The use of vitamin D supplements to prevent and treat a wide range of illnesses has increased substantially over the last decade. Epidemiologic evidence links vitamin D deficiency to autoimmune disease, cancer, cardiovascular disease, depression, dementia, infectious diseases, musculoskeletal decline, and more.

The Institute of Medicine published an exhaustive report in 2010 that concluded that vitamin D supplementation for indications other than musculoskeletal health was not adequately supported by evidence and that most North Americans receive sufficient vitamin D from their diet and sun exposure. These conclusions are at odds with some clinical practice guidelines; thus, we sought to summarize the best available evidence regarding the benefits of vitamin D supplementation, to examine the potential risks, and to provide practical dosing advice.

The adequacy of vitamin D stores is determined by measuring the 25-hydroxyvitamin D serum concentrations. The demarcations between deficiency (< 20 ng/ml), insufficiency (20-30 ng/ml), and optimal (30-80 ng/ml) serum concentrations are controversial. Vitamin D in doses of 800-5000 IU/day improve musculoskeletal health (e.g., reduces the rate of fractures and falls in older adults (aged ≥ 65 yrs). In patients with documented vitamin D deficiency, a cumulative dose of at least 600,000 IU administered over several weeks appears to be necessary to replenish vitamin D stores. Single large doses of 300,000-500,000 IU should be avoided. Vitamin D supplementation should not be offered routinely to other patient populations.

Although results from some prospective clinical trials are promising, most have not been robustly designed and executed. The decision by young, otherwise healthy adults to take vitamin D in doses of 2000 IU/day or lower is unlikely to cause harm.

For patients who are not at risk for developing vitamin D deficiency, sensible sun exposure is an inexpensive and enjoyable way to maintain vitamin D stores.