The program focuses on the role of vitamin D in prevention and treatment of type 2 diabetes (vitamindfordiabetes.org). The program is funded by NIH and ADA to conduct observational and randomized trials on prevention of type 2 diabetes. We have completed a large multi-center trial on vitamin D supplementation for prevention of type 2 diabetes (www.d2dstudy.org) and recently completed a second smaller 2-site trial on vitamin D supplementation for treatment of established type 2 diabetes. Tufts Medical Center also served as a clinical site for both trials.