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vitamin D
term used for either of two active substances required for the body to use calcium and phosphorus, two elements that are essential for the growth and maintenance of bone. Ergocalciferol is sometimes called vitamin D2, and cholecalciferol is sometimes called vitamin D3. The action of sunlight on the skin changes certain substances n the body into vitamin D. Deficiency of the vitamin, most
often by lack of exposure to sunlight, causes rickets in children and osteomalacia and osteoporosis in adults. Few foods contain vitamin D; the only rich natural sources are fish liver oil and the livers of animals that feed
on fish. For this reason vitamin D often is added to milk. A toxic syndrome called hypervitaminosis D can result from intake of too much vitamin D.
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