What You and Your Patients Need to Know About Vitamin D

“Vitamin D” is the term commonly used to denote the lipid-soluble hormone critical for
calcium homeostasis and skeletal maintenance. A precursor to the active compound is
found in many plants and animal tissues and can be absorbed from the gut; it can also be
derived from cell membranes in the epidermis during ultraviolet B irradiation. This compound
is then hydroxylated sequentially in the liver and kidney to produce the active
hormone 1,25(OH)2D that binds its nuclear receptor to modulate gene expression. Recently,
vitamin D hydroxylases and the nuclear receptor have been identified in many
tissues, suggesting previously unrecognized roles for vitamin D. Some epidemiologic
studies have also correlated low levels of the inactive storage form 25(OH)D with an
increased incidence or prevalence of a variety of diseases, suggesting that large oral
supplements and/or increased ultraviolet (UV) exposure might therefore improve individual
health. However, randomized, prospective controlled trials comparing vitamin D supplements
with placebo have not supported this belief. Moreover, current evidence supports
the conclusion that protection from UV radiation does not compromise vitamin D status or
lead to iatrogenic disease. In contrast, high vitamin D levels appear to incur a risk of kidney
stones and other adverse effects. In the case of true vitamin D deficiency, supplements are
a more reliable and quantifiable source of the vitamin than UV exposure.
Semin Cutan Med Surg 31:2-10 © 2012 Elsevier Inc. All rights reserved.

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