Vitamin D is a steroid hormone which function is to promote mineralization of new bone. This is accomplished by increasing calcium and phosphate absorption by the intestine and kidneys, and stimulating osteoclast activity in bone, to promote bone remodeling. These actions are carried out together with parathyroid hormone, which shares many of the effects of vitamin D. Vitamin D can be acquired as an inactive intermediate through diet or by synthesis in the skin. Its physiologically active form is found only after hydroxylation in the kidneys by the enzyme 1-alpha-hydroxylase to 1,25-dihydroxycholecalciferol.
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