Can vitamin D prevent diabetes? Study seeks to find out

The National Institutes of Health (NIH) is sponsoring the first nationwide clinical trial to find out if vitamin D supplements can help delay or even prevent type 2 diabetes in people at high risk for the disease.

Researchers said they hope the Vitamin D and Type 2 Diabetes study—dubbed D2d—will come down decisively one way or another on a topic that’s been widely debated.

“This study aims to definitively answer the question: Can vitamin D reduce the risk of developing type 2 diabetes?” said Myrlene Staten, MD, the D2d project officer at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), a branch of the NIH.

“Vitamin D use has risen sharply in the U.S. in the last 15 years, since it has been suggested as a remedy for a variety of conditions, including prevention of type 2 diabetes,” Dr. Staten said. “But we need rigorous testing…That’s what D2d will do.”

The study seeks to enroll about 2,500 people over the age of 30 who have prediabetes. That means their blood glucose levels are higher than normal, but not high enough to be called diabetes.

Researchers will split the people into two groups. One group will receive a daily vitamin D supplement—specifically, vitamin D3. The other group will receive a placebo.

The study will be double-blind: Neither staff nor participants will know who is getting vitamin D or a placebo. Researchers will follow both groups for about four years.

Previous observational studies have suggested a link between vitamin D and diabetes, noted Anastassios G. Pittas, MD, D2d’s lead investigator. This and other claims about the vitamin’s benefits helped push sales of vitamin D supplements to $425 million annually, according to background information about the study.

“While there is a lot of hype about vitamin D and its health benefits, there is not yet any conclusive evidence from long-term clinical trials to support a recommendation of vitamin D supplementation for diabetes prevention,” Dr. Pittas said.

That’s also the position of The Endocrine Society. That group’s most recent statement on the issue is that “strong evidence does not exist to support the tenet that vitamin D supplementation reduces the risk of type 2 diabetes.”

According to the American Diabetes Association (ADA), nearly 26 million people in this country have diabetes. The vast majority have type 2. Although genetics plays a role in who gets type 2 diabetes, so do other factors—like excess body weight, according to the ADA.

“It is critically important to find new methods that are safe, effective and easy to use to stem the tide of future diabetes cases,” said Dr. Pittas. “Even though it is well-established that maintaining a healthy diet and staying physically active can lower the risk of diabetes, the number of people with the disease continues to increase.”

Twenty medical centers in 17 states will take part in the D2d study. Anyone who is interested in learning more or enrolling in the study should visit

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