Vitamin D is a fat soluble with two chemicals forms, vitamin D2 and vitamin D3. In nature only a few food contain vitamin D, such as fatty fish, liver and egg yolks.
Vitamin D is a generic term of all steroids including vitamin D3 and vitamin D2. Vitamin D3, also known as cholecalciferol, and D2, known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm) through transformation of the precursor, 7 dehydrocholestrol. It is said to be more bioactive. It derived from the precursor 7-dehydrocholestrol.
Vitamin D2 or ergocalciferol is derived from plants and only enters the body via the diet, from consumption of foods such as oily fish, egg yolk and liver.
Vitamin D is absorbed from the diet in the intestinal tract in association with liquids and the presence of the bile slats. Once in the liver, one metabolite 25 hydroxy-vitamin D3 is formed, which is a about four times as active as vitamin D.
Vitamin D deficiency is characterized by inadequate mineralization of the bone. In children, vitamin D deficiency results in rickets, which is deformation of the skeleton including abnormal softness of the skull, enlargement of epiphyses of the long bones and costochondral junction that causes bow legs and knock knees. In adults it manifests as osteomalacia.
Vitamin D (D3 and D2) in physiologic replacement and pharmacologic doses has been used to correct vitamin D depletion in the elderly and to prevent vitamin D deficiency at all ages.
Vitamin D3 and D2