Are you getting enough Vitamin D?
Vitamin D metabolism
The Daily Value recommended by the Food and Drug Administration (FDA) for Vitamin D for adults is 10 micrograms per day which is 400 International Units (IU) per day. The current recommendations from the Institute of Medicine call for 200 IU/day from birth through age 50, 400 IU for those aged 51 to 70, and 600 IU for those over 70 years. These recommendations were established by determining the level of Vitamin D that was enough to prevent bone demineralization or rickets. Recent studies have determined that these values may be too low.
Although Vitamin D occurs in some foods, Vitamin D is called the sunshine vitamin because it is created from cholesterol in the skin through the action of ultraviolet rays from the sun. The fear of getting skin cancer by exposure to the sun, the widespread use of sunscreen lotions, and the migration of darkly complexioned people to northern latitudes have all combined to decrease the levels of Vitamin D in the blood of the general population, specially in the winter when the days are short. Deficiency in Vitamin D causes weaker bones which break more easily and accelerate the onset of osteoporosis.
Randomized trials using the currently recommended intakes of 400 IU of Vitamin D/day have shown no appreciable reduction in fracture risk. In contrast, trials using 700-800 IU Vitamin D/day found less fracture incidence, with and without supplemental calcium. The safe tolerable upper intake level for Vitamin D is 10,000 IU/day. Adults should be consuming at least 1000 IU per day of Vitamin D to maintain blood serum levels that are effective for strengthening the bones.
 Reinhold Vieth, et al, The urgent need to recommend an intake of vitamin D that is effective, American Journal of Clinical Nutrition, Vol. 85, No. 3, 649-650, March 2007
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