Effects of vitamin D supplements on bone mineral density: a systematic review and meta-analysis

Introduction
Vitamin D, like calcium, has long been regarded as a fundamental part of the prevention and treatment of osteoporosis. Low vitamin D concentrations result in secondary hyperparathyroidism and accelerated bone loss, although the development of secondary hyperparathyroidism varies, even in patients with severe vitamin D deficiency.1 and 2 Findings from observational studies show inconsistent associations between bone mineral density and vitamin D status,3 and 4 and debate continues regarding optimum concentrations of 25-hydroxyvitamin D for the best possible skeletal health.5 and 6 However, results from meta-analyses of trials of vitamin D alone (ie, not with calcium) failed