small intestine mainly by passive diffusion through the panlCellubr pathway but also to a smaller extent by solvent drag and active transport (Hardwick et aI 1990)

VI I WAT E R MAGNESI U M AND

BODY MAGNES I U M STATUS

A Magnesium Intake From WatershyImportance for Body Magnesium Status

Vlagnesium has a natural source in water from the weathering of a range of rock types In igneous rock

magnesium is typically a constituent of the dark colored ferromagnesian minerals which include olivine pyroxshyenes ltlm phiboles and dark colored micas In altered rocks magnesian mineral species also occllr such 1S chlorite montmorillonite and serpentine Sedimentary forms of magnesium include magnesite (MgCO) and dolomite (CaiVIg(CO)) iVlagnesiulll is substantially less 1bunclant than calcium in all rock types and 0 in most natural waters the magnesium concentration is much lower usuall y by 5-10 times than the calciuIll concentration Concentrations of I11ltlgnesium in fresh waters are controlled by solution and precipitation reactions involving magnesiurn-bearing siJjcate and carbonate minerals with concentrations typically less than 50mgL-1

although values above IOOmgL I are recorded

Magnesium intake via water depends on the level in drinking water An important issue in discussions about the relation between vater magnesium and AMI is whether magnesium in drinking water can be critical for the body magnesiulll status as the main part of the magnes ium intake derives from food (Neutra 1999) It has been suggested th n the quantitative contribution of water magnesium may be crucial for body magnesium status for those who have a low dietary intake and use water with high magnesium levels (Durlach et aI 1989) L1 addition cooking food in magnesium-poor water leaches out magnesium while cooking in magnesiul1lshyrich water diminishes this loss (Haring amp 7a n Delft 1981)

Furthermore it has been suggested that magnesium in water appearing as hydrated ions has a higher bioavaila bility than magnesium in food which i bound ill different compounds that are less easily absorbed (Durbch et al 19H9 Theophanides et aI 1990) However simultaneous intake of other agents could diminish the absorption rate as discussed above

Plants cultivated in areas with magnesium-rich water may have higher magnesium content especially if the soil is magnesium-rich and the land is irrigated with magnesium-rich water People living in such areas who eat locally grown vegetables and fruits may also benefit from an addition to the total m1gnesium intake espeshycially during slimmer months H owever genetic factors appear to have a greater effect on plant magnesium composition than do soil and environmental factors (Vilkinson et aL 1987)

Some previous studies have shown relations between water magnesium and body magnesium content In a study of baboons tap water was more effective than dietary supplementation in increasing serum levels of magnesium and zinc (Robbins amp Sly 1981 ) Anderson

341 VATER HARDgtESS AKD HEALTH EFFE CTS

et 1 1 (1975) found relations between water magnesium md magnesium content in the hea rt muscle The m~ocardial ma gnesium was approximately 7 lower J l1ong residents of citi es with soft water T here lS however no difference in magnesium content in th e diaphragm or the pectoralis major muscle Other tudies have shown relations between water magnesium lecls and the magnesium content in skeletal ll1uscie and in coromllY lrteri es (Landin et aI 1989)

In a loading test 10 subjects who normally used water u ith a magnesium level of 16 mg L-I instead ve re given drinking wa ter with 20 I11g L - I magnesium Afte r six weeks of supplementation with l1lltlgnesium-enriched I lter the excretjon of magnesium wa s increased which indicated improved body magnesium status Ruhenmvitz et aI 1998)

nother study demonstrated that the ionized se rum magnesium level was rltlised after only six days of an increased di etltlry load of magnes ium but not the total hody magnesium However a correlation between ionized serum md ioni zed intracellular magnesium was 5hown (Altura amp Al tura 1996)

From the available data it is apparent that the quanshyriteltive contribution from water may be crll cial The m agnesiumlevcls in drinking water in the Swed ish caseshyontrol studies ranged from 0 to 44mgL- I Nith a tota l h ily intake of drinking water of two liters the proporshyjomll magnesium contribution from water thus ranges

from 0 to 88mgday- l This is a percentage contribution between 0 and 25 o f the RDA of 350mgday- l For those who hlVe 1 daily intake lower thaJ1 the RDA and m e magnesium-rich water the contribution would he (~ n more important

In the prospective study the calculated in take of lagnesium from food rell1ged from 15 7 to 658mgday-l

m edian 35 6mg day- I This means that a large number of the subjects had a lower intake than the RDA One gtubject with an intake of 157 mg magnesium per day used drinking water with 35mg L-l which mea ns a 15 addition to the magnesium intake from fo od If he instead had used water with 40 mg L - I the addishy

ti nn would have been 50 and the total daily intake ~-+o mg day- I

III C ALCIUM IN D RI N KI N G W ATER

N D CARDIOVASCULAR D ISEASE

T he majority of the previolls ecological studies showed 1n inverse rela tion hetween calcium in drinking water

and CVD 15 reported above The physio logical mechshy1l1isms thlt cou ld explain the reLltionship He not clear T here is hmveer evidence that calcium defici ency can cause hypertensi on vhich is a well-known risk factor for bo th stroke and A III (La u amp E by 1985 Vloore 1989 Vltl e lgter amp Brunner 1994)

A Calcium Deficiency

Calcium deficiency is common among the elde rl y espeshyci l lJy women The absorption nnd renal conscrvltl tion of calciu m decreases vith age The absorption of calcium from food varies between 15 and 75 (Schaafsma 1992) but in menolgtlt1l1sal wom en the absorption is only about 20- 30)) (Hemy amp Recker 1985) Furthermore cllciull1 intake is often decreased among the elderly (Harlan et aI 1984) The RDA for calcium in Sweden is 800 mg day- I for adult women and 600 mg day- I fo r men In the 1nited States the RDA is 1000-1 500 111g delyi for ad ults

stud ~ comprising 61000 women in Sweden e1 ged 40-76 showed that calcium intake decreased with age and thlt1t a majo rity of postmel1opausll women had a deficie nt calcium intake (1ichae lsson 1996) Several stud ies conducted in the United States have also shown an intake lower than recommended especially amo ng women (F leming amp Heimbach 1994) For individuals with a deficiency the additional cllciul1l fro lll water could be crucial to prevent this Along with the contrishybution of drin king water cooking food in Cltllcium-rich water has been shown not only to prevent lelching hut even to increlse ca lcium levels in rhe food (Ilaring amp van Delft 1981 )

B Calcium and Blood Pressure

Several studies have shown an inverse rebtion beteen dietary calciu111 in take and blood pressure fer3shyanalysis compri si ng l1early 40000 people ha s shown that a high calcium intake lowered both systo lic and diastolic hlood pressure (Cappucio et aI 1(95) Low serum concentrltl tions of ioni 7ed Gllcium have been me1sured in patien ts with hypertension ( IcCarron 1982) There are several possible 111 echlI1i sIllS that could expLlin how ca lcium lowers bl ood pressure

One mcchelllism 111lt1 y be that hypocalcemia inhihi ts C3-ATPlse activity which 1Clt1ds to an increase in fre e intracellular calci um and colltraction of vascubr smooth muscles (McCarron 198 5) Calcium supplementatio n has been shown to be efficaci ous especially among sa ltshy

N

I

bull

F IGURE 6 The country of Sweden with SIlaquoine and Blekinge counties enlarged The 17 municipalities ill the studies are numbered corresponding to Table II ie I Vellinge 2 Svedala 3 Skurup 4 Hbbr 5 Ystad 6 Trelleborg 76 Gbinge 8 6rkelljunga 9 Bromblla 10 Perstorp I I Klippan 12 Astorp 13 Kristianstad 14 Sirnrishamn 15 Angelholm 16 Karlskrona and 17 Karlshamn

drinking water (298-99mgL-) (Figure 7) This meansT AB LE II Number of Waterworks Range of that the ri sk of dying from M I was about 30 lowerMagnesium (Mg) Concentrations in Drinking Water compared with the risk for those who used drinking(mgL- ) and Amount of Mg in Water Supplied to the water with the lowest levels of magnesium (RubenowitzMost Densely Populated Areas (mgL-) et al 1996 1999)

