SAN FRANCISCO – Vitamin D supplementation failed to significantly reduce the risk of progression from prediabetes to type 2 diabetes, according to the landmark D2d study.
There’s a major limitation: The wide majority of participants already had acceptable levels of vitamin D. Still, the intervention “did not significantly reduce the risk [of diabetes],” Anastassios G. Pittas, MD, professor of medicine at Tufts University, said at the annual scientific sessions of the American Diabetes.
Vitamin D supplementation has been a hot topic on a variety of medical fronts. As a 2016 report noted, “low vitamin D levels are also associated with hypertension, cancer, and cardiovascular disease. In addition, diabetes mellitus (DM) and chronic kidney disease (CKD) are also related to vitamin D levels. Vitamin D deficiency has been linked to onset and progression of DM” ().
However, as the report noted, “evidence regarding vitamin D levels and DM is contradictory, and well controlled studies are needed.”
For thestudy, Dr. Pittas and associates tracked 2,423 patients who were considered to have prediabetes, with at least 2 of 3 American Diabetes Association criteria: fasting plasma glucose level of 100-125 mg/dL; plasma glucose level 2 hours after a 75-g oral glucose load of 140-199 mg/dL; and hemoglobin A1c (HbA1c) level of 5.7%-6.4%.
All patients were at least 30 years old with the exception of American Indians, Alaska Natives, Native Hawaiians and other Pacific Islanders who were allowed to be aged 25-30 years. About 22% had low vitamin D levels.
The mean age was 60 years, mean body mass index was 32, 45% were women, and 33% were non-white.
The researchers assigned 1,211 patients to take a once-daily capsule of vitamin D3 (cholecalciferol; 4,000 IU per day); 1,212 received a placebo.
Patients in the vitamin D group greatly boosted their mean serum 25-hydroxyvitamin D levels, from 27.7 ng/mL at baseline to 54.3 ng/mL at 24 months. In contrast, those in the placebo group saw little change, going from 28.2 ng/mL at baseline to 28.8 ng/mL at 24 months.
At a median follow-up of 2.5 years, with 99% of the study participants remaining in the trial, 616 patients developed diabetes (293 in the vitamin D group, 323 in the placebo group).
The risk was lower in the vitamin D group although the difference was not statistically significant. An analysis revealed no benefit from vitamin D in numerous subgroups (race, age, body mass index, latitude-based geographic location, calcium supplement intake, and others).
However, a post-hoc analysis of patients in the vitamin D group with a baseline 25-hydroxyvitamin D level of less than 12 ng/mL found that they appeared to benefit vs. their counterparts on placebo.