D2d — No Defense against Diabetes

This editorial critiques the findings of the D2d trial, which investigated whether high dose vitamin D supplementation (4000 IU/day) could prevent type 2 diabetes in 2423 adults with prediabetes. Despite preclinical and observational data suggesting a link between vitamin D deficiency and impaired glucose metabolism, the trial found no significant reduction in diabetes incidence over 2.5 years (hazard ratio: 0.88; 95% CI: 0.75–1.04; P=0.12). Subgroup analyses revealed a potential benefit only in severely deficient participants (<12 ng/mL; HR: 0.38), but the study was underpowered for this group. The results contrast with stronger effects seen in lifestyle or metformin interventions. The author concludes that vitamin D’s role in diabetes prevention, if any, is modest and likely limited to deficient populations, highlighting the need for targeted research in high-risk groups.

This editorial critiques the findings of the D2d trial, which investigated whether high dose vitamin D supplementation (4000 IU/day) could prevent type 2 diabetes in 2423 adults with prediabetes. Despite preclinical and observational data suggesting a link between vitamin D deficiency and impaired glucose metabolism, the trial found no significant reduction in diabetes incidence over 2.5 years (hazard ratio: 0.88; 95% CI: 0.75–1.04; P=0.12). Subgroup analyses revealed a potential benefit only in severely deficient participants (<12 ng/mL; HR: 0.38), but the study was underpowered for this group. The results contrast with stronger effects seen in lifestyle or metformin interventions. The author concludes that vitamin D’s role in diabetes prevention, if any, is modest and likely limited to deficient populations, highlighting the need for targeted research in high-risk groups.