Vitamin D is of great interest to the medical and lay communities. Numerous observational studies (often cross-sectional) have examined the association between serum levels of 25-hydroxyvitamin D (25[OH]D) and various conditions. Low levels of 25(OH)D have been associated with increased risk of falls, fractures, cardiovascular disease, colorectal cancer, type 2 diabetes mellitus, depressed mood, cognitive decline, and mortality.1 However, such studies are subject to potential confounding and bias, and whether vitamin D supplementation reduces the risks of acquiring any of these conditions is less clear. Randomized clinical trials (RCTs) have not shown that vitamin D supplementation improves health, except in persons at high risk of falling, for which some studies1-4 have demonstrated a decreased risk of falls. Based on this evidence, the US Preventive Services Task Force5 (USPSTF) and the American Geriatric Society6 recommend vitamin D supplementation for persons who are at high risk of falls.