A few years later a prospective interview study was Water Mg in the conducted in the same area where men and women who

Number of Range of most densely suffered from AM I from 1994 to 19 were compared Municipality waterworks water Mg populated area with population controls (Rllbenowitz et al 20(0) The no in the study (mgL-I) (mgL I) results showed that magnesium in drinking water proshy

tected against death from AM I but the total incidence 2 59-100 100 was not affected In particular the number of deaths

2 2 68-200 200 outside hospitals was lower in the quartile with high 3 4 26-100 90 fllelgnesiurn levels This supports the hypothesis that 4 2 88-130 88

magnesium prevents sudden death from ANI rather5 5 5 1-119 75

than all CHD deaths The mechanisms that could6 4 65-180 160 explain these findings are discllssed below 7 9 33-135 50

8 3 30-69 69

9 5 13-76 13 10 2 40-90 90 II 2 55-90 80 V PHYSIOLOGICAL IM PORTA N CE 12 100 100

OF MAGNESIUM13 15 13-144 67 14 9 38-134 97

15 2 70-110 110 A Physiological Properties of 16 9 20-130 20

Magnesium in Humans17 2 19-50 20

Municipality numbers correspond to Figure 6 11agnesium is involved in several important enzymatic reactions All reactions that involve ATP (adenosine triphosphate) thelt is energy demanding reactions have an absolute magnesium requirement (Reinhardt 1988)

339 VATER HARDNESS AND H EALTH EFFECTS

OR men5 ----------------------------------------------------

0 100 1088 TI to651070

I_I )

0 --------c----------------=--=------------J s35 36-68 69-97 ~98

mg2- (mg L- )

OR women 5r ------------------~----------------------------~

108 100 0

093

r 1 r

70

5

0 s34 s35-67 68-9 8 ~99 mg2+ (mg L- )

F IGURE 7 Odds ratios (OR) with 95 confidence intervals Jr death from AMI in relation to magnesium in drinking water ~dj usted for age and calcium) in men and women

il nportant processes in the body mediated by magneshyi UJ1l are for example synthesis of protein nucleic acid nL fat glucose use neuromuscular transmission musshy

-u lar contraction and transport over cell membranes ]tura amp Altura 1996) (see also Chapter 30 this o lulle)

lagnesium is essential to the cardiovascular system nd two properties are especially important stabilizing

ilie cardiac electric system (preventing cardiac arrhythshymia) and regulating vascular tone (Reinhardt 1991) T here are multiple mechanisms behind these properties

lagnesium is needed to maintain the normal gradishy~nr of potassium and calcium over cell membranes ltura et aI 1981) It is well known that magnesium is

necessary to maintain intracellular levels of potassium T his is done by blocking the outward passage of potasshy-i Ulll through the cell membrane and by activating the ecnzvme NaK-ATPase It has a similar function in CashylTPase Magnesium also has a direct effect on potasshyiUIll and calcium channels in the cell membranes Reinhardt 1991)

Furthermore as regards impact on vascular tone Ilugnesium is a necessary activator for the synthesis of

cyclic adenosine monophosphate (c-Ai1P) which is a vasodilator It also acts as a natural calcium antagonist by competing for calcium binding sites in the vascular smooth muscle and thus reducing the constrictive effect of calcium in the blood vessels (Reinhardt 1991) In addition the vasoconstrictive actions of hormones such as angiotensin serotonin and acetylcholine are enhanced in the case of magnesium deficiency (Alhua et al 1981)

VI M AGNESIUM INTAKE

A Magnesium Deficiency

Marginal magnesium deficiency probably affects a large proportion of the population whose dietary intake does not reach the recommended amount Although severe magnesium deficiency is not common in the population hypomagnesemia is often present among hospitalized patients (Altura 1994) A survey showed that hyposhylIlagnesemia was the most common electrolyte abnorshymality in patients entering the intensive care unit and was present in 20 of the patients (Reinhardt 1988) (see also Chapter 8 this volume)

The causes of hypomagnesemia include reduced intake caused by starvation or intravenous therapy without magnesium supplement impaired absorption owing to chronic diarrhea or malabsorption syndromes increased renal loss caused by diseases such as diabetes or renal diseases or by the use of alcohol or such drugs as diuretics or antibiotics (Reinhardt 1988)

B Magnesium Intake From Food

The largest part of the total magnesium intake is from foodstuffs Magnesium is present in many foodshlffs and in large amounts in nuts beans green leafy vegshyetables and whole grain cereals Mainly because of increased industrial treatment which decreases magneshysium levels by 80 to 95 (Marier 1986h) it has been suggested that the majority of people today have a lower magnesium intake than the recommended dietary amount (RDA) of 6 mg kg-I day-I (Marier 1986b Seelig 1986 Durlach 1989) Table III shows the magnesium content in some foodstuffs and beverages

Approximately 40 of magnesium ingested in food is normally absorbed (Hardwick et aL 1990) The proshyportion absorbed is inversely related to the amount ingested however and has been shown to range between approximately 10 and 70 (Fine et aL 1991)

340 VTER HARD-IESS A--D J-IMTII EFFECTS

TABLE II Magnesium (Mg) Content in Food and Beverages

Food items and Mg (mg Food items and Mg(mg beverages loog I) beverages fOOg- l

)

Food items Food items Bread white 23 Bananas 33 Bread fiber-rich 50 Fish 25 Muesli 100 Shrimp 42 Corn flakes 16 Meat 25 Cheese 34 Eggs 13 Common beans 184 Almonds 280

white dried Common beans 131 Peanuts 188

brown dried Corn 23 Dark chocolate 130 Spinach 79 Milk chocolate 60 Avocado 39 Broccoli 23 Beverages Tomato 10 Milk 12 Cucumber 10 Coffee 5 Mushrooms 13 Tea 3 Brown rice 110 Beer low alcohol 8

content White rice 34 Beer high alcohol II

content Potatoes 24 Red wine 12 Apples 5 White wine 3 Oranges 10 Spirits 0

Magnesium content in the water not included

The absorption rate also depends on the intake of other foodstuffs Elements such as calcium phosphorus fibers and phytic acids are known to diminish the absorption rate of magnesium (Seelig 1986) Most magnesium is absorbed in the distal small intestine mainly by passive diffusion through the panlCellubr pathway but also to a smaller extent by solvent drag and active transport (Hardwick et aI 1990)

VI I WAT E R MAGNESI U M AND

BODY MAGNES I U M STATUS

A Magnesium Intake From WatershyImportance for Body Magnesium Status

Vlagnesium has a natural source in water from the weathering of a range of rock types In igneous rock

magnesium is typically a constituent of the dark colored ferromagnesian minerals which include olivine pyroxshyenes ltlm phiboles and dark colored micas In altered rocks magnesian mineral species also occllr such 1S chlorite montmorillonite and serpentine Sedimentary forms of magnesium include magnesite (MgCO) and dolomite (CaiVIg(CO)) iVlagnesiulll is substantially less 1bunclant than calcium in all rock types and 0 in most natural waters the magnesium concentration is much lower usuall y by 5-10 times than the calciuIll concentration Concentrations of I11ltlgnesium in fresh waters are controlled by solution and precipitation reactions involving magnesiurn-bearing siJjcate and carbonate minerals with concentrations typically less than 50mgL-1

although values above IOOmgL I are recorded

Magnesium intake via water depends on the level in drinking water An important issue in discussions about the relation between vater magnesium and AMI is whether magnesium in drinking water can be critical for the body magnesiulll status as the main part of the magnes ium intake derives from food (Neutra 1999) It has been suggested th n the quantitative contribution of water magnesium may be crucial for body magnesium status for those who have a low dietary intake and use water with high magnesium levels (Durlach et aI 1989) L1 addition cooking food in magnesium-poor water leaches out magnesium while cooking in magnesiul1lshyrich water diminishes this loss (Haring amp 7a n Delft 1981)

