Author
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Dawson-Hughes, Bess |
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Submitted to: American Society for Bone and Mineral Research
Publication Type: Book / Chapter Publication Acceptance Date: 3/17/2006 Publication Date: 7/15/2006 Citation: Dawson-Hughes, B. 2006. Calcium and Vitamin D. In: Favus MJ. Book Chapter. Sixth Edition. Washington, D.C.: American Society for Bone and Mineral Research. p.257-259. Interpretive Summary: Technical Abstract: This chapter describes the roles of calcium and vitamin D in bone health. Calcium is required for the bone formation phase of bone remodeling and it also affects bone mass through its impact on the remodeling rate. Typically, about 5 nmol (200 mg) of calcium is removed from the adult skeleton and replaced each day. An inadequate intake of calcium results in reduced calcium absorption, a lower circulating ionized calcium concentration, and an increased secretion of PTH, a potent bone-resorbing agent. A high remodeling rate leads to bone loss and it is also an independent risk factor for fracture. With aging, there is a decline in calcium absorption efficiency in men and women, which may be related to loss of intestinal vitamin D receptors or resistance of these receptors to the action of 1,25(OH)D. Vitamin D is acquired from diet and from skin synthesis on exposure to UV B rays, and diet composition, season, and race also influence calcium absorption efficiency. The best clinical indicator of vitamin D status is the serum 25-hydroxyvitamin D [25(OH)D] level. Those levels decline with aging for several reasons. There is less efficient skin synthesis of vitamin D with aging as a result of age-related decline in the amount of 7-dehydrocholesterol, the precursor to vitamin D, in the epidermal layer of skin. Also, older individuals as a group spend less time outdoors. There does not seem to be an impairment in the intestinal absorption of vitamin D with aging. |
