Vitamin D

Vitamin D

There are two distinct forms of Vitamin D

Cholecalciferol (Vitamin D₃) is the natural form of the vitamin occurring in foods (Fig. 8.2). It can be formed under the skin from 7 dehydro cholesterol by the influence of sun light (ultra violet (UV) radiation)

Ergo calciferol (vitamin D₂) is a synthetic form of the vitamin which has the same activity as the natural vitamin. It is produced by the UV radiation of ergo sterol, a compound which can be extracted from yeast. This is the form of vitamin which is added to commodities such as margarine and baby foods.

Functions

Vitamin D is necessary for the growth and maintenance of bones and teeth. Vitamin D helps in the absorption of calcium and phosphorus from the small intestine and for the uptake of calcium and phosphorus by the bones and teeth.

Sources

Vitamin D is not widely distributed in nature and the best sources are fish oil, especially liver oil. Milk, butter and egg yolk are the only foods in the ordinary diet that contain vitamin D.

Requirements

It is difficult to make standard recommendations for the dietary requirements of vitamin D since the amount of vitamin D produced in the body by the action of sunlight varies from person to person. Many people may obtain this vitamin from sunlight. It is, however certain that babies and growing children require more vitamin D than adults, due to rapid growth and bone development.

Infants and children - 400 IU / day 

Adults - 200 IU / day

Pregnant and lactating women - 400 IU/day

Absorption and storage

Fat helps in the absorption of vitamin D and bile is essential for its absorption. Vitamin D enters into the general circulation via lymph and stored largely in liver and kidneys.

Deficiency

Children receiving an inadequate supply of vitamin D develop rickets. Calcium and phosphorus are inadequately deposited in the bones. Premature infants are more susceptible to rickets than full term infants. In adults on inadequate supply of vitamin D causes osteomalacia, a condition in which the bones become soft, weak and painful.