Pittas AG, et al. – Given the association between low blood 25-hydroxyvitamin D level and the risk of type 2 diabetes supported in observational studies, researchers investigated whether vitamin D supplementation lowers the risk of diabetes in this study involving 2,423 participants. Overall, the investigators found that people at high risk for type 2 diabetes not selected for vitamin D insufficiency showed no significant reduction in the risk of diabetes with vitamin D₃ supplementation at a dose of 4,000 IU per day vs placebo.

Methods

• The study sample consisted of adults who met at least two of three glycemic criteria for prediabetes (fasting plasma glucose level, 100 to 125 mg/dL; plasma glucose level 2 hours after a 75-g oral glucose load, 140 to 199 mg/dL; and glycated hemoglobin level, 5.7% to 6.4%) and had no diagnostic criteria for diabetes.
• A total of 1,211 participants were randomized to the vitamin D group (4,000 IU per day of vitamin D₃) and 1,212 were randomized to the placebo, regardless of baseline serum 25-hydroxyvitamin D levels.
• New-onset diabetes was assessed as the primary outcome in this time-to-event analysis; the trial design was event-driven, with a target number of diabetes events of 508.

Results

• The vitamin D group had the mean serum 25-hydroxyvitamin D level of 54.3 ng/mL (from 27.7 ng/mL at baseline) by month 24 vs 28.8 ng/mL in the placebo group (from 28.2 ng/mL at baseline).
• Following a median period of 2.5 years, the vitamin D group had diabetes development in 293 participants vs 323 participants in the placebo group (9.39 and 10.66 events per 100 person-years, respectively).
• For vitamin D vs placebo, the hazard ratio was 0.88 (0.95% CI: 0.75-1.04; P=0.12).
• The two groups did not have significant differences in the incidence of adverse events.