Furthermore it has been suggested that magnesium in water appearing as hydrated ions has a higher bioavaila bility than magnesium in food which i bound ill different compounds that are less easily absorbed (Durbch et al 19H9 Theophanides et aI 1990) However simultaneous intake of other agents could diminish the absorption rate as discussed above

Plants cultivated in areas with magnesium-rich water may have higher magnesium content especially if the soil is magnesium-rich and the land is irrigated with magnesium-rich water People living in such areas who eat locally grown vegetables and fruits may also benefit from an addition to the total m1gnesium intake espeshycially during slimmer months H owever genetic factors appear to have a greater effect on plant magnesium composition than do soil and environmental factors (Vilkinson et aL 1987)

Some previous studies have shown relations between water magnesium and body magnesium content In a study of baboons tap water was more effective than dietary supplementation in increasing serum levels of magnesium and zinc (Robbins amp Sly 1981 ) Anderson

341 VATER HARDgtESS AKD HEALTH EFFE CTS

et 1 1 (1975) found relations between water magnesium md magnesium content in the hea rt muscle The m~ocardial ma gnesium was approximately 7 lower J l1ong residents of citi es with soft water T here lS however no difference in magnesium content in th e diaphragm or the pectoralis major muscle Other tudies have shown relations between water magnesium lecls and the magnesium content in skeletal ll1uscie and in coromllY lrteri es (Landin et aI 1989)

In a loading test 10 subjects who normally used water u ith a magnesium level of 16 mg L-I instead ve re given drinking wa ter with 20 I11g L - I magnesium Afte r six weeks of supplementation with l1lltlgnesium-enriched I lter the excretjon of magnesium wa s increased which indicated improved body magnesium status Ruhenmvitz et aI 1998)

nother study demonstrated that the ionized se rum magnesium level was rltlised after only six days of an increased di etltlry load of magnes ium but not the total hody magnesium However a correlation between ionized serum md ioni zed intracellular magnesium was 5hown (Altura amp Al tura 1996)

From the available data it is apparent that the quanshyriteltive contribution from water may be crll cial The m agnesiumlevcls in drinking water in the Swed ish caseshyontrol studies ranged from 0 to 44mgL- I Nith a tota l h ily intake of drinking water of two liters the proporshyjomll magnesium contribution from water thus ranges

from 0 to 88mgday- l This is a percentage contribution between 0 and 25 o f the RDA of 350mgday- l For those who hlVe 1 daily intake lower thaJ1 the RDA and m e magnesium-rich water the contribution would he (~ n more important

In the prospective study the calculated in take of lagnesium from food rell1ged from 15 7 to 658mgday-l

m edian 35 6mg day- I This means that a large number of the subjects had a lower intake than the RDA One gtubject with an intake of 157 mg magnesium per day used drinking water with 35mg L-l which mea ns a 15 addition to the magnesium intake from fo od If he instead had used water with 40 mg L - I the addishy

ti nn would have been 50 and the total daily intake ~-+o mg day- I

III C ALCIUM IN D RI N KI N G W ATER

N D CARDIOVASCULAR D ISEASE

T he majority of the previolls ecological studies showed 1n inverse rela tion hetween calcium in drinking water

and CVD 15 reported above The physio logical mechshy1l1isms thlt cou ld explain the reLltionship He not clear T here is hmveer evidence that calcium defici ency can cause hypertensi on vhich is a well-known risk factor for bo th stroke and A III (La u amp E by 1985 Vloore 1989 Vltl e lgter amp Brunner 1994)

A Calcium Deficiency

Calcium deficiency is common among the elde rl y espeshyci l lJy women The absorption nnd renal conscrvltl tion of calciu m decreases vith age The absorption of calcium from food varies between 15 and 75 (Schaafsma 1992) but in menolgtlt1l1sal wom en the absorption is only about 20- 30)) (Hemy amp Recker 1985) Furthermore cllciull1 intake is often decreased among the elderly (Harlan et aI 1984) The RDA for calcium in Sweden is 800 mg day- I for adult women and 600 mg day- I fo r men In the 1nited States the RDA is 1000-1 500 111g delyi for ad ults

stud ~ comprising 61000 women in Sweden e1 ged 40-76 showed that calcium intake decreased with age and thlt1t a majo rity of postmel1opausll women had a deficie nt calcium intake (1ichae lsson 1996) Several stud ies conducted in the United States have also shown an intake lower than recommended especially amo ng women (F leming amp Heimbach 1994) For individuals with a deficiency the additional cllciul1l fro lll water could be crucial to prevent this Along with the contrishybution of drin king water cooking food in Cltllcium-rich water has been shown not only to prevent lelching hut even to increlse ca lcium levels in rhe food (Ilaring amp van Delft 1981 )

B Calcium and Blood Pressure

Several studies have shown an inverse rebtion beteen dietary calciu111 in take and blood pressure fer3shyanalysis compri si ng l1early 40000 people ha s shown that a high calcium intake lowered both systo lic and diastolic hlood pressure (Cappucio et aI 1(95) Low serum concentrltl tions of ioni 7ed Gllcium have been me1sured in patien ts with hypertension ( IcCarron 1982) There are several possible 111 echlI1i sIllS that could expLlin how ca lcium lowers bl ood pressure

One mcchelllism 111lt1 y be that hypocalcemia inhihi ts C3-ATPlse activity which 1Clt1ds to an increase in fre e intracellular calci um and colltraction of vascubr smooth muscles (McCarron 198 5) Calcium supplementatio n has been shown to be efficaci ous especially among sa ltshy

339 VATER HARDNESS AND H EALTH EFFECTS

OR men5 ----------------------------------------------------

0 100 1088 TI to651070

I_I )

0 --------c----------------=--=------------J s35 36-68 69-97 ~98

mg2- (mg L- )

OR women 5r ------------------~----------------------------~

108 100 0

093

r 1 r

70

5

0 s34 s35-67 68-9 8 ~99 mg2+ (mg L- )

F IGURE 7 Odds ratios (OR) with 95 confidence intervals Jr death from AMI in relation to magnesium in drinking water ~dj usted for age and calcium) in men and women

il nportant processes in the body mediated by magneshyi UJ1l are for example synthesis of protein nucleic acid nL fat glucose use neuromuscular transmission musshy

-u lar contraction and transport over cell membranes ]tura amp Altura 1996) (see also Chapter 30 this o lulle)

lagnesium is essential to the cardiovascular system nd two properties are especially important stabilizing

ilie cardiac electric system (preventing cardiac arrhythshymia) and regulating vascular tone (Reinhardt 1991) T here are multiple mechanisms behind these properties

lagnesium is needed to maintain the normal gradishy~nr of potassium and calcium over cell membranes ltura et aI 1981) It is well known that magnesium is

necessary to maintain intracellular levels of potassium T his is done by blocking the outward passage of potasshy-i Ulll through the cell membrane and by activating the ecnzvme NaK-ATPase It has a similar function in CashylTPase Magnesium also has a direct effect on potasshyiUIll and calcium channels in the cell membranes Reinhardt 1991)

Furthermore as regards impact on vascular tone Ilugnesium is a necessary activator for the synthesis of

cyclic adenosine monophosphate (c-Ai1P) which is a vasodilator It also acts as a natural calcium antagonist by competing for calcium binding sites in the vascular smooth muscle and thus reducing the constrictive effect of calcium in the blood vessels (Reinhardt 1991) In addition the vasoconstrictive actions of hormones such as angiotensin serotonin and acetylcholine are enhanced in the case of magnesium deficiency (Alhua et al 1981)

