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Evidence-Based Supplement Research
Evidence-Based Supplement Research
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Vitamin D and Reduced Vitamin D Deficiency

Research synthesisLow evidenceModerate effect4 studies · 2 beneficial · 2 neutral · 0 harmful

Across 4 studies, 2 reported beneficial effects (1 moderate, 1 large) and 2 reported neutral small effects on reducing vitamin D deficiency. The evidence suggests benefit in deficient clinical populations, with a daily dose of 2000 IU showing moderate effects over 12 months. Median study duration was 273 days, indicating effects typically observed over extended periods.

  • Effective dose range: 2000 IU daily
  • Studied populations: children with inflammatory bowel disease and vitamin D deficiency, pregnant women in low- and middle-income countries

Caveats: Evidence base is small (only 4 studies) — conclusions should be considered preliminary. Many of the included studies did not reach statistical significance — effect may be smaller than the predominant direction suggests. The two beneficial studies focused on deficient or clinical populations; results may not generalize to healthy individuals with adequate vitamin D levels.

Generated Jul 15, 2026
Doses used in studies
  • IU single-dose: 2,000–800,000 (median 401,000, IQR 2,000–800,000) — 1 study
Time to effect
Median: 9.1 months · IQR 7.5 months–10.6 months · Range 6 months–12.2 months — Reported in 2 of 4 studies
Safety in these studies
4 of 4 papers
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