The nutritionally important forms of Vitamin D in man are Calceferol (Vitamin D2) and Cholecalciferol (Vitamin D3) Calciferol may be derived by irradiation of the plant sterol, ergosterol, Cholecalciferol is the naturally occurring (Performed Vitamin D which is found in animal fats and fish liver oils. It is also derived from exposure to UV rays of the sunlight which converts the cholesterol in the skin to vitamin D. Vitamin D is stored in the fat depots.
Daily requirements: The daily requirements of vitamin D are: adults - 2.5 mcg (100 IU); Infants and children - 5.0mcg (200IU); Pregnancy and lactation - 10.0 mcg (400 IU)
(One international unit (IU) of vitamin D = 0.025 mg of calciferol �Cthat is, to convert IU to micrograms, divide by 40).
Sources: Vitamin d is unique because it is derived both from sunlight and foods.
(a) Sunlight: Vitamin D is synthesized by the body by the action of UV rays of sunlight of 7 dehydrocholesterol, which is stored in large abundance in the skin. Exposure to UV rays is critical; these can be filtered off by air pollution. Dark-skinned aces such as Negroes also suffer from this disadvantage because black skin can filter off up to 95 percent of UV rays.
(b) Foods: Vitamin occurs by only in the foods of animal origin. Liver, egg yolk, butter and cheese and some species of fish contain useful amounts. Fish liver oils, although not considered to be a food, are the richest sources of Vitamin d. Human milk has recently been shown to contain considerable amounts of water-soluble vitamin D sulfate. Other sources of vitamin D are foods artificially fortified with vitamin D, such as milk, margarine, vanaspathi and infant foods.
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