VI M AGNESIUM INTAKE

A Magnesium Deficiency

Marginal magnesium deficiency probably affects a large proportion of the population whose dietary intake does not reach the recommended amount Although severe magnesium deficiency is not common in the population hypomagnesemia is often present among hospitalized patients (Altura 1994) A survey showed that hyposhylIlagnesemia was the most common electrolyte abnorshymality in patients entering the intensive care unit and was present in 20 of the patients (Reinhardt 1988) (see also Chapter 8 this volume)

The causes of hypomagnesemia include reduced intake caused by starvation or intravenous therapy without magnesium supplement impaired absorption owing to chronic diarrhea or malabsorption syndromes increased renal loss caused by diseases such as diabetes or renal diseases or by the use of alcohol or such drugs as diuretics or antibiotics (Reinhardt 1988)

B Magnesium Intake From Food

The largest part of the total magnesium intake is from foodstuffs Magnesium is present in many foodshlffs and in large amounts in nuts beans green leafy vegshyetables and whole grain cereals Mainly because of increased industrial treatment which decreases magneshysium levels by 80 to 95 (Marier 1986h) it has been suggested that the majority of people today have a lower magnesium intake than the recommended dietary amount (RDA) of 6 mg kg-I day-I (Marier 1986b Seelig 1986 Durlach 1989) Table III shows the magnesium content in some foodstuffs and beverages

Approximately 40 of magnesium ingested in food is normally absorbed (Hardwick et aL 1990) The proshyportion absorbed is inversely related to the amount ingested however and has been shown to range between approximately 10 and 70 (Fine et aL 1991)

340 VTER HARD-IESS A--D J-IMTII EFFECTS

TABLE II Magnesium (Mg) Content in Food and Beverages

Food items and Mg (mg Food items and Mg(mg beverages loog I) beverages fOOg- l

)

Food items Food items Bread white 23 Bananas 33 Bread fiber-rich 50 Fish 25 Muesli 100 Shrimp 42 Corn flakes 16 Meat 25 Cheese 34 Eggs 13 Common beans 184 Almonds 280

white dried Common beans 131 Peanuts 188

brown dried Corn 23 Dark chocolate 130 Spinach 79 Milk chocolate 60 Avocado 39 Broccoli 23 Beverages Tomato 10 Milk 12 Cucumber 10 Coffee 5 Mushrooms 13 Tea 3 Brown rice 110 Beer low alcohol 8

content White rice 34 Beer high alcohol II

content Potatoes 24 Red wine 12 Apples 5 White wine 3 Oranges 10 Spirits 0

Magnesium content in the water not included

The absorption rate also depends on the intake of other foodstuffs Elements such as calcium phosphorus fibers and phytic acids are known to diminish the absorption rate of magnesium (Seelig 1986) Most magnesium is absorbed in the distal small intestine mainly by passive diffusion through the panlCellubr pathway but also to a smaller extent by solvent drag and active transport (Hardwick et aI 1990)

VI I WAT E R MAGNESI U M AND

BODY MAGNES I U M STATUS

A Magnesium Intake From WatershyImportance for Body Magnesium Status

Vlagnesium has a natural source in water from the weathering of a range of rock types In igneous rock

magnesium is typically a constituent of the dark colored ferromagnesian minerals which include olivine pyroxshyenes ltlm phiboles and dark colored micas In altered rocks magnesian mineral species also occllr such 1S chlorite montmorillonite and serpentine Sedimentary forms of magnesium include magnesite (MgCO) and dolomite (CaiVIg(CO)) iVlagnesiulll is substantially less 1bunclant than calcium in all rock types and 0 in most natural waters the magnesium concentration is much lower usuall y by 5-10 times than the calciuIll concentration Concentrations of I11ltlgnesium in fresh waters are controlled by solution and precipitation reactions involving magnesiurn-bearing siJjcate and carbonate minerals with concentrations typically less than 50mgL-1

although values above IOOmgL I are recorded

Magnesium intake via water depends on the level in drinking water An important issue in discussions about the relation between vater magnesium and AMI is whether magnesium in drinking water can be critical for the body magnesiulll status as the main part of the magnes ium intake derives from food (Neutra 1999) It has been suggested th n the quantitative contribution of water magnesium may be crucial for body magnesium status for those who have a low dietary intake and use water with high magnesium levels (Durlach et aI 1989) L1 addition cooking food in magnesium-poor water leaches out magnesium while cooking in magnesiul1lshyrich water diminishes this loss (Haring amp 7a n Delft 1981)

Furthermore it has been suggested that magnesium in water appearing as hydrated ions has a higher bioavaila bility than magnesium in food which i bound ill different compounds that are less easily absorbed (Durbch et al 19H9 Theophanides et aI 1990) However simultaneous intake of other agents could diminish the absorption rate as discussed above

Plants cultivated in areas with magnesium-rich water may have higher magnesium content especially if the soil is magnesium-rich and the land is irrigated with magnesium-rich water People living in such areas who eat locally grown vegetables and fruits may also benefit from an addition to the total m1gnesium intake espeshycially during slimmer months H owever genetic factors appear to have a greater effect on plant magnesium composition than do soil and environmental factors (Vilkinson et aL 1987)

Some previous studies have shown relations between water magnesium and body magnesium content In a study of baboons tap water was more effective than dietary supplementation in increasing serum levels of magnesium and zinc (Robbins amp Sly 1981 ) Anderson

341 VATER HARDgtESS AKD HEALTH EFFE CTS

et 1 1 (1975) found relations between water magnesium md magnesium content in the hea rt muscle The m~ocardial ma gnesium was approximately 7 lower J l1ong residents of citi es with soft water T here lS however no difference in magnesium content in th e diaphragm or the pectoralis major muscle Other tudies have shown relations between water magnesium lecls and the magnesium content in skeletal ll1uscie and in coromllY lrteri es (Landin et aI 1989)

In a loading test 10 subjects who normally used water u ith a magnesium level of 16 mg L-I instead ve re given drinking wa ter with 20 I11g L - I magnesium Afte r six weeks of supplementation with l1lltlgnesium-enriched I lter the excretjon of magnesium wa s increased which indicated improved body magnesium status Ruhenmvitz et aI 1998)

nother study demonstrated that the ionized se rum magnesium level was rltlised after only six days of an increased di etltlry load of magnes ium but not the total hody magnesium However a correlation between ionized serum md ioni zed intracellular magnesium was 5hown (Altura amp Al tura 1996)

From the available data it is apparent that the quanshyriteltive contribution from water may be crll cial The m agnesiumlevcls in drinking water in the Swed ish caseshyontrol studies ranged from 0 to 44mgL- I Nith a tota l h ily intake of drinking water of two liters the proporshyjomll magnesium contribution from water thus ranges

from 0 to 88mgday- l This is a percentage contribution between 0 and 25 o f the RDA of 350mgday- l For those who hlVe 1 daily intake lower thaJ1 the RDA and m e magnesium-rich water the contribution would he (~ n more important

In the prospective study the calculated in take of lagnesium from food rell1ged from 15 7 to 658mgday-l

m edian 35 6mg day- I This means that a large number of the subjects had a lower intake than the RDA One gtubject with an intake of 157 mg magnesium per day used drinking water with 35mg L-l which mea ns a 15 addition to the magnesium intake from fo od If he instead had used water with 40 mg L - I the addishy

ti nn would have been 50 and the total daily intake ~-+o mg day- I

III C ALCIUM IN D RI N KI N G W ATER

N D CARDIOVASCULAR D ISEASE

T he majority of the previolls ecological studies showed 1n inverse rela tion hetween calcium in drinking water

and CVD 15 reported above The physio logical mechshy1l1isms thlt cou ld explain the reLltionship He not clear T here is hmveer evidence that calcium defici ency can cause hypertensi on vhich is a well-known risk factor for bo th stroke and A III (La u amp E by 1985 Vloore 1989 Vltl e lgter amp Brunner 1994)

