Although the data from published studies have suggested a link between vitamin D and diabetes risk, the evidence to support general supplementation with vitamin D for diabetes prevention does not currently exist because such intervention would be based almost exclusively on observational studies, and interpretation of results from the available trials is hindered by several limitations, including the following: analyses on vitamin D and glycemic outcomes were post hoc, all but two trials were under powered for glycemic outcomes, most trials reported poor adherence to the vitamin D supplementation, and the effect of concurrent diabetes pharmacotherapy on outcomes was rarely reported in studies of participants with established diabetes.