Research synthesisLow evidenceSmall effect4 studies · 1 beneficial · 3 neutral · 0 harmful
Across 4 studies, 1 reported a beneficial small-sized effect of vitamin D supplementation on reducing fasting blood glucose (FBG), while 3 found neutral effects. The single beneficial study was a meta-analysis in patients with metabolic-associated fatty liver disease (MAFLD) reporting a small significant reduction in FBG (weighted mean difference: -0.21, 95% CI: -0.41 to -0.02). Overall, the predominant effect size is small, and effects were observed at a median duration of 84 days (12 weeks), though most studies did not report a specific dose form or range. No single dose form was used consistently across studies.
- Studied populations: obese/overweight children and adolescents; patients with metabolic-associated fatty liver disease (MAFLD); adult patients with type 2 diabetes and low vitamin D levels
Caveats: Many of the included studies did not reach statistical significance — effect may be smaller than the predominant direction suggests. Evidence base is small (only 4 studies) — conclusions should be considered preliminary. The beneficial finding came from a single meta-analysis in a specific clinical population (MAFLD), which may not generalize to healthy individuals or those with normal vitamin D levels. Doses and forms varied across studies, limiting dose-response conclusions.
Generated May 25, 2026