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Does Vitamin D Supplementation Lower Diabetes Risk?

August 14, 2019

Researchers recently sought to understand how vitamin D3 supplementation impacted diabetes risk among patients at high risk for the disease. According to their findings, published online in the New England Journal of Medicine, they found that supplementation at a dose of 4000 IU per day did not significantly lower disease risk.

“Observational studies support an association between a low blood 25-hydroxyvitamin D level and the risk of type 2 diabetes,” explained Anastassios Pittas MD, of Tufts Medical Center, and colleagues. “However, whether vitamin D supplementation lowers the risk of diabetes is unknown.”

For the study, Dr Pittas and colleagues enrolled adults who had no diagnostic criteria for diabetes and adults who met at least 2 of 3 glycemic criteria for prediabetes, including 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%. The participants were randomly assigned to receive 4000 IU per day of vitamin D3 or placebo regardless of the baseline serum 25-hydroxyvitamin D level.

Based on the enrollment criteria, 2423 participants underwent randomization, including 1211 to the vitamin D group and 1212 to the placebo group.

“The primary outcome in this time-to-event analysis was new-onset diabetes, and the trial design was event-driven, with a target number of diabetes events of 508,” the research team explained.

According to the study findings, the mean serum 25-hydroxyvitamin D level in the vitamin D group was 54.3 ng per milliliter from 27.7 ng per milliliter at baseline and 28.8 ng per milliliter in the placebo group from 28.2 ng per milliliter at baseline at 24 months. Further findings show that the primary outcome of diabetes occurred in 293 participants in the vitamin D group and 323 in the placebo group after a median follow-up of 2.5 years. Finally, the incidence of adverse events was not significantly different between both study groups.

“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,” concluded Dr Pittas and colleagues.

Julie Gould  


Pittas AG, Dawnson-Hughes B, Sheehan P, et al. Vitamin d supplementation and prevention of type 2 diabetes [published online August 8, 2019]. N Engl J Med. 2019; 381:520-530
doi: 10.1056/NEJMoa1900906

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