Vitamin D

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  • Topic: Vitamin D, Ultraviolet, Sunlight
  • Pages : 2 (687 words )
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  • Published : October 12, 2010
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Vitamin D
Of the four fat -soluble vitamins, vitamin D is the one concerned with efficient calcium and phosphorus absorption. Working with various hormones-- in particular, calcitonin and the parathyroid hormone--vitamin D's primary role is to ensure that calcium and phosphorous are absorbed from the intestinal tract into the bloodstream. There, the vitamin helps maintain concentrations of the two minerals in the right proportions (the amounts of calcium and phosphate in the blood--as well as the ratio between them--help determine normal bone growth). In addition, vitamin D also appears to act in the bones themselves, stimulating them to accept calcium into their bony matrices. Strictly speaking, vitamin D is not one vitamin but is, instead, a group of vitamins--all derived from a parent compound, structurally similar to cholesterol--and it comes in a variety of forms. From a nutritional standpoint, two of these forms are especially important. The first, vitamin D2 (calciferol), is produced when ultraviolet radiation activates a sterol that is present mainly in yeasts and fungi (sterols are fat-like substances in the steroid family). Vitamin D2, rarely seen in nature, is mostly manufactured in the laboratory specifically to be added to infant formulas and other fortified foods. The second form—vitamin D3 (cholecalciferol)—is derived from a sterol present in animal tissues, including those in the human body. In humans, in fact, the sterol is converted into vitamin D on the skin's surface, a process activated by ultraviolet rays from the sun. For this reason, healthy adults, exposed to normal amounts of sunlight, may produce enough vitamin D in their own skin to avoid the need for added dietary sources. As might be expected, the need for vitamin D is substantially greater in childhood. In infants and young children, lack of the vitamin can cause rickets (or rachitis), a bone disorder that results in bowed legs, knock-knees, curved spines and other abnormalities....
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