vitamin D, a fat-soluble vitamin chemically related to the steroids and essential for the normal formation of bones and teeth and for the absorption of calcium and phosphorus from the GI tract. The vitamin is present in natural foods in small amounts, and requirements are usually met by artificial enrichment of various foods, especially milk and other dairy products, and exposure to sunlight. Ultraviolet rays activate a form of cholesterol in an oil of the skin that is converted to a form of the vitamin in the kidney. The natural foods containing vitamin D are of animal origin and include saltwater fish, especially salmon, sardines, and herring; organ meats; fish-liver oils; and egg yolk. Deficiency of the vitamin results in rickets in children, osteomalacia, osteoporosis, and osteodystrophy. Hypervitaminosis D produces a toxicity syndrome characterized by anorexia, vomiting, headache, drowsiness, diarrhea, and calcification of the soft tissues of the heart, blood vessels, renal tubules, and lungs. Treatment consists of discontinuing the vitamin dosage and initiating a low-calcium diet until symptoms resolve. See also calciferol, vitamin D3.
