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Evidence-Based Supplement Research
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Vitamin D and Increased 25-hydroxyvitamin D Level

Research synthesisHigh evidenceModerate effect5 studies · 5 beneficial · 0 neutral · 0 harmful

Across all 5 studies, 5 reported beneficial effects on increased 25-hydroxyvitamin D levels, all statistically significant. The predominant effect size is moderate, with one study reporting a large effect. The median study duration was 90 days, indicating effects are typically observed at 8-12 weeks. The most-studied populations include older adults, healthy children, and clinical populations (Parkinson's disease, lupus, multiple sclerosis).

  • Effective dose range: 1000-7000 IU/day (weekly dosing up to 100,000 IU used in one high-dose study)
  • Studied populations: older adults, healthy children aged 10-14 years, Parkinson's disease patients with vitamin D deficiency, systemic lupus erythematosus inpatients, multiple sclerosis patients

Caveats: Available evidence is overwhelmingly positive — clinical literature in this area is subject to publication bias (null-result studies are less likely to be published or indexed). Only one study specified the form (vitamin D3); the meta-analysis compared calcifediol to cholecalciferol, noting calcifediol may be more efficacious. Doses varied widely across studies, and most studies had small sample sizes (15-35 participants in the clinical trials).

Generated May 12, 2026
Doses used in studies
  • D3 · IU/week: 17,000 (median 17,000, IQR 17,000–17,000) — 1 study
  • IU/day: 240 (median 240, IQR 240–240) — 1 study
  • IU/week: 50,000 (median 50,000, IQR 50,000–50,000) — 1 study
Time to effect
Median: 3 months · IQR 11.6 weeks–3.7 months · Range 8 weeks–5.6 months — Reported in 4 of 5 studies
5 of 5 papers
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