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Evidence-Based Supplement Research
Evidence-Based Supplement Research
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Vitamin D and Reduced Fasting Blood Glucose Levels

Research synthesisLow evidenceSmall effect6 studies · 1 beneficial · 5 neutral · 0 harmful

Across 6 studies, 5 found neutral small-sized effects of vitamin D supplementation on fasting blood glucose (FBG), and only 1 reported a statistically significant beneficial small-sized reduction. The single beneficial meta-analysis (2026) showed a small reduction in FBG in patients with MAFLD, but the evidence overall is predominantly neutral. Most studies were meta-analyses with short to moderate durations (median 84 days in one study), and no clear dose range or form emerged consistently across the included research.

  • Studied populations: patients with MAFLD, children and adolescents with overweight/obesity, PCOS patients, and type 2 diabetes patients

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 6 studies) — conclusions should be considered preliminary. The only beneficial finding came from a single meta-analysis in a specific clinical population (MAFLD), which may not generalize.

Generated Jun 11, 2026
Doses used in studies
  • IU/day: 10,000 (median 10,000, IQR 10,000–10,000) — 1 study
Time to effect
Median: 2.8 months · IQR 2.8 months–2.8 months · Range 2.8 months–2.8 months — Reported in 1 of 6 studies
Safety in these studies
6 of 6 papers
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