Vitamins

dr.basima s.jaff

1 – Introduction

The term vitamin was introduced in 1911 , and the first vitamin discovered and isolated in a pure crystalline form was effective in preventing and curing a dietary deficiency disease called [polyneuritis].

The name vitamin was proposed for this compound because of its vital need in the preventing and curing of the above pathological condition and because chemically it was found to be an amine .

Now a days ,the term vitamin is used to a group of biologically essential organic chemical compounds have no chemical resemblance to each other ,but because of a similar general function in metabolism.

Generally ,the vitamins can not be synthesized by man

and most other animals and they must be supplied in the diet

, however ,no single food is a rich source of all vitamins .

Before the chemical structures of the vitamins were

known ,they were identified by letters of alphabete .This

system is gradually being replaced by a nomenclature based

on the chemical nature of the compound or a description of

its source or function .

Vitamins are usually needed in small amounts for

normal growth ,development and maintenance of health

.Inside the human body ,vitamins undergo biotransformation

and converted to more complex compounds [co-enzymes]

that playa key role in many cellular reactions .

The average daily requirement for vitamins differs from

one vitamin to another and its influenced by age

,sex[gender], pregnancy, lactation, physical stress and

nutritional state.

II –Hypovitaminosis [vitamins deficiency] -Avitaminosis

Lack of one or more vitamins produces characteristic syndromes and generally .hypovitaminosis is divided into two principal types :

I - Primary hypovitaminosis -

This results from deficient intake or deficiency of the vitamin[s] in the diet .

2- Secondary [conditioned] hypovitaminosis

This arises not because of a lack of vitamin[s] in the diet ,but because of:

1. Decreased [inadequate] intake :such as those occur in

cases of: prolonged vomiting, loss of teeth ,long

standing organic diseases-------etc.

2. Decreased[inadequate] absorption : such as those occur

in cases of malabsorption [diarrhea ,biliary obstruction

and intestinal diseases].

3. Impaired [inadequate]utilization when the vitamin[s] are

not used properly.

4. Increased elimination :such as those occur in cases of

diarrhea . diuresis ,lactation and blood loss .

5. Increased requirement :certain vitamins are needed in

excess in cases of growth ,pregnancy ,lactation ,wound

healing ,excess alcohol consumption and diet rich in

carbohydrates .

6- Faulty bacterial synthesis:The biosynthesis of

certain vitamins which are made up by certain

intestinal bacteria is inhibited ,when antibiotics are

used ..

7- Bacterial destruction :such as decomposition of

vitamin c by intestinal bacteria .

8- Inadequate conversion of the pro vitamin into active

vitamin .

9- Vitamin inhibitors[antagonists] :such as PABA and

Sulphonamides ,Thiaminase present in raw fishes

that hydrolyzes vitamin B1 .

10- Imbalance :its known that is necessary to make a

balnce between water and fat soluble vitamins.

11- therapeutic diet [total parenteral nutrition ] : when

therapeutic diet is used for long periods ,there will he

vitamin deficiency such as glucose saline .

12. Chronic alcoholism for example alcohol inhibits

intestinal absorption. of Vit.B1 causing it's deficiency .

Hypovitaminosis of any type if prolonged, leads to

avitaminosis ,which is characterized by :

1. A gradual decrease in tissue level of vitamins .

2. Biochemical lesions .

3. Anatomic lesions .

4. Cellular pathology [diseases].

5. Death .

III –Hyper vitaminosis

Generally ,fat soluble vitamins are more storable in

human body ,so excessive intake can result in toxic

conditions .However ,with the exception of vitamins A,D

and E ,there is little danger of toxic manifestations from the

usual amount of vitamins ,present , either in the diet or in

the ordinary vitamin supplements ,for example : The

minimum lethal dose for Niacin is 6 G./Kg. body wt./day, so

for a person of 60 Kg body wt. this is equal to 6*60=360

G/day ,no one takes this quantity .

IV-Biosynthesis of vitamins

Generally ,the vitamins can not be synthesized by man

and most other animals and they must be supplied in the

diet ,however, certain vitamins are synthesized to greater

or less extent in the human body :

1- This may occurs as a result of bacterial growth in the

intestinal tract .for example bacteria produce considerable

amounts of vitamins K2,B5, B7 and B 12 .

2- Metabolic biotransformation of the essential amino acid

[tryptophan] to niacin .

3- Vitamin D3 may be synthesized from cholesterol by the

skin ,if its properly exposed to adequate sun shine

VII-Classification of vitamins:

1 - Fat soluble vitamins :this group includes :vitamins A,D,E

and k ,they are usually associated with the lipids of natural

foods .

2- Water soluble vitamins :vitamin C and B complex vitamins

.

1 - Fat soluble vitamins

1- Vitamin A

1 - Properties : soluble in fat and fat solvents discovered in

1913 , stable at high temperature ,destroyed by U.V. light,

found either as vitamin A or as its precursor which is

called pro vitamin A or Beta-carotene ,which is converted

after its absorption to vit. A in the intestinal wall and liver .