A Calcium Deficiency

Calcium deficiency is common among the elde rl y espeshyci l lJy women The absorption nnd renal conscrvltl tion of calciu m decreases vith age The absorption of calcium from food varies between 15 and 75 (Schaafsma 1992) but in menolgtlt1l1sal wom en the absorption is only about 20- 30)) (Hemy amp Recker 1985) Furthermore cllciull1 intake is often decreased among the elderly (Harlan et aI 1984) The RDA for calcium in Sweden is 800 mg day- I for adult women and 600 mg day- I fo r men In the 1nited States the RDA is 1000-1 500 111g delyi for ad ults

stud ~ comprising 61000 women in Sweden e1 ged 40-76 showed that calcium intake decreased with age and thlt1t a majo rity of postmel1opausll women had a deficie nt calcium intake (1ichae lsson 1996) Several stud ies conducted in the United States have also shown an intake lower than recommended especially amo ng women (F leming amp Heimbach 1994) For individuals with a deficiency the additional cllciul1l fro lll water could be crucial to prevent this Along with the contrishybution of drin king water cooking food in Cltllcium-rich water has been shown not only to prevent lelching hut even to increlse ca lcium levels in rhe food (Ilaring amp van Delft 1981 )

B Calcium and Blood Pressure

Several studies have shown an inverse rebtion beteen dietary calciu111 in take and blood pressure fer3shyanalysis compri si ng l1early 40000 people ha s shown that a high calcium intake lowered both systo lic and diastolic hlood pressure (Cappucio et aI 1(95) Low serum concentrltl tions of ioni 7ed Gllcium have been me1sured in patien ts with hypertension ( IcCarron 1982) There are several possible 111 echlI1i sIllS that could expLlin how ca lcium lowers bl ood pressure

One mcchelllism 111lt1 y be that hypocalcemia inhihi ts C3-ATPlse activity which 1Clt1ds to an increase in fre e intracellular calci um and colltraction of vascubr smooth muscles (McCarron 198 5) Calcium supplementatio n has been shown to be efficaci ous especially among sa ltshy

340 VTER HARD-IESS A--D J-IMTII EFFECTS

TABLE II Magnesium (Mg) Content in Food and Beverages

Food items and Mg (mg Food items and Mg(mg beverages loog I) beverages fOOg- l

)

Food items Food items Bread white 23 Bananas 33 Bread fiber-rich 50 Fish 25 Muesli 100 Shrimp 42 Corn flakes 16 Meat 25 Cheese 34 Eggs 13 Common beans 184 Almonds 280

white dried Common beans 131 Peanuts 188

brown dried Corn 23 Dark chocolate 130 Spinach 79 Milk chocolate 60 Avocado 39 Broccoli 23 Beverages Tomato 10 Milk 12 Cucumber 10 Coffee 5 Mushrooms 13 Tea 3 Brown rice 110 Beer low alcohol 8

content White rice 34 Beer high alcohol II

content Potatoes 24 Red wine 12 Apples 5 White wine 3 Oranges 10 Spirits 0

Magnesium content in the water not included

The absorption rate also depends on the intake of other foodstuffs Elements such as calcium phosphorus fibers and phytic acids are known to diminish the absorption rate of magnesium (Seelig 1986) Most magnesium is absorbed in the distal small intestine mainly by passive diffusion through the panlCellubr pathway but also to a smaller extent by solvent drag and active transport (Hardwick et aI 1990)

VI I WAT E R MAGNESI U M AND

BODY MAGNES I U M STATUS

A Magnesium Intake From WatershyImportance for Body Magnesium Status

Vlagnesium has a natural source in water from the weathering of a range of rock types In igneous rock

magnesium is typically a constituent of the dark colored ferromagnesian minerals which include olivine pyroxshyenes ltlm phiboles and dark colored micas In altered rocks magnesian mineral species also occllr such 1S chlorite montmorillonite and serpentine Sedimentary forms of magnesium include magnesite (MgCO) and dolomite (CaiVIg(CO)) iVlagnesiulll is substantially less 1bunclant than calcium in all rock types and 0 in most natural waters the magnesium concentration is much lower usuall y by 5-10 times than the calciuIll concentration Concentrations of I11ltlgnesium in fresh waters are controlled by solution and precipitation reactions involving magnesiurn-bearing siJjcate and carbonate minerals with concentrations typically less than 50mgL-1

although values above IOOmgL I are recorded

Magnesium intake via water depends on the level in drinking water An important issue in discussions about the relation between vater magnesium and AMI is whether magnesium in drinking water can be critical for the body magnesiulll status as the main part of the magnes ium intake derives from food (Neutra 1999) It has been suggested th n the quantitative contribution of water magnesium may be crucial for body magnesium status for those who have a low dietary intake and use water with high magnesium levels (Durlach et aI 1989) L1 addition cooking food in magnesium-poor water leaches out magnesium while cooking in magnesiul1lshyrich water diminishes this loss (Haring amp 7a n Delft 1981)

Furthermore it has been suggested that magnesium in water appearing as hydrated ions has a higher bioavaila bility than magnesium in food which i bound ill different compounds that are less easily absorbed (Durbch et al 19H9 Theophanides et aI 1990) However simultaneous intake of other agents could diminish the absorption rate as discussed above

Plants cultivated in areas with magnesium-rich water may have higher magnesium content especially if the soil is magnesium-rich and the land is irrigated with magnesium-rich water People living in such areas who eat locally grown vegetables and fruits may also benefit from an addition to the total m1gnesium intake espeshycially during slimmer months H owever genetic factors appear to have a greater effect on plant magnesium composition than do soil and environmental factors (Vilkinson et aL 1987)

Some previous studies have shown relations between water magnesium and body magnesium content In a study of baboons tap water was more effective than dietary supplementation in increasing serum levels of magnesium and zinc (Robbins amp Sly 1981 ) Anderson

341 VATER HARDgtESS AKD HEALTH EFFE CTS

et 1 1 (1975) found relations between water magnesium md magnesium content in the hea rt muscle The m~ocardial ma gnesium was approximately 7 lower J l1ong residents of citi es with soft water T here lS however no difference in magnesium content in th e diaphragm or the pectoralis major muscle Other tudies have shown relations between water magnesium lecls and the magnesium content in skeletal ll1uscie and in coromllY lrteri es (Landin et aI 1989)

In a loading test 10 subjects who normally used water u ith a magnesium level of 16 mg L-I instead ve re given drinking wa ter with 20 I11g L - I magnesium Afte r six weeks of supplementation with l1lltlgnesium-enriched I lter the excretjon of magnesium wa s increased which indicated improved body magnesium status Ruhenmvitz et aI 1998)

nother study demonstrated that the ionized se rum magnesium level was rltlised after only six days of an increased di etltlry load of magnes ium but not the total hody magnesium However a correlation between ionized serum md ioni zed intracellular magnesium was 5hown (Altura amp Al tura 1996)

From the available data it is apparent that the quanshyriteltive contribution from water may be crll cial The m agnesiumlevcls in drinking water in the Swed ish caseshyontrol studies ranged from 0 to 44mgL- I Nith a tota l h ily intake of drinking water of two liters the proporshyjomll magnesium contribution from water thus ranges

from 0 to 88mgday- l This is a percentage contribution between 0 and 25 o f the RDA of 350mgday- l For those who hlVe 1 daily intake lower thaJ1 the RDA and m e magnesium-rich water the contribution would he (~ n more important

