Vitamin D Supplementation: Can It Prevent Diabetes?

Vitamin D supplementation is not associated with a lower risk of type 2 diabetes in individuals at high risk for type 2 diabetes who do not have vitamin D insufficiency, according to the results of a recent study.

While previous studies have suggested that lower blood 25-hydroxyvitamin D levels are associated with the risk of type 2 diabetes, whether supplementation could affect this association is still unknown.

For their study, the researchers randomly assigned 2423 adults who met at least 2 of 3 glycemic criteria for prediabetes (fasting plasma glucose level, 100 to 125 mg per deciliter; plasma glucose level 2 hours after a 75-g oral glucose load, 140 to 199 mg per deciliter; and glycated hemoglobin level, 5.7 to 6.4%) to either 4000 IU per day of vitamin D3 (n = 1211) or to placebo (n = 1212). Randomization occurred without consideration of baseline serum 25-hydroxyvitamin D level.

After a median follow-up of 2.5 years, diabetes was observed in 293 participants in the vitamin D group and 323 in the placebo group, equating to 9.39 and 10.66 events per 100 person-years, respectively. The hazard ratio for diabetes in the supplementation group was 0.88 (0.95% confidence interval, 0.75 to 1.04; P=0.12).

“Among persons at high risk for type 2 diabetes not selected for vitamin D insufficiency, vitamin D3 supplementation at a dose of 4000 IU per day did not result in a significantly lower risk of diabetes than placebo.”

—Michael Potts


Pittas AG, Dawson-Hughes B, Sheehan P, et al. Vitamin D Supplementation and Prevention of Type 2 Diabetes [published online June 7, 2019]. NEJM. DOI: 10.1056/NEJMoa1900906.