2- Chemistry : vit.A is a complex primary alcohol,the terminal

[OH] group is esterified mostly with palmitic acid [C16 :0]

,its structural formula is characterized by the presence of

beta ionone ring .

There are two principal types of vit.A :

1-Vit.Al or Retinol = Retinal

2-Vit.A2 or 3-dehydroretinol ,which has a potency of 40% of

that of vit.Al and its structural formula differs from that of

vit.A1 , only in the presence of an additional double bond

between C3 and C4 in the beta ionone ring .

Vit.Al may be derived from beta-carotene by cleavage

of the chain in a dioxygenase reaction in the presence of

oxygen yielding two molecules of vit.Al .

5- Physiologic roles : Includes :

I -Vit.A has antioxidant property,so it has an important role in

preventing certain . types of cancer ,mainly lung cancer .

2-maintenance of epithelial tissues .

3-Promotes the formation of skeleton, so its important for

growth

4-Vit.A is necessary for reproduction and lactation .

5-Certain derivatives of vit.A are used for the treatment of

acne and psoriasis .

6-It has a specific role in the physiologic mechanism of vision

[its involved in optic nerve transmission] .

Rhodopsin opsin + Retinal

protein part non protein part

visual purple,

retinal pigment, photoreceptor molecule,conjugated protein

found in rode and cone cells of the retina of the eyes

When light stricks on the rode and cone cells of the

retina of the eyes which contains Rhodopsin ,the latter is

coverted to opsin and retinol . Normally ,equilibrium is

maintained in the retina of the eyes such that the rate of

breakdown of rhodopsin is equaled by the rate of

regeneration . When there is deficiency of vit.A,the rate of

rhodopsin regeneration is retarded ,and this affects the

process of vision and the patient may be a night blind

[Nyctalopia] .

7-Hypovitaminosis A : this may be either primary or

secondary and characterized by :

1 -Slowing or stopping of growth in young animals .

2-Avoidance of light[photophobia],and [xerophthalmia] which

is characterized by drying of the eyes ,the cells of the

lacrimal glands become keratinized and stop secreting

tears, this may cause blidness if its not treated .

3-Vit.A deficiency has similar effects on the other epithelial

tissues, mainly those of the respiratory and alimentary

tracts .

4-Vit.A deficiency lowers body resistance against bacterial

infections .

5-It causes nyctalopia .

6-There will be deposition of carotene in the skin .

7-There are also dryness and scaliness of the skin .

8-Vit.A deficiency leads to the formation of urinary caculi .

9-There is a defective in the formation of the enamel of the

teeth .

10-VitA deficiency causes paralysis and nerve degeneration .

11 -There will be atrophy of the testis .

12-Vit. A deficiency causes also a delay of wound healing .

13-The risk of cancer is increased

8-Hypervitaminosis :

ingestion of an excess of vitA causes :

1 -Anorexia[loss of appetite] .

2-Irritability[bone pain] .

3-Fissuring at the corner of the mouth .

4-Cracking and bleeding of the lips .

5-Loss of hair .

6-Hepatosplenomagaly and liver damage .

7-Headache and muscle stiffness .

8-Abortion.

9-Menstrual irregularities

9-Recommended Dietary Allowance [RDA] :

It varies according to age, individual condition, sex

and .and normally its :

4000 I.U. for women . 5000 I.U. for men. This quantity must be

increased to 6000 I.U./day in cases of lactation and

pregnancy .

lUg. = 3 I.U.

Vitamin D

Vitamin D =Steroid pre[o]-hormone = Anti-rachitic vitamin

=Calciol= Calcitriol = sun shine Vitamin.

1- Properties : Vit. D is a white crystalline compound ,soluble

in fat and fat – solvents ,discovered in 1933 . Vitamins D

are a group of compounds that are sterols occurring in

nature, principally in animal organisms .

Certain of these sterols are pro-vitamin D , and when

subjected to long wave U.V. light acquire the physiologic

properties of preventing and curing [Rickets] a disease

Characterized by skeletal abnormalities including failure of

calcification

2- Chemistry : For nutritional purposes the two principal D

vitamins are : -

• Vit. D2 [activated Ergosterol] or Ergocalciferol or Viosterol

,which is of vegetable origin.

• Vit. D3 [activated 7-dehydrocholesterol] or cholecalciferol

,which is of animal origin. .

Man and other mammals can synthesize pro-vit. D3 in their

bodies .Both vitamins D2 and D3 have equal potencies .

3- Occurrence : Vitamins D are found mainly in : cod liver

oi1,other fish oils. eggs ,liver ,milk ,mush rooms and

cereals

5-Physiologic roles : includes :

1-Vit. D increases the intestinal absorption of Ca and P .

2-It has a direct effect on calcification process .

3-It affects the clearance and excretion of P by the kidneys .

4-Its also essential for normal Insulin secretion ,cell

differentiation and immunity .

