The U.S. National Institutes of Health (NIH) today announced that a new clinical trial to research vitamin D’s role in diabetes prevention has begun. The “large-scale” study, nicknamed D2d, will look at around 2,500 people over the age of 30 with prediabetes. Researchers hope to determine whether vitamin D can prevent or delay the onset of type 2 diabetes in such patients.

“This study aims to definitively answer the question: Can vitamin D reduce the risk of developing type 2 diabetes?” said Dr. Myrlene Staten, a project officer on the new study at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). “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. But we need rigorous testing to determine if vitamin D will help prevent diabetes. That’s what D2d will do.”

The study will give half of study participants a 4,000 IU dose of vitamin D daily – five times the 600 IU to 800 IU intake the NIH says adults typically receive. The other half of study participants will receive a placebo. The NIH is currently seeking participants to volunteer in the D2d study.

According to NIDDK Director Dr. Griffin Rodgers, almost 26 million Americans have diabetes (including Tom Hanks), and around 79 million more have prediabetes. Rodgers and his colleagues believe, based on previous studies, that vitamin D could reduce the risk of developing diabetes by as much as 25%.

“Past observational studies have suggested that higher levels of vitamin D may be beneficial in preventing type 2 diabetes, but until this large, randomized and controlled clinical trial is complete, we won’t know if taking vitamin D supplements lowers the risk of diabetes,” said Dr. Anastassios Pittas, principal investigator on the new study and a professor of medicine at Tufts University.