In the prospective study the calculated in take of lagnesium from food rell1ged from 15 7 to 658mgday-l

m edian 35 6mg day- I This means that a large number of the subjects had a lower intake than the RDA One gtubject with an intake of 157 mg magnesium per day used drinking water with 35mg L-l which mea ns a 15 addition to the magnesium intake from fo od If he instead had used water with 40 mg L - I the addishy

ti nn would have been 50 and the total daily intake ~-+o mg day- I

III C ALCIUM IN D RI N KI N G W ATER

N D CARDIOVASCULAR D ISEASE

T he majority of the previolls ecological studies showed 1n inverse rela tion hetween calcium in drinking water

and CVD 15 reported above The physio logical mechshy1l1isms thlt cou ld explain the reLltionship He not clear T here is hmveer evidence that calcium defici ency can cause hypertensi on vhich is a well-known risk factor for bo th stroke and A III (La u amp E by 1985 Vloore 1989 Vltl e lgter amp Brunner 1994)

A Calcium Deficiency

Calcium deficiency is common among the elde rl y espeshyci l lJy women The absorption nnd renal conscrvltl tion of calciu m decreases vith age The absorption of calcium from food varies between 15 and 75 (Schaafsma 1992) but in menolgtlt1l1sal wom en the absorption is only about 20- 30)) (Hemy amp Recker 1985) Furthermore cllciull1 intake is often decreased among the elderly (Harlan et aI 1984) The RDA for calcium in Sweden is 800 mg day- I for adult women and 600 mg day- I fo r men In the 1nited States the RDA is 1000-1 500 111g delyi for ad ults

stud ~ comprising 61000 women in Sweden e1 ged 40-76 showed that calcium intake decreased with age and thlt1t a majo rity of postmel1opausll women had a deficie nt calcium intake (1ichae lsson 1996) Several stud ies conducted in the United States have also shown an intake lower than recommended especially amo ng women (F leming amp Heimbach 1994) For individuals with a deficiency the additional cllciul1l fro lll water could be crucial to prevent this Along with the contrishybution of drin king water cooking food in Cltllcium-rich water has been shown not only to prevent lelching hut even to increlse ca lcium levels in rhe food (Ilaring amp van Delft 1981 )

B Calcium and Blood Pressure

Several studies have shown an inverse rebtion beteen dietary calciu111 in take and blood pressure fer3shyanalysis compri si ng l1early 40000 people ha s shown that a high calcium intake lowered both systo lic and diastolic hlood pressure (Cappucio et aI 1(95) Low serum concentrltl tions of ioni 7ed Gllcium have been me1sured in patien ts with hypertension ( IcCarron 1982) There are several possible 111 echlI1i sIllS that could expLlin how ca lcium lowers bl ood pressure

One mcchelllism 111lt1 y be that hypocalcemia inhihi ts C3-ATPlse activity which 1Clt1ds to an increase in fre e intracellular calci um and colltraction of vascubr smooth muscles (McCarron 198 5) Calcium supplementatio n has been shown to be efficaci ous especially among sa ltshy

341 VATER HARDgtESS AKD HEALTH EFFE CTS

et 1 1 (1975) found relations between water magnesium md magnesium content in the hea rt muscle The m~ocardial ma gnesium was approximately 7 lower J l1ong residents of citi es with soft water T here lS however no difference in magnesium content in th e diaphragm or the pectoralis major muscle Other tudies have shown relations between water magnesium lecls and the magnesium content in skeletal ll1uscie and in coromllY lrteri es (Landin et aI 1989)

In a loading test 10 subjects who normally used water u ith a magnesium level of 16 mg L-I instead ve re given drinking wa ter with 20 I11g L - I magnesium Afte r six weeks of supplementation with l1lltlgnesium-enriched I lter the excretjon of magnesium wa s increased which indicated improved body magnesium status Ruhenmvitz et aI 1998)

nother study demonstrated that the ionized se rum magnesium level was rltlised after only six days of an increased di etltlry load of magnes ium but not the total hody magnesium However a correlation between ionized serum md ioni zed intracellular magnesium was 5hown (Altura amp Al tura 1996)

From the available data it is apparent that the quanshyriteltive contribution from water may be crll cial The m agnesiumlevcls in drinking water in the Swed ish caseshyontrol studies ranged from 0 to 44mgL- I Nith a tota l h ily intake of drinking water of two liters the proporshyjomll magnesium contribution from water thus ranges

from 0 to 88mgday- l This is a percentage contribution between 0 and 25 o f the RDA of 350mgday- l For those who hlVe 1 daily intake lower thaJ1 the RDA and m e magnesium-rich water the contribution would he (~ n more important

In the prospective study the calculated in take of lagnesium from food rell1ged from 15 7 to 658mgday-l

m edian 35 6mg day- I This means that a large number of the subjects had a lower intake than the RDA One gtubject with an intake of 157 mg magnesium per day used drinking water with 35mg L-l which mea ns a 15 addition to the magnesium intake from fo od If he instead had used water with 40 mg L - I the addishy

ti nn would have been 50 and the total daily intake ~-+o mg day- I

III C ALCIUM IN D RI N KI N G W ATER

N D CARDIOVASCULAR D ISEASE

T he majority of the previolls ecological studies showed 1n inverse rela tion hetween calcium in drinking water

and CVD 15 reported above The physio logical mechshy1l1isms thlt cou ld explain the reLltionship He not clear T here is hmveer evidence that calcium defici ency can cause hypertensi on vhich is a well-known risk factor for bo th stroke and A III (La u amp E by 1985 Vloore 1989 Vltl e lgter amp Brunner 1994)

A Calcium Deficiency

Calcium deficiency is common among the elde rl y espeshyci l lJy women The absorption nnd renal conscrvltl tion of calciu m decreases vith age The absorption of calcium from food varies between 15 and 75 (Schaafsma 1992) but in menolgtlt1l1sal wom en the absorption is only about 20- 30)) (Hemy amp Recker 1985) Furthermore cllciull1 intake is often decreased among the elderly (Harlan et aI 1984) The RDA for calcium in Sweden is 800 mg day- I for adult women and 600 mg day- I fo r men In the 1nited States the RDA is 1000-1 500 111g delyi for ad ults

stud ~ comprising 61000 women in Sweden e1 ged 40-76 showed that calcium intake decreased with age and thlt1t a majo rity of postmel1opausll women had a deficie nt calcium intake (1ichae lsson 1996) Several stud ies conducted in the United States have also shown an intake lower than recommended especially amo ng women (F leming amp Heimbach 1994) For individuals with a deficiency the additional cllciul1l fro lll water could be crucial to prevent this Along with the contrishybution of drin king water cooking food in Cltllcium-rich water has been shown not only to prevent lelching hut even to increlse ca lcium levels in rhe food (Ilaring amp van Delft 1981 )

B Calcium and Blood Pressure

Several studies have shown an inverse rebtion beteen dietary calciu111 in take and blood pressure fer3shyanalysis compri si ng l1early 40000 people ha s shown that a high calcium intake lowered both systo lic and diastolic hlood pressure (Cappucio et aI 1(95) Low serum concentrltl tions of ioni 7ed Gllcium have been me1sured in patien ts with hypertension ( IcCarron 1982) There are several possible 111 echlI1i sIllS that could expLlin how ca lcium lowers bl ood pressure

One mcchelllism 111lt1 y be that hypocalcemia inhihi ts C3-ATPlse activity which 1Clt1ds to an increase in fre e intracellular calci um and colltraction of vascubr smooth muscles (McCarron 198 5) Calcium supplementatio n has been shown to be efficaci ous especially among sa ltshy

342 VVATER HARD~ESS A N D HE-UTH EFFECTS

cnSlove bypertensives with a deficient basal calcium intake (Sowers et al 1991) These individuals often lun increased levels of the calcium regulatory horshymones parathyroid hormone and active vitamin D O25-(OH)c-D) which can cause increased peripheral resistance Dietary calcium suppresses these hormones middothich causes the blood pressure to decrease Calcium ~l1d calcium regulatory hormones may also influence blood pressure regulation via the central nervous system Calcium also induces natriuresis which has been shown to lower blood pressure in posouenopausaL hypertensive women Gohnson et aI 1985)

