Baseline Characteristics of the Vitamin D and Type 2 Diabetes (D2d) Study: A Contemporary Prediabetes Cohort That Will Inform Diabetes Prevention Efforts

OBJECTIVE To describe baseline characteristics of the Vitamin D and Type 2 Diabetes (D2d) study, the first large U.S. diabetes prevention clinical trial to apply current American Diabetes Association (ADA) criteria for prediabetes. RESEARCH DESIGN AND METHODS This is a multicenter ( n = 22 sites), randomized, double-blind, placebo-controlled, primary prevention clinical trial testing effects of oral daily 4,000 IU cholecalciferol (D 3 ) compared with placebo on incident diabetes in U.S. adults at risk for diabetes. Eligible participants were at risk for diabetes, defined as not meeting criteria for diabetes but meeting at least two 2010 ADA glycemic criteria for prediabetes: fasting plasma glucose (FPG) 100–125 mg/dL, 2-h postload glucose (2hPG) after a 75-g oral glucose load 140–199 mg/dL, and/or a hemoglobin A 1c (HbA 1c ) 5.7–6.4% (39–46 mmol/mol). RESULTS A total of 2,423 participants (45% of whom were women and 33% nonwhite) were randomized to cholecalciferol or placebo. Mean (SD) age was 59 (9.9) years and BMI 32 (4.5) kg/m 2 . Thirty-five percent met all three prediabetes criteria, 49% met the FPG/HbA 1c criteria only, 9.5% met the 2hPG/FPG criteria only, and 6.3% met the 2hPG/HbA 1c criteria only. Black participants had the highest mean HbA 1c and lowest FPG concentration compared with white, Asian, and other races ( P 1c and FPG concentrations. CONCLUSIONS The D2d study will establish whether vitamin D supplementation lowers risk of diabetes and will inform about the natural history of prediabetes per contemporary ADA criteria.