Brief Review

Vitamin D Deficiency in the Southern United States

Authors: Vin Tangpricha, MD, PhD


Vitamin D is an essential nutrient for optimal calcium homeostasis for the body. Vitamin D is a secosteroid hormone (“seco” meaning “cut”) with two forms: D2 found in the diet, and D3, which is either found in the diet or made in the skin from 7-dehydrocholesterol (7-DHC) upon exposure to ultraviolet B radiation (UVB) between wavelengths of 290 and 315 nm. Upon entering the circulation, vitamin D (D without subscripts refers to either D2 or D3) undergoes two sequential hydroxylations. The first hydroxylation occurs in the liver in the 25 position to form 25-hydroxyvitamin D (25(OH)D), the major circulating form of vitamin D with a half-life of 2–3 weeks. The second hydroxylation happens in the kidney in the 1 position to create 1,25(OH)2D, the active form. The major role of vitamin D is to maintain adequate serum calcium and phosphorus levels for proper mineralization of bone by increased intestinal efficacy of calcium and phosphorus absorption from the small intestine.

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