The case-control studies reported above showed no clear relation between calcium and AMI

IX WATER HARDNESS AND

OTHER HEALTH EFFECTS

The results of several studies have suggested that a variety of other diseases are also correlated with water hardness which include various types of cancer Incishydences of a correlation between cancer and water hardness have been reported from studies in Finland and Tliwan In northern Finland correlations of ageshyadjusted incidences of various forms of cancer with the geochemical composition of groundwater were undershytaken by comparing geochemical maps showing the hardness uranium iron and nitrate content of water and maps showing the areal distribution of the incishydences of ten forms of cancer (Piispanen 1991) A stashytistically significant positive correlation was identified between water hardness and several forms of cancer especially for all forms of cancer combined in the female population (r = 066) Piispanen (1991) suggested that drinking hard water may be an initiator and promoter of cancer although it is admitted that a positive correshylation between the geochemical and medical variables does not necessarily prove a cause-and-effect relation-hip between these variables More recent research in

Taiwan also proposes a possible association between middotater hardness in drinking water and several types of (Ulcer In a study of esophageal cancer Yang et al 1999) set up control groups that consisted of people

who h~d died from causes other than cancer and the cont rols middotere pair-matched to the cancer cases by sex ltlr o f hirth and year of death For esophageal cancer the re ults showed that there was a 42 excess risk of morrality fiom esophageal cancer in relation to the use

In a Japanese study of water hardness regional geoshylogical features and the incidence of struvite stoncs Kohri et al (1993) found a positive correlation betwecn the magnesium-calcium ratio of tap water and the incishydence of sOuvite stones The incidence of struvite stones was both high in regions of basaJt and sedimenshytary rock and low in granite and limestone areas

In an ecological study of the relation between domesshytic water hardness and the prevalence of eczema among primary-school-age children in Nottingham England lvIer ally et a1 (I (98) found a significant direct relation between a one-year period and lifetime prevalence of eczema and water hardness both before and after adjustment for confounding factors (sex age socioecoshynomic status access to health care) Eczema prcvalence trends in the secondary-school population were not significant

X CONCLUSIONS AND CONSEQUENCES

The significance of earlier studies of the link between water hardness and CVD is unclear and it is suggested that the reported associations may reflect disease patterns that can be explained by social climatological and environmental factors rather than by the hardness of the water However from the results of epidemioshylogical and experimental studies the most significant conclusion is that magnesium in drinking water preshyvents death from AMI either by preventing arrhythmia or spasm in coronary blood vessels It is not difficult to

llnagll1e the importance of these findings for public health

A A Public Health Perspective

lvlarier and Neri (1985) attempted to quantify the importance of water magnesium using a number of the abovementioned epidemiological studies They estishymated that an increase in water magnesium level of 6 mgL-1 would decrease CHD mortality by approxishymately I oX

The data collected in the Swedish case-control studies can be used to estimate the impact of water magnesium on the incidence of myocardial inElrction in the study population If everyone in the male study base were to drink water from the highest quartile

343 VAT ER HARD-ESS A-D HLLTII EFFECTS

~1) 8mgL- I) the decrease in mortality from AMI ould be about 19 This means that the age-specific

Inc idence of death from myocardial infarction in tbe rudy lrea would change from about 3501100000 year- 1

0 285100000 year- I The decrease of the incidence rmgL- magnesium can be calculated to be approxishy

lJ tely 10100000 year- which is an even larger I~(case than Marier and Neri (1985) estimated

For women the corresponding decrease in mortality -0111 ANIT would be about 25 if everyone were to

Jrink water from the highest quartile (~99 mg L- I) The ~e-specific mortality among women in the study rel would change from about 92100000 year- I to

71 00000 year-I

B Consequences

llat should be the consequences of todays knowledge It I recoIllmended intake of magnesium Is there suffishy_i~nt evidence to recommend an increased intake of TTlagnesium If so should the recommendation be applishy_l ble to the whole population or only to certain ri sk =TOUps) Furthermore whn would be the best way to ~crease magnesium intake

The consumption of magnesium-rich food and water an be encouraged and the use of water softeners in r ClS with hard water discouraged At least one tap with n fi ltered water for drinking should always be left

-U though such reco1l11l1enclltltions are hardly con trovershyaI it is difficult to make them effective especially if

-- e target is the population as a whole TheorcticalJy a possible way of increasing magneshy

TU m intake would be to add magnesium to drinking Iter especially in areas with naturally soft water This

- already done in some waterworks in order to reduce l ITosiveness To do so on a larger scale would

- n leVer be expensive and politically difficnlt Recommendations to use oral magnesinm suppleshy

mentation would not be practically feasible for the hole population but could be considered to be

rected toward certain risk groups Before a general prevention program can be

cepted large-scale intervention studies mUSt be conshyueted to accurately evaluate the preventive effect of

)~mesium This would require several thousands of middotJhjects however and wonld thus be cumbersome and

pensive Nevertheless in view of the significant implishyations for public health such studies should be conshyucted The possibility of a simple and harmless WlY of

-middotmiddotJucing ANn mortality rate must not be overlooked

SEE ALSO THE FOLLOWING CHAPTERS

Chapter 5 (Uptake of Elements ti-om a Biological Point of View) Chapter 8 (Biological Responses of E lements) Ch8pter 22 (Environmental iVledicine) C hlpter 23 (Environmental Pathology) Chlptel 31 Llodeling Groundwater Flow and Quality)

FURTHER READING

Altura B bull1 (1994) Introduction Importance oLlagnesium

in Physiology and Medicine and the eed for Ion Selecshy

tive Electrodes SClIld J Clill Iab Imelt 54 Supplement

2175-9

AI nll-a B V1 and Altura B T (1996) Role of 11agnesium

in Paro-physiological Processes and the Clinical Utility of

Vlagnesium Ion Selective Electrodes SCfll1fi J Clill rub hnmiddotest 56 Supplement 224 211-234

Altura B M Altura B T Carella A and TurJapary P D

VI V (l9S 1) Hypomagnesemia 111d Vasoconstriction

Possible Relation to Etiology of Sudden Death Ischemic

Heart Disease and H ypertensive V)scular Disease Arwy 9 212-231

Anderson T Vo eri L c Schreiner G B Ellbot F D

F and Zdrojewski A (1975) Ischemi c Helrt Diselsc

Vater Hardness and Myocardial 1agn esiul1l Call _HLl Assoc 113 199-203

Cappucio F Elliot P All end er P S Pryer] Follman P A and Cutler ] 1 (1995) Epidemiologic Association

Between Dietary Calcium Intake anel Blood Pressure

lIeta-Analysis of Published Datl Am [jJidcllliol 142 935-945

Dawson E B Frey 1 ] Vloore T D and _1cG~l1ity J (1978) Rebtionship of Metal Metabolism to -ascu Llr

Disease 1ortality Rates in Texas Am J ClillYll fi 1

1lflR-I 1 97

Dissanayake C B (1991) The Fluoride Pronlem in the

Groundwater of Sri Lanb - Environmentll bJLlgement

and Health Int J l~llVi1on )wd 3fl l) 7-15 (

Diss3lllyake C B Senanltne A and eerasoori~a ~ R (1982) Geochemistry of Vell 1ter and Cmliol ascul ar

Diseases in Sri Lanka lilt FllcmiddotilII Stild 19 195shy

203

Durlach ] (198)) Recol11mended Dietary Al110unts of

vIagnesium iagnesiu111 RD- 1Iagllcs Res 2 195 shy

203

Dur1lt1Ch] Bara 1 and Guict-Bara A (19fj 9) 1a gnesium

Level in Drinking 1 tel Its Importance in Cardiovascushy

343 VAT ER HARD-ESS A-D HLLTII EFFECTS

~1) 8mgL- I) the decrease in mortality from AMI ould be about 19 This means that the age-specific

