Abstract

Vitamin D is an essential vitamin and hormone, the critical function on bone mineralization of which is well established and accepted. Low vitamin D levels are detrimental to health and should be treated with vitamin D supplementation; however, the definitions of vitamin D deficiency, dose for supplementation, and need for screening, are not as clear. Organizations such as the Institute of Medicine and the Endocrine Society have advocated different laboratory criteria for diagnosing vitamin D deficiency.^1,2 Only a small number of prospective randomized clinical trials on vitamin D supplementation in community-dwelling individuals have been conducted to test whether it reduces the risk of fracture, but the results are not always consistent. Interestingly, there are more meta-analyses of the trials than trials themselves. The US Preventive Services Task Force recommends against daily supplementation with <400 IU of vitamin D₃ and  <1000 mg of calcium for the primary prevention of fractures in community-dwelling postmenopausal women.³ Paralleling the above controversies, numerous risk factor studies have suggested that higher vitamin D levels are beneficial for almost all major human disease categories from cardiovascular disease to cancer. These studies constitute most of the exponentially expanding literature on vitamin D deficiency after 2003. Their alleged benefits of vitamin D may convince some physicians and patients that vitamin D deficiency is the underlying cause of, or at least contributes to, many human miseries, with vitamin D being almost a cure all.