The most common nutritional deficiency worldwide, characterized by serum 25-hydroxyvitamin D <20 nanograms/mL. Vitamin D insufficiency is regarded as a serum 25-hydroxyvitamin D level between 21 and 29 nanograms/mL.
Main causes include sun avoidance, using sun protection, increased skin pigmentation, inadequate dietary and supplemental vitamin D intake, malabsorption syndromes, obesity, and medication use.
Acquired and inherited disorders that either reduce or prevent the metabolism of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D also present with biochemical and skeletal abnormalities seen with vitamin D deficiency, but in a more severe form.
Most patients are asymptomatic. Severe prolonged vitamin D deficiency causes growth retardation and rickets in children and osteomalacia, osteopenia, and osteoporosis in adults.
Both vitamin D deficiency and vitamin D insufficiency are corrected by giving vitamin D2 or vitamin D3 in treatment doses followed by lifelong maintenance doses; adequate sensible sunlight exposure should be encouraged.
Additional replacement with 1,25-dihydroxyvitamin D or one of its active analogs is necessary for those with disorders of vitamin D metabolism.
Chemical structure of vitamin D
From the collection of M.F. Holick, PhD, MD; used with permission