Vitamin D

A steroid vitamin which promotes the intestinal absorption and metabolism of calcium and phosphorus. Under normal conditions of sunlight exposure, no dietary supplementation is necessary because sunlight promotes adequate vitamin D synthesis in the skin. Deficiency can lead to bone deformity (rickets) in children and bone weakness (osteomalacia) in adults. Vitamin D comes from the diet (eggs, fish, and dairy products) and is produced in the skin. Skin production of the active form of vitamin D depends 0n exposure to sunlight. Active people living in sunny regions produce most of the vitamin D they need from their skin. In less sunny climes the skin production of vitamin D is markedly diminished in the winter months, especially among the elderly and the housebound. In that population, vitamin D supplements become important. Vitamin D deficiency among the elderly is quite common in the US. In a study of hospitalized patients in a general medical ward, vitamin D deficiency was detected in 57% of the patients. An estimated 50% of elderly women consume far less vitamin D in their diet than recommended. The Food and Nutrition Board of the Institute of Medicine recommended the following as an adequate vitamin D intake: 200 IU daily for people 19-50 years old; 400 IU daily for those 51-70 years old; and 600 IU daily for those 71 years and older. An average multivitamin tablet contains 400 IU of vitamin D. Therefore, taking a multivitamin a day should help provide the recommended amount of vitamin D.

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vitamin D n any or all of several fat-soluble vitamins chemically related to steroids, essential for normal bone and tooth structure, and found esp. in fish-liver oils, egg yolk, and milk or produced by activation (as by ultraviolet irradiation) of sterols: as

a) CALCIFEROL

b) CHOLECALCIFEROL called also sunshine vitamin

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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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either of two fat-soluble compounds with antirachitic activity, or both collectively: cholecalciferol (q.v.), which is synthesized in the skin and is considered a hormone, and ergocalciferol (q.v.), which is the form generally used as a dietary supplement. Dietary sources include some fish liver oils, egg yolks, and fortified dairy products. Deficiency of vitamin D can result in rickets in children and osteomalacia in adults, while ingestion of excess levels can lead to hypercalcemia, mobilization of calcium from bone, and renal dysfunction. References to metabolites of vitamin D may denote those of cholecalciferol, of ergocalciferol, or of both collectively.