Vitamin D May Help Some People With Prediabetes

A new study from Tufts University suggests that vitamin D may help delay or prevent diabetes in some adults with prediabetes, but the benefit appears to depend on genetic variation. Published in JAMA Network Open, the analysis found that people with certain variants of the vitamin D receptor gene had a 19% lower risk of developing diabetes when they took a high daily dose of vitamin D.

The study builds on data from the D2d trial, a large multicenter study that tested whether 4,000 units of vitamin D per day could reduce diabetes risk in more than 2,000 U.S. adults with prediabetes. The original trial did not find a significant overall benefit. That result led the researchers to ask whether vitamin D might still help certain subgroups rather than the full study population.

To explore that question, the team analyzed genetic data from 2,098 participants who had agreed to DNA testing. They grouped participants by response to vitamin D supplementation and then examined three common variants in the vitamin D receptor gene. The analysis showed that adults with the AA variation of the ApaI vitamin D receptor gene, which made up about 30% of the study group, did not benefit from vitamin D compared with placebo. In contrast, people with the AC or CC variations had a significantly lower risk of developing diabetes when given vitamin D.

The researchers noted that this may help explain why earlier analyses found that higher blood levels of 25-hydroxyvitamin D were linked to lower diabetes risk. Because vitamin D works by binding to the vitamin D receptor, the gene’s variation may affect how strongly a person responds to supplementation. The pancreas also contains vitamin D receptors, suggesting a possible role in insulin release and blood sugar control. 

The authors emphasized that these findings do not mean people should start taking high doses of vitamin D on their own. Current guidelines recommend 600 IU per day for adults ages 1 to 70 and 800 IU for those older than 70. Too much vitamin D can be harmful, and more research is needed to identify who might benefit from higher doses.

Still, the study points toward a possible personalized approach to diabetes prevention. The authors suggest that a relatively simple genetic test could eventually help identify adults with prediabetes who are most likely to benefit from vitamin D supplementation.