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Evidence-Based Supplement Research
Evidence-Based Supplement Research
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Vitamin D and Increased Hemoglobin Levels

Research synthesisLow evidenceModerate effect3 studies · 2 beneficial · 1 neutral · 0 harmful

Across 3 studies, 2 reported beneficial effects of vitamin D supplementation on hemoglobin levels, with effect sizes ranging from small to moderate. The beneficial findings were statistically significant and primarily observed in clinical populations (children with inflammatory bowel disease and adults with extrapulmonary tuberculosis), with the median study duration of approximately 9 months (273 days). The evidence is mixed, with one neutral study in a pediatric clinical population, suggesting the effect may depend on baseline health status.

  • Studied populations: clinical populations (children with inflammatory bowel disease and vitamin D deficiency; adults with extrapulmonary tuberculosis)

Caveats: Evidence base is small (only 3 studies) — conclusions should be considered preliminary. The neutral study in children with inflammatory bowel disease suggests the effect may not be uniform across all populations, and doses varied widely (from 2000 IU daily to high single doses of 400,000–800,000 IU), making it difficult to identify an optimal dose range.

Generated Jun 11, 2026
Doses used in studies
  • IU single-dose: 2,000–800,000 (median 401,000, IQR 2,000–800,000) — 1 study
  • IU/day: 1,000 (median 1,000, IQR 1,000–1,000) — 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 3 studies
3 of 3 papers
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