A new study suggests that vitamin D supplementation may help lower the risk of developing type 2 diabetes in some people with prediabetes. But the benefit appears to depend on genetics, and the findings do not apply to everyone.
The research is based on a secondary analysis of a large randomized controlled trial that originally found no significant reduction in diabetes risk from vitamin D supplementation overall. In this new analysis, researchers looked at whether differences in the vitamin D receptor gene could explain why some participants appeared to benefit while others did not.
The study, published in JAMA Network Open, analyzed more than 2,000 adults with prediabetes who were part of the D2d trial. Participants were randomly assigned to receive either 4,000 IU of vitamin D per day or a placebo and were followed to see who developed diabetes.
Researchers found that participants with certain genetic variations in the vitamin D receptor experienced a 19% lower risk of developing diabetes when taking vitamin D compared with placebo. About 30% of participants with one specific variation did not appear to benefit at all.
“But the D2d results raised an important question: Could vitamin D still benefit some people?” said Bess Dawson-Hughes, a senior scientist at Tufts University and the study’s lead author.
That question reflects a broader shift in nutrition research toward understanding why the same intervention may work differently from one person to another.
Vitamin D plays a role in how the body regulates calcium, but it is also involved in processes related to insulin function. The vitamin works by binding to a receptor found in many tissues, including the pancreas. Researchers have been exploring whether this pathway could influence how the body controls blood sugar.
In this study, genetic differences in that receptor appeared to influence how participants responded to supplementation. Those differences may help explain why earlier research on vitamin D and diabetes prevention has produced mixed results.
But the findings come with important limitations. This was a secondary analysis, meaning the genetic question was not the primary focus of the original trial. While the results are based on randomized trial data, the subgroup findings are more exploratory and need to be confirmed in future studies.
The dose used in the trial was also higher than standard recommendations. Current guidelines suggest 600 IU per day for most adults and 800 IU for older adults. Higher doses are sometimes used in clinical settings, but taking too much vitamin D can carry risks, including increased likelihood of falls and fractures.
“The findings may represent an important step toward developing a personalized approach to lowering the risk of developing type 2 diabetes among high-risk adults,” said Anastassios Pittas, a professor of medicine at Tufts University and the study’s senior author.
For now, the results do not change general guidance around vitamin D supplementation. Instead, they point to a more nuanced reality. A supplement that shows little benefit across a large group may still help specific individuals, but identifying those individuals is not yet part of routine care.
The study was supported by the U.S. Department of Agriculture and the National Institutes of Health. One author reported receiving travel expenses to a vitamin D conference from Abiogen outside the submitted work.