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