Genetic Testing May Unlock Vitamin D's Potential for Diabetes Prevention

Not all patients with prediabetes may benefit equally from vitamin D supplementation to reduce their risk of developing type 2 diabetes, but a common genetic test could reveal who will.¹

A study published in JAMA Network Open found that the benefit of high-dose vitamin D₃ appears to be restricted to adults carrying specific variants of the vitamin D receptor (VDR) gene, opening a potential pathway toward more personalized diabetes prevention.

“Improving vitamin D status may reduce diabetes risk, particularly among individuals with prediabetes who are at high risk of progression to type 2 diabetes,” wrote the researchers of the study. “To test this hypothesis, 3 vitamin D and diabetes prevention randomized clinical trials have been conducted, enrolling participants with prediabetes and using progression to diabetes or regression to normoglycemia as key outcomes.”

The analysis drew on data from a multisite, randomized, double-blind, placebo-controlled trial that enrolled more than 2000 adults with prediabetes between 2013 and 2018. Participants received either 4000 IU per day of vitamin D₃ or placebo and were followed for a median (IQR) of 2.5 (1.8-3.5) years for incident diabetes.

Three common polymorphisms of the VDR gene—ApaI, BsmI, and FokI—were examined among 2098 D2d participants with available genotyping data. Researchers first conducted a discovery analysis to determine whether VDR variants were associated with diabetes risk across different achieved vitamin D levels, then applied those findings to a test-phase analysis comparing outcomes between treatment and placebo groups stratified by genotype.

A Responder and Nonresponder Split

Among the 618 participants carrying the ApaI AA genotype—representing about 30% of the cohort—vitamin D₃ treatment produced no meaningful reduction in diabetes risk (HR, 1.02; 95% CI, 0.72-1.44). In contrast, the 1480 participants with ApaI AC or CC genotypes showed a 19% decrease in the risk of developing diabetes with supplementation (HR, 0.81; 95% CI, 0.66-0.99).

Additionally, the BsmI polymorphism showed near-complete overlap with the ApaI findings, in which 260 of 261 participants with the nonresponsive BsmI TT genotype also carried the nonresponsive ApaI AA genotype, suggesting that a single ApaI genotype test is sufficient to identify likely responders and nonresponders.

Why Genetics May Explain Inconsistent Trial Results

The VDR is expressed in pancreatic β cells, where it influences insulin secretion and glucose metabolism, providing a plausible biological mechanism for the gene–supplement interaction observed. Prior research in the UK Biobank had suggested that the BsmI T allele was associated with greater diabetes risk reduction at higher vitamin D levels among adults with prediabetes, lending additional plausibility to the genotype-modified effect seen here.

However, the researchers acknowledged some limitations. First, the study's findings are exploratory and require replication in an independent clinical trial before clinical implementation can be considered. Additionally, the analysis was limited to 3 VDR polymorphisms and did not account for other genetic variants that may influence vitamin D metabolism or diabetes risk, and the Medicare-based cohort was restricted to adults over age 65, precluding generalizability to younger patients with prediabetes.

Despite these limitations, the researchers believe these findings suggest that ApaI genotyping could represent one of the first actionable pharmacogenomic tools in diabetes prevention.

The scale of the at-risk population underscores why these findings matter. More than 115 million American adults, or more than 2 in 5, have prediabetes, and 8 in 10 of them do not know they have it.² According to the CDC's 2026 National Diabetes Statistics Report, over 40 million Americans are currently living with diabetes, with an estimated 11 million cases undiagnosed, and approximately 1.5 million new diagnoses are made every year. The economic burden is equally staggering, with the total estimated cost of diagnosed diabetes in the US reaching $412.9 billion in 2022, including $306.6 billion in direct medical costs.

Therefore, a targeted, inexpensive intervention like genotype-guided vitamin D supplementation could represent a meaningful and scalable tool in the effort to slow the diabetes epidemic.

“This genetic association study of adults with prediabetes suggests that diabetes risk reduction after supplementation with 4000 IU/d of vitamin D₃ was restricted to participants carrying the AC and CC alleles of the ApaI polymorphism,” wrote the researchers.¹ “These findings support the potential role of ApaI genotyping in identifying individuals most likely to experience benefits from high-dose vitamin D₃ treatment to reduce diabetes risk.”

References

1. Dawson-Hughes B, Huggins GS, Nelson J, et al. Vitamin D receptor polymorphisms and the effect of vitamin D supplementation on diabetes risk among adults with prediabetes. JAMA Netw Open. 2026;9(4):e267332. doi:10.1001/jamanetworkopen.2026.7332

2. CDC. National diabetes statistics report. January 21, 2026. Accessed May 6, 2026. https://www.cdc.gov/diabetes/php/data-research/index.html