vitamin D

vitamin D
a fat-soluble vitamin that enhances the absorption of calcium and phosphorus from the intestine and promotes their deposition in the bone. It occurs in two forms: ergocalciferol (vitamin D2, calciferol), which is manufactured by plants when the sterol ergosterol is exposed to ultraviolet light, and cholecalciferol (vitamin D3), which is produced by the action of sunlight on 7-dehydrocholesterol, a sterol widely distributed in the skin. A deficiency of vitamin D, either from a poor diet or lack of sunlight, leads to decalcified bones and the development of rickets and osteomalacia. Good sources of vitamin D are liver and fish oils. The recommended daily intake is 10 μg for a child up to five years and 2.5 μg thereafter. Vitamin D is toxic and large doses must therefore be avoided.

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