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

Research synthesisHigh evidenceMixed effect size16 studies · 14 beneficial · 2 neutral · 0 harmful

Across 16 studies, 14 reported beneficial effects of vitamin D supplementation on increasing 25-hydroxyvitamin D levels, with 14 statistically significant findings. Effect sizes varied from small to large (predominantly mixed), and effects were typically observed at 8–12 weeks (median study duration 90 days). Doses ranged widely (240–4000 IU/day and weekly boluses up to 50,000 IU), with no single dominant dose or form.

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). Two studies found neutral effects (in phenylketonuria patients and kidney transplant recipients), suggesting that in certain populations the effect may be absent or blunted. Most studies did not specify the form of vitamin D; where specified, vitamin D3 (cholecalciferol) was used. Most trials lasted ≥8 weeks, so shorter durations may not produce the observed effect.

Generated Jul 12, 2026
Doses used in studies
  • IU/day: 240–4,000 (median 4,000, IQR 1,000–4,000) — 5 studies
  • D3 · IU/day: 100,000 (median 100,000, IQR 100,000–100,000) — 1 study
  • IU single-dose: 25,000 (median 25,000, IQR 25,000–25,000) — 1 study
  • IU/week: 50,000 (median 50,000, IQR 50,000–50,000) — 1 study
Time to effect
Median: 3 months · IQR 2.9 months–3 months · Range 8 weeks–5.6 months — Reported in 10 of 16 studies
Safety in these studies
16 of 16 papers
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