Effects of Vitamin D Supplementation on Insulin Sensitivity and Secretion in Prediabetes
Neda Rasouli, Irwin Brodsky, Ranee Chatterjee, Sun H. Kim, Richard E. Pratley, Myrlene A. Staten, Anastassios G. Pittas, Anastassios G. Pittas, Irwin Brodsky, Lisa Ceglia, Chhavi Chadha, Ranee Chatterjee, Bess Dawson‐Hughes, Cyrus Desouza, Rowena J Dolor, John P. Foreyt, Adline Ghazi, Daniel S. Hsia, Karen Johnson, Sangeeta R. Kashyap, Sun H. Kim, Erin S. LeBlanc, Michael R. Lewis, Emilia Liao, Saúl Malozowski, Lisa M. Neff, Patrick M. O’Neil, Jean Park, Anne L. Peters, Lawrence S. Phillips, Richard E. Pratley, Philip Raskin, Neda Rasouli, David C. Robbins, Clifford J. Rosen, Dave Reboussin, Vanita R. Aroda, James H. Ware, Patricia Sheehan, Myrlene A. Staten, William C. Knowler
Abstract
CONTEXT: Vitamin D regulates glucose homeostasis pathways, but effects of vitamin D supplementation on β-cell function remain unclear. OBJECTIVE: To investigate the effects of vitamin D3 supplementation on insulin sensitivity and β-cell function. METHODS: This is a prespecified secondary analysis of the Vitamin D and Type 2 Diabetes study. Overweight/obese adults at high risk for type 2 diabetes (prediabetes) were randomly treated with vitamin D3 4000 IU or matching placebo daily for 24 months. MAIN OUTCOME: Disposition index (DI), as an estimate of β-cell function, was calculated as the product of Homeostasis Model Assessment 2 indices derived from C-peptide values (HOMA2%Scpep) and C-peptide response during the first 30 minutes of a 75-g oral glucose tolerance test (OGTT). RESULTS: Mean age was 60.5 ± 9.8 years and body mass index was 31.9 ± 4.4 kg/m2. Mean serum 25(OH)D level increased from 27.9 ± 10.3 ng/mL at baseline to 54.9 ng/mL at 2 years in the vitamin D group and was unchanged (28.5 ± 10.0 ng/mL) in the placebo group. The baseline DI predicted incident diabetes independent of the intervention. In the entire cohort, there were no significant differences in changes in DI, HOMA2%Scpep, or C-peptide response between the 2 groups. Among participants with baseline 25(OH)D level <12 ng/mL, the mean percent differences for DI between the vitamin D and placebo groups was 8.5 (95% CI, 0.2-16.8). CONCLUSIONS: Supplementation with vitamin D3 for 24 months did not improve an OGTT-derived index of β-cell function in people with prediabetes not selected based on baseline vitamin D status; however, there was benefit among those with very low baseline vitamin D status.