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Vitamin D + Type 2 Diabetes


Anastassios Pittas, MD, MS is the Co-Director of the Diabetes and Lipid Center at Tufts Medical Center in Boston.A national study lead by Tufts Medical Center researchers has found that taking vitamin D supplements does not prevent the development of type 2 diabetes in most people at high risk of the disease. But there may be some findings worth discussion, according to Anastassios G. Pittas, MD, MS, Endocrinologist and Co-Director of the Diabetes and Lipid Center at Tufts MC and Primary Investigator of the D2d study. Here are the top five take-aways of the new study, published online in the New England Journal of Medicine. 

  1. Earlier studies had suggested taking Vitamin D supplements might lower the risk of type 2 diabetes. The D2D study was the largest research project to date designed to determine if there is a link; specifically, it looked at people who were classified as “prediabetic”or at high risk for type 2 diabetes. The study involved 2,423 people with prediabetes from 22 centers across the country. Participants were given either 4,000 units of vitamin D per day or placebo and received blood tests twice per year for an average of two-and-a-half years, to monitor for the development of diabetes.

  2. Researchers found no significant benefit with the supplements. While the vitamin D group did not experience any negative effects of supplementation, including kidney stones, high blood calcium levels or reduced kidney function, vitamin D did not reduce the risk of diabetes by the target level of 25 percent or more in the total study population. 

  3. Most people in the study had sufficient vitamin D levels to start. Researchers note that 80 percent of those in the study had vitamin D levels considered sufficient by U.S. nutritional standards at the start of the study. This high percentage may have reduced D2d’s ability to detect an overall benefit of vitamin D in the total study population. 

  4. Those who had low vitamin D levels when they joined the study appeared to benefit. About four percent of the study participants had low levels of the vitamin initially, and vitamin D supplements appeared to reduce their risk of developing diabetes. However, the authors note, more research is needed to confirm this observation.

  5. People should get the right amount of vitamin D to stay healthy and make other changes to reduce diabetes risk. The D2d study’s findings do not change the need for everyone to meet the National Academy of Medicine’s daily vitamin D requirement (400-800 IU’s daily), according to the researchers. In addition, those who are at high risk for type 2 diabetes should commit to lifestyle changes—including improved diet, weight loss and increased physical activity–to lower their chances of developing the disease.