Short essay on composition, functions and sources of Vitamin D

Pure vitamin D is first isolated in 1930and is also known as the anti-rachitic vitamin. Vitamin D is a group of complex alcohol compounds but is generally spoken of as one substance. The important active forms of vitamin D of nutritional interest are Vitamin D₂ known as ergocalciferlo and D₃ known as cholecalciferol.

The precursor of vitamin D in the body is pro vitamin i.e. 7 dehydrocholestrol which is found in the skin. This reacts with ultraviolet rays or the sunlight to form cholecalciferol, the active form of Vitamin D.

Composition and properties

Vitamin D is compound of carbon, hydrogen and oxygen; pure vitamin D can be obtained in a crystalline form. It is odorless and soluble in fat. It can also be dissolved in solvents like carbon, tetrachloride, chloroform, ether, alcohol and acetone.

Functions

Vitamin D is required for normal growth in mammals. It increases the calcium and phosphorus absorption from the gastrointestinal tract by making its membranes more permeable to these salts. It improves the calcification of bones by regulating the amount of calcium and phosphorus that is available.

Cereals contain phytic acid and calcium combines with phytic acid in the body to form calcium phytate. This is an insoluble compound and cannot be absorbed by the body. Phytate enzyme hydrolyses the phytic acid hence preventing the formation of calcium phytate. Vitamin D increases the activity of this enzyme. Thus it maximizes the utilization of calcium and phosphorus.

Sources

Food sources rich in vitamin D include liver oils, egg yolk, milk and milk fat, butter, ghee. Common vegetable foods do not contain Vitamin D. Exposure to sunlight provides a cheap way of permitting the production of Vitamin D in the body itself.

Daily Allowances. The recommended allowances of vitamin D are not known. For the present, 200-400 IU of Vitamin D can be taken as a tentative Value the dietary allowance for Indians .This is an arbitrary value. Children do not generally show deficiency of this vitamin if they have enough exposure to sunlight. A dark skin is less efficient than a light skin in synthesizing this vitamin.

Deficiency.

Rickets occur due to vitamin D deficiency. During rickets the calcium and phosphorus level is always low. Bone growth ceases and more severe cases the has already formed may demineralised. This results in clinical changes which are observed by the swelling or bending of the ribs. This condition is known as ‘rachitic rosary’ the long bones increase in width at the ends and they may become curved instead of remaining straight. This leads to ‘knock knees’ bowed legs, curvature of the vertebral column and deformities of the pelvic bones. Softening of the skull, particularly in infants and the delayed closing of the fontanelle is another important feature of the deficiency of this vitamin. The teeth of rachitic children erupt late and degenerate early because of retarded calcification.

The general feature of deficiency, therefore, include retarded growth, lack of vigour, enlarged parathyroid glands, low level of calcium and phosphorus. Premature children have been found to be more susceptible to rickets than normal children.

Deficiency in adults leads to Osteomalacia-a condition in which the bones become fragile so that they are easily susceptible to fractures.

In old age a deficiency of both vitamin D and calcium leads to osteoporsis, a condition in which the bines become porous and break easily.

Renal rickets may also occur during adult life. This is because of metabolic disorder which allows increased leakage of calcium and phosphorus from the kidneys with a resultant Vitamin D deficiency.

Hyper vitaminosis.

This is associated with the extra intake of calcium. Serum calcium increases, the calcium deposited in the soft tissues such as kidneys, heart eye and abdomen. Joints become swollen, stiff and muscular movements become difficult and painful. In such cases, a diet devoid of Vitamin D and low in calcium should be administered.