Vitamin D is a fat-soluble vitamin that is naturally present in very few foods, added to others, and available as a dietary supplement. It is also produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis. Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and to prevent hypocalcemic tetany. Vitamin D prevents rickets in children and osteomalacia in adults. Together with calcium, vitamin D also helps protect older adults from osteoporosis.
Vitamin D has other roles in the body, including modulation of cell growth, neuromuscular and immune function, and reduction of inflammation. Many genes encoding proteins that regulate cell proliferation, differentiation, and apoptosis are modulated in part by vitamin D. It has many positive influences and greatly boosts the immune system (more specifically CD8+ T lymphocytes) possibly preventing mesothelioma and other cancers.
There is considerable discussion of the serum concentrations of vitamin D associated with deficiency (e.g. rickets), adequacy for bone health, and optimal overall health, and cut points have not been developed by a scientific consensus process. Recommended Dietary Allowance (RDA) (average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy people) recommends about 15 mcg/day. And the Tolerable Upper Intake level (UL) (maximum daily intake unlikely to cause adverse health effects) is 100 mcg/day for adults.
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