Drinking water salinity (sodium) and blood pressure

Water-related crises are not a new problem in Bangladesh. About 53% of the coastal area is affected by

different degrees of salinity (Islam 2004). The coastal area in Bangladesh constitutes 20% of the

country; the population living in this area relies heavily on rivers, ponds and groundwater, for washing,

bathing, and obtaining drinking water. Ponds in these areas are primarily rain fed, but the water often

mixes with saline water from rivers, soil runoff, and shallow groundwater (Rahman and Ravenscroft

2003). Approximately 20 million people who live along the coast are affected by varying degrees of

salinity in drinking water obtained from various natural sources [Ministry of Environment and Forest

(MOEF) 2006]. This salinity is moving further inland, and over time the population at risk is on the

increase. As the salinity increases it can be expected that the likelihood health consequences would

increase if such water is used for drinking and cooking.

The salt, NaCl accounts for almost 85.7% of the dissolved salts that causes salinity of water. The other

major components of seawater are magnesium (Mg), calcium (Ca), potassium (K) and sulfate (SO 4).

Therefore any effects of salinity of drinking water on blood pressure could be result of ingested sodium

through drinking water. A technical report produced by WHO and the FAO recommended ingestion of

less than 5 g sodium chloride (or 2 g sodium) per day as a population intake permissible limit, while

ensuring that the salt is iodized (WHO, 2003). This expert consultation stressed that dietary intake of

sodium from all sources influences blood pressure levels in the population and should be limited so as to

reduce the risk of coronary heart disease and stroke. A strong evidence of the link between excessive salt

consumption and several chronic diseases (WHO, 2006) has been established. 

Observational studies and clinical trials performed in general populations provide overwhelming

evidence that higher salt intake is associated with raised blood pressure (Alderman 2000; He and

MacGregor 2007; Law et al. 1991; Midgley et al. 1996). Intersalt study demonstrated an association

between salt intake and elevated blood pressure (Intersalt Cooperative Research Group 1988) and

reported that sodium intake > 1.8 g/day was associated with a 3-mmHg increase in systolic blood pres-

sure and 0.1 mmHg increase in diastolic blood pressure (Elliott et al. 1996).

The relationship between elevated sodium intake and hypertension has been the subject of considerable

scientific controversy. Although short-term studies have suggested that such a relationship does exist

(Luft FC et al. 1979), most people in western Europe and North America ingest a high salt diet from

infancy yet do not exhibit persistent hypertension until the fourth decade (WHO 1979).

Whereas reducing the sodium intake can reduce the blood pressure of some individuals with

hypertension, this is not effective in all cases (Laragh JH, Pecker MS. 1983). In case of children, several

studies suggest that high levels of sodium in drinking-water are associated with increased blood pressure

in children (Tuthill RW, Calabrese EJ. 1981; ), in other studies no such association has been found

(Pomrehn PR et al. 1983; Armstrong BK et al. 1982).

The sodium ion is ubiquitous in water and is naturally present in all foods and may be added during food

processing. Food is the main source of daily exposure to sodium, primarily as sodium chloride.

In Western Europe and North America, the estimated overall consumption of dietary sodium chloride is

5–20 g/day (2–8 g of sodium per day), the average being 10 g/day (4 g of sodium) (WHO 1979). People

on a low sodium diet need to restrict their sodium intake to less than 2 g/day (National Academy of

Sciences 1977).

The consumption of drinking-water containing 20 mg of sodium per litre would lead to a daily intake of

about 40 mg of sodium. Results from a recent study in Bangladesh (Khan et al, 2011) has revealed that

average per capita estimated sodium intakes from drinking water could be in the range of 5 to 16 g/day

in the dry season, compared to 0.6–1.2 g/day in the rainy season.

Sodium salts are found in virtually all food (the main source of daily exposure) and drinking water. On

the basis of existing data, no firm conclusions have been drawn concerning the possible association

between sodium in drinking-water and the occurrence of hypertension. Therefore there exists need for

evidence that would allow us either to show or reject the notion of association between sodium/salinity

in drinking-water and the occurrence of elevated blood pressure or hypertension.

Is blood pressure higher among population/individuals having high sodium/salinity in drinking-water?

Dependent variable: SBP, DBP, MAP

Independent variable: Salinity/ sodium in drinking water.

Confounders:  Age, sex, body mass index, social class, room temperature, taking anti-hypertensive medication and smoking status

Cross sectional study with reference group.

Populatuion: School children / Adeloscents/ All age group

Extensive baseline interviews will be conducted to collect information on history of drinking water

sources, demographics, and lifestyle characteristics. Dietary intakes of salt will be assessed through

appropiate food-frequency questionnaire (FFQ). In addition, trained physicians administered a

comprehensive anthropometric assessment and blood pressure measurements would be taken.

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