Controversies in medicine: the role of calcium and vitamin D supplements in adults.

Vitamin D is made in the skin when exposed to sunlight, so deficiency is usually the result of low sunlight exposure (eg, in frail older people and in individuals who are veiled). Calcium and/or vitamin D supplements have been used for the prevention and treatment of osteoporosis. The major trials in community-dwelling individuals have not demonstrated fracture prevention with either calcium, vitamin D, or their combination, but the results of a large study in vitamin D-deficient nursing home residents indicated a reduced fracture incidence. Trials show that vitamin D increases bone density when winter 25-hydroxyvitamin D levels are below 25-30 nmol/L. However, assay expense and variability suggest that supplements are better targeted based on clinical status to frail older people and possibly to people with dark skin living at higher latitudes. A daily dose of 400-800 units (10-20 μg) is usually adequate. Parenteral antiresorptive drugs can cause hypocalcaemia in severe vitamin D deficiency (< 25 nmol/L), which should therefore be corrected before treatment. Clinical trials have not demonstrated benefits of vitamin D on non-skeletal endpoints. Calcium supplements in healthy individuals are not needed, nor are they required in most people receiving treatment for osteoporosis, where they have not been shown to affect treatment efficacy. Calcium supplements cause constipation, bloating and kidney stones, and some evidence suggests they may cause a small increase in the risk of myocardial infarction. Low dose vitamin D is safe, but high doses result in more falls and fractures. Current evidence does not support the use of these supplements in healthy community-dwelling adults.