Effects of Combined Calcium and Vitamin D Supplementation on Insulin Secretion, Insulin Sensitivity and b-Cell Function in Multi-Ethnic Vitamin D-Deficient Adults at Risk for Type 2 Diabetes: A Pilot Randomized,

Objectives: To examine whether combined vitamin D and calcium supplementation improves insulin sensitivity, insulin secretion, b-cell function, inflammation and metabolic markers. Design: 6-month randomized, placebo-controlled trial. Participants: Ninety-five adults with serum 25-hydroxyvitamin D [25(OH)D] #55 nmol/L at risk of type 2 diabetes (with prediabetes or an AUSDRISK score $15) were randomized. Analyses included participants who completed the baseline and final visits (treatment n = 35; placebo n = 45). Intervention: Daily calcium carbonate (1,200 mg) and cholecalciferol [2,000–6,000 IU to target 25(OH)D.75 nmol/L] or matching placebos for 6 months. Measurements: Insulin sensitivity (HOMA2%S, Matsuda index), insulin secretion (insulinogenic index, area under the curve (AUC) for C-peptide) and b-cell function (Matsuda index x AUC for C-peptide) derived from a 75 g 2-h OGTT; anthropometry; blood pressure; lipid profile; hs-CRP; TNF-a; IL-6; adiponectin; total and undercarboxylated osteocalcin. Results: Participants were middle-aged adults (mean age 54 years; 69 % Europid) at risk of type 2 diabetes (48 % with prediabetes). Compliance was.80 % for calcium and vitamin D. Mean serum 25(OH)D concentration increased from 48 to 95 nmol/L in the treatment group (91 % achieved.75 nmol/L), but remained unchanged in controls. There were n