Vitamin D And Osteoporosis

For more than 60 years, vitamin D has been known to improve intestinal calcium absorption. This action occurs primarily in the duodenum but also to some extent throughout the small and perhaps even the large intestine. Under optimal conditions, most people can obtain their vitamin D requirement from exposure to sunlight, which contains ultraviolet light that penetrates the skin and converts cholesterol precursors to cholecalciferol. Many factors interfere with this process, including aging, an increase in skin pigmentation, use of sunscreen, window glass, pollutants including ozone, latitude, and season of the year. The appreciable variability in dermal production of vitamin D in different patients should be considered in making recommendations about amounts of orally administered vitamin D that should be ingested at any particular time and place to prevent and treat vitamin D deficiency. For biologic activity, vitamin D must be 25-hydroxylated in the liver and then at the 1 position in the kidney to form 1,25-dihydroxyvitamin D, the most active metabolite.