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

Research synthesisModerate evidenceModerate effect5 studies · 4 beneficial · 1 neutral · 0 harmful

Across 5 studies, 4 reported beneficial effects of vitamin D on hemoglobin levels, with effect sizes ranging from small to moderate. The predominant effect size was moderate, and effects were typically observed at a median study duration of 273 days (about 9 months). The most-studied populations were clinical groups, including children with inflammatory bowel disease, adults with tuberculosis, and patients with celiac disease, with no clear dose range converging across studies.

  • Studied populations: clinical populations (children with inflammatory bowel disease, adults with pulmonary or extrapulmonary tuberculosis, patients with celiac disease)

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 of the 5 studies lacked a specified dose or duration, limiting dose-response conclusions. The neutral study in children with inflammatory bowel disease suggests benefit may not extend to all clinical subgroups.

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
  • 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 5 studies
5 of 5 papers
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