Vitamin D Supplements Do Not Prevent Diabetes Onset

About 84 million Americans have prediabetes, which puts them at significant risk for progressing to type 2 diabetes. Several lifestyle changes—such as weight loss and exercise—could reduce this risk. However, the use of vitamin D supplements may not be a beneficial change, according to research presented at the American Diabetes Association’s (ADA) 79th Scientific Sessions at the Moscone Convention Center in San Francisco.

The study, “The Vitamin D and Type 2 Diabetes (D2d) Study – A Multicenter Randomized Controlled Trial for Diabetes Prevention,” included 2,423 adults aged ≥ 30 years with a body mass index between 25 kg/m² (23 kg/m² for Asian Americans) and 42 kg/m² at high risk for diabetes (defined as meeting two of the following prediabetes criteria: fasting glucose 100– 125 mg/dL [5.6–6.9 mmol/L], 2-h post load glucose after 75-g glucose load 140–199 mg/dL [7.8–11.0 mmol/L], and hemoglobin A1c 5.7–6.4% [39–47 mmol/mol]). Patients were randomized to take a daily dose of either 4,000 IU of vitamin D₃ (n = 1,211) or a matching placebo (n = 1,212). During a median 2.5 years of follow-up, patients underwent blood tests every six months to test for diabetes.

Overall, 24.2% of patients in the vitamin D group developed diabetes, compared to 26.7% in the placebo group—a difference the researchers concluded was not statistically significant.

“Even though many previous studies had observed that people with low vitamin D levels have an increased risk of type 2 diabetes, it was not known whether taking steps to increase people’s vitamin D levels would actually reduce their risk of diabetes. Our study results did not show a statistically significant benefit for vitamin D in decreasing progression to type 2 diabetes,” said principal investigator Anastassios G. Pittas, MD, MS, endocrinologist and codirector of the Diabetes and Lipid Center at Tufts Medical Center, in a meeting press release. “The results of our research underscore the need for clinical trials to confirm hypotheses raised in observational studies, and this is an important step in developing additional public and clinical recommendations.”