Conference Coverage

Vitamin D did not reduce progression to type 2 diabetes in D2d trial



– Vitamin D supplementation failed to significantly reduce the risk of progression from prediabetes to type 2 diabetes, according to the landmark D2d study.

Dr. Anastassios G. Pittas, Co-Director, Diabetes and Lipid Center; Professor, Tufts University School of Medicine, Boston, Mass.

Dr. Anastassios G. Pittas

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” (World J Diabetes. 2016 Mar 10; 7(5): 89–100).

However, as the report noted, “evidence regarding vitamin D levels and DM is contradictory, and well controlled studies are needed.”

For the D2d study, 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.

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