Inc idence of death from myocardial infarction in tbe rudy lrea would change from about 3501100000 year- 1

0 285100000 year- I The decrease of the incidence rmgL- magnesium can be calculated to be approxishy

lJ tely 10100000 year- which is an even larger I~(case than Marier and Neri (1985) estimated

For women the corresponding decrease in mortality -0111 ANIT would be about 25 if everyone were to

Jrink water from the highest quartile (~99 mg L- I) The ~e-specific mortality among women in the study rel would change from about 92100000 year- I to

71 00000 year-I

B Consequences

llat should be the consequences of todays knowledge It I recoIllmended intake of magnesium Is there suffishy_i~nt evidence to recommend an increased intake of TTlagnesium If so should the recommendation be applishy_l ble to the whole population or only to certain ri sk =TOUps) Furthermore whn would be the best way to ~crease magnesium intake

The consumption of magnesium-rich food and water an be encouraged and the use of water softeners in r ClS with hard water discouraged At least one tap with n fi ltered water for drinking should always be left

-U though such reco1l11l1enclltltions are hardly con trovershyaI it is difficult to make them effective especially if

-- e target is the population as a whole TheorcticalJy a possible way of increasing magneshy

TU m intake would be to add magnesium to drinking Iter especially in areas with naturally soft water This

- already done in some waterworks in order to reduce l ITosiveness To do so on a larger scale would

- n leVer be expensive and politically difficnlt Recommendations to use oral magnesinm suppleshy

mentation would not be practically feasible for the hole population but could be considered to be

rected toward certain risk groups Before a general prevention program can be

cepted large-scale intervention studies mUSt be conshyueted to accurately evaluate the preventive effect of

)~mesium This would require several thousands of middotJhjects however and wonld thus be cumbersome and

pensive Nevertheless in view of the significant implishyations for public health such studies should be conshyucted The possibility of a simple and harmless WlY of

-middotmiddotJucing ANn mortality rate must not be overlooked

SEE ALSO THE FOLLOWING CHAPTERS

Chapter 5 (Uptake of Elements ti-om a Biological Point of View) Chapter 8 (Biological Responses of E lements) Ch8pter 22 (Environmental iVledicine) C hlpter 23 (Environmental Pathology) Chlptel 31 Llodeling Groundwater Flow and Quality)

FURTHER READING

Altura B bull1 (1994) Introduction Importance oLlagnesium

in Physiology and Medicine and the eed for Ion Selecshy

tive Electrodes SClIld J Clill Iab Imelt 54 Supplement

2175-9

AI nll-a B V1 and Altura B T (1996) Role of 11agnesium

in Paro-physiological Processes and the Clinical Utility of

Vlagnesium Ion Selective Electrodes SCfll1fi J Clill rub hnmiddotest 56 Supplement 224 211-234

Altura B M Altura B T Carella A and TurJapary P D

VI V (l9S 1) Hypomagnesemia 111d Vasoconstriction

Possible Relation to Etiology of Sudden Death Ischemic

Heart Disease and H ypertensive V)scular Disease Arwy 9 212-231

Anderson T Vo eri L c Schreiner G B Ellbot F D

F and Zdrojewski A (1975) Ischemi c Helrt Diselsc

Vater Hardness and Myocardial 1agn esiul1l Call _HLl Assoc 113 199-203

Cappucio F Elliot P All end er P S Pryer] Follman P A and Cutler ] 1 (1995) Epidemiologic Association

Between Dietary Calcium Intake anel Blood Pressure

lIeta-Analysis of Published Datl Am [jJidcllliol 142 935-945

Dawson E B Frey 1 ] Vloore T D and _1cG~l1ity J (1978) Rebtionship of Metal Metabolism to -ascu Llr

Disease 1ortality Rates in Texas Am J ClillYll fi 1

1lflR-I 1 97

Dissanayake C B (1991) The Fluoride Pronlem in the

Groundwater of Sri Lanb - Environmentll bJLlgement

and Health Int J l~llVi1on )wd 3fl l) 7-15 (

Diss3lllyake C B Senanltne A and eerasoori~a ~ R (1982) Geochemistry of Vell 1ter and Cmliol ascul ar

Diseases in Sri Lanka lilt FllcmiddotilII Stild 19 195shy

203

Durlach ] (198)) Recol11mended Dietary Al110unts of

vIagnesium iagnesiu111 RD- 1Iagllcs Res 2 195 shy

203

Dur1lt1Ch] Bara 1 and Guict-Bara A (19fj 9) 1a gnesium

Level in Drinking 1 tel Its Importance in Cardiovascushy

344

lar Risk In VlognesilllJl ill Heriltb olld DisCflse (Y Itobw) and

] DurJach Eds) John Libbey amp Co London

Fine K D Santa Ana C A Porter J L md Fordtran J S (1991) Inres tinJ Absorptioll of Magnesiull1 from Food

and Supplements] CliJl Innst 88 396-402

F leming K H and Heimbach J T (1994) Consumption of

Calcium from the S Food Sources and Inr) ke levels J N UI7 J24 1426S-1430S

freeze R A and Chcrry J (1l)7l) CIOll11hv(ter Prentice

IIall Englewood Cliffs New Jersey

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I-bring B S A and van Delft V (I981) ChlI1ges in the

Mineral Composition of food as a Result of Cooking

in Hard and Soft welters ATeb Enviroll Hmltb ~6 33shy

35 Harlan vY R Hull A L Sehl11ouder R L Landis J R

Thompson f E and Larkin F A (1984) Blood Pressure

and Nutrition in Adults 1111] Epidemiol 120 17-2R

I-l ea ny R P and Recker R R (1985) Estimation of True

Calcil1m Absorption A7I1I ItbullVled 103 516-521

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C hl racteristics of lHllral Va ter (3rd edition) United

States Geological Survey vVater Supply Paper 2254

Hiscock K and Paci A (2000) Groundwater Resources in

the Quaternary Deposits and Lower Paleozoic Bedrock

of the Rheidol C~tchl11ent Vest Vales In Crou7hater ill tbe Celtic Regiolls Studies ill Hord Roc flwl QII(MIlfll )

I-1ydrogrolopy j T S Rohins and B D R Misstear Eds)

Geological Society London Special Publications 182

141 - 155

Johnson N E Smith I L and Freudenhil11] L (19tl5)

Effects on Blood Pressure of Calciul11 Supplementation of

Vomen 1111 J Clin 1110 42 12-17

Jones K and Moon G (1987) flmltb Diseflle (md Society

1 Criti((I Medi((fl Geogropby Routledge amp Kegan Paul

London 134-140

Kobayashi J (1957) On eographical Relations Between the

Chemical Nature o f Ri ve r Vatcr and Death Rate frOI1l

Apoplexv Jerich Obrt1ll lllst LlilldlJil1scb Bioi 11 12-21

Kohri K Ishikawa Y Iguchi 1 Kurita T O kada Y and

Y()shidl O (1993) Relationship Between the Incidence of

Infection Stones and the Magnesium-Calcium Ratio ofIiJp

rate r Ul middotolog Res 21 269-272

LlI1din K Bonevik II Rylander R and Sandstriim B

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MagnesiulTl Level MrtgJl(jmiddot Bull 11 177- 179

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Hypertension Hyperte71lmiddotioll 7657-667

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van der Byl K ( 1983) MagnesiuIll and Deaths Ascribed to

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LUOI11) H Aromaa A Helminen S tVIurtom)a H Kivilushy

oto L Punsar S and Knekt P (1983) Risk of Myocarshy

dial Infarction in Finnish Men in Relation to Fluoride

NbgnesiuIl1 and Cllciul11 Concentrltion in Drinking

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JVbrier J R (1986b) i[agnesitun Content of the Food Supply

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H)p cIIClIJiolJ 7 607-627

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