Vitamin D: endogenous synthesis, hormonal actions, and deficiency
THE CONTEXT
Vitamin D is not strictly a vitamin because it can be synthesized in the skin, which supplies most vitamin D under most conditions.
Source and dietary dependence
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Skin synthesis is normally the major source of vitamin D; a dietary source is required when sunlight exposure is inadequate.
Functions and mechanism
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The main function of vitamin D is regulation of calcium absorption and homeostasis.
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Most actions are mediated through nuclear receptors that regulate gene expression.
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Vitamin D also regulates cell proliferation and differentiation.
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The source describes evidence that intakes considerably above those required for calcium homeostasis reduce the risk of insulin resistance, obesity, metabolic syndrome, and various cancers.
Deficiency
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Vitamin D deficiency causes rickets in children and osteomalacia in adults.
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Deficiency remains a problem in northern latitudes, where sunlight exposure is inadequate.