Vitamin D Reduces Risk of Diabetes

Researchers from Tufts University in the United States have reached a striking finding that could reshape the landscape of diabetes prevention. Their study, published in JAMA Network Open, revealed that high doses of vitamin D3 can reduce the risk of type 2 diabetes by 19 percent—but only among individuals who carry specific genetic mutations in the vitamin D receptor.

These results stemmed from a genetic analysis of data from 2,098 participants in the large-scale D2d clinical trial, a randomized, multicenter study led by Tufts University researchers. The trial examined the effects of a daily dose of 4,000 international units of vitamin D3 compared with a placebo over an average period of 2.5 years. Participants were American adults with prediabetes, a stage of elevated blood sugar that precedes a full diabetes diagnosis, a group that includes more than 115 million Americans.

The analysis focused on three common mutations in the vitamin D receptor gene, most notably the ApaI variant. It was found that individuals with the AA genotype—accounting for approximately 30 percent of the group—derived no benefit from the supplement. In contrast, those with the AC or CC genotypes, who made up the remaining 70 percent, showed a clear and measurable response, with a 19 percent reduction in diabetes risk compared with the placebo group.

Lead researcher Bess Dawson-Hughes explained that the biological basis for this differential effect lies in the presence of vitamin D receptors in pancreatic beta cells, which are responsible for insulin secretion and blood sugar regulation. Previous evidence had linked higher blood levels of vitamin D to a lower incidence of diabetes, but this new study provides, for the first time, a specific genetic explanation for the longstanding question: Why do not everyone respond to the same extent?