6-Hypovitaminosis : its characterized by :

1-Rickets in children and Osteomalacia in adult .

2-An increase in the level of serum alkaline phosphatase .

3-A delay in dentition in children .

4-Hypoplasia [poor structural development] .

7-Hypervitaminosis : ingestion of an excess of vit.D causes :

1 -Anorexia and weakness .

2-Nausea and headache .

3-Digestive disturbances[constipation] and polyuria .

4-Irreversible damage of kidneys .

5-Calcification of soft tissues .

6-Hypercalcuria ,resulting in kidney stones .

8-RDA : varies according to age,sex and individual conditions

and normally its about : 2.5 Mg. in adult and 10 Mg. in

infant ,children ,pregnant and nursing women .lUg.= 10 I.U.

Vitamin E = Alpha tocopherol

1-Properties : fat soluble vit.,soluble in fat and fat solvents

,known also as anti-sterility vit Or fertility factor

,discovered in 1922 . The name tocopherol is a Greek

word-means Child-bearing plus an oL for an alcohol .

2-Chemistry : There are several tocopherol isomers ,like

alpha ,beta ,gamma ,delta----etc., of which the alpha isomer

is the most potent and it has the following structural

formula :

PUFA-H = polyunsaturated fatty acid

PUFA-OO•= peroxyl radical of polyunsaturated fatty acid

PUFA-OOH = hydroxyperoxy polyunsaturated

fatty acid PUFA-OH = hydroxy polyunsaturated fatty acid

Free radical

chain reaction

Interaction and synergism between antioxidant

systems operating in the lipid phase (membranes) and

the aqueous phase (cytosol)

3- Occurrence: good sources of vit E are eggs ,muscle ,liver,

fish .chicken ,oat meal ,corm oil ,Soya ,cotton seeds and

wheat germ oils

4-physiological roles :

1. Vit.E prevents auto-oxidation[ peroxidation] of

polyunsaturated fatty acids,so it can be used as an anti -

oxidant .

2. It prevents damage of lung tissues caused by various

oxidants found in the air

3. Vit. E serves as a co-factor in electron transfer system .

4. Its essential for normal immune system .

5-Hypovitaminosis : its characterized by:

1 - Resorption of the foetus in females .

2 – Atrophy of the spematogenic tissues and permanent

sterility in males ,

3-RBC haemolysis and anemia .

4-Abnormal metabolism of nucleic acids .

5-An increase in urinary excretion of creatine .

6-Steatorrhea ,cystic fibrosis and pancreatitis .

6-Hpervitaminosis : its characterized by :

malaise and fatigability .

RDA : It varies according to age,sex,individual conditions and

the amount of P.U.S.F.A in the diet .

[vit.E/P.U.S.F.A.]= 0.6 . Normally its about 10 Mg./day .

1 I.U. =0.67Mg. Tocopherol .

Vitamins K:

Chemistry : a large number of chemical compounds which

are related to 2-methyl-1,4 naphthoquinone posses some

degree of vit.K activity .The principal types of vit.K are :

1 - Vit. K1= Mephyton = Phytonadione =Phylloquinone = 2-

methyl-3-phytyl 1,4- naphthoquinone,this type of vit.K is of

plant origin .

2- Vit.K2 =Menaquinone =Farnoquinone =2-methyl-3-

difamesyl 1,4naphthoquinone,it occurs as a metabolic

product of intestinal bacteria as well as in animal tissues

3- Vit.K3 -Menadione = 2-methyl-1,4 –naphthoquinone ,is a

synthetic compound .This suggested that this portion[2-

methyl 1,4-naphthoquinone] of the molecule is essential for

biologic effects .

Physiological Effects of Vitamin K

•Vitamin K serves as an essential cofactor for a

carboxylase that catalyzes carboxylation of glutamic

acid residues on vitamin K-dependent proteins. These

proteins are involved in:

1) Coagulation2) Bone Mineralization

3) Cell growth

4- Occurrence : vit.K is found mainly In : liver,G.I.T., skeletal

muscles ,cows milk, cheese ,kale, cabbage , cauliflower

,alfalfa,peas, and cereals .

5-Physiologic roles : include :

1 -Vit.K catalyzes the biosynthesis of several plasma clotting

factors such as factors :11 [prothrombin]. V11,1X and X .

2-It catalyzes the oxidative phosphorylation .

3-It induces RNA formation .

4-VitK has an important role in Ca metabolism .

5-It may be used as anti-dote for anti-coagulant drugs such

as coumarine derivatives .

6-It has also an important role in mineralization process .

6-Hypovitaminosis : its characterized by :

1-Episiaxis and excessive menstrual loss .

2-Haematuria .

3- G.I.T. harmorrhage .

4-Hypoprpothrombinemia .

7-Hypervitaminosis :its characterized by :

1 -Hyperbilirubinemia and haemolytic anemia .

2-Liver damage .

3-Reduced effectiveness of anti-coagulants