The antirachitic properties of vitamin D, the “sunshine vitamin,” are generally well recognized, and the role of vitamin D in calcium and phosphorus homeostasis is well established.1 In the last several decades, many studies have documented nontraditional roles of vitamin D, as well as adverse consequences of vitamin D deficiency for a range of conditions, including bone health, cancer, cardiovascular disease, glucose intolerance, high blood pressure, some infectious diseases, multiple sclerosis, and type 2 diabetes mellitus.2 Except for effects on bone health, which are established in randomized clinical trials,3 the evidence for most of the other potential benefits is generally considered to be less definitive. Nevertheless, an impressive body of in vitro, animal, clinical, and epidemiologic evidence supports the evidence.