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Iron

What does the research say about Iron?

4 health outcomes synthesised

Iron supplementation has been studied across 4 health outcomes, with the strongest evidence supporting its role in increasing hemoglobin levels and reducing iron deficiency. Research includes 5 studies on hemoglobin, primarily in non-anaemic iron-deficient women of reproductive age, using doses of 7–105 mg/day elemental iron. Evidence quality is moderate overall, though publication bias and small sample sizes remain limitations.

Strongest evidence: The strongest research supports iron for increasing hemoglobin levels (4 of 5 studies beneficial; moderate evidence) and reducing iron deficiency (4 of 4 studies beneficial; moderate evidence). For hemoglobin, effects were consistently small, with doses of 7–105 mg/day elemental iron used in one meta-analysis. For iron deficiency, effect sizes ranged from small to large across populations including pregnant women and general populations, with doses from 0.2–112.8 mg/day.

Mixed or weaker evidence: Low-certainty evidence suggests iron improves iron levels (3 of 4 studies beneficial, moderate effect sizes) and ferritin levels (3 of 4 studies beneficial, small to moderate effects). However, one study in vitiligo patients found a harmful association (higher serum iron), and one study in athletes with low iron stores did not reach significance (p=0.056), indicating benefits may not generalize.

Effective dose patterns: Across outcomes, effective doses commonly fall in the range of 7–105 mg/day elemental iron, though some studies used 4.2–55 mg/day or 0.2–112.8 mg/100 g food. There is no clear convergence on a single optimal dose or form, and doses varied widely between supplementation and fortification studies.

Population insights: Non-anaemic iron-deficient women of reproductive age and pregnant women are the most studied populations, showing consistent benefits. Healthy blood donors also respond well. However, one study in vitiligo patients and a neutral result in female athletes suggest that benefits may depend on baseline iron status and clinical condition.

Notable caveats: Across syntheses, publication bias is a recurring concern—null-result studies are less likely to be published. Evidence certainty is limited by small sample sizes, risk of bias, and imprecision. Many studies used multiple micronutrients, making it difficult to isolate iron's effect alone.

Frequently asked

  • What is Iron good for according to research?
    Research supports iron for increasing hemoglobin levels (4 of 5 studies beneficial, moderate evidence) and reducing iron deficiency (4 of 4 studies beneficial, moderate evidence). Lower-certainty evidence also suggests benefits for improving iron levels and ferritin levels, with 3 of 4 studies beneficial in each case.
  • What dose of Iron is typically used in studies?
    Doses vary widely across studies. For hemoglobin and iron levels, a common range is 7–105 mg/day elemental iron. For ferritin, studies used 4.2–55 mg/day. Fortification studies reported doses of 0.2–112.8 mg/100 g food. No single dose emerged as clearly optimal.
  • Who benefits most from Iron?
    Non-anaemic iron-deficient women of reproductive age and pregnant women are the most studied and show consistent benefits. Healthy blood donors also respond well. However, benefits may not generalize to all populations—one study in vitiligo patients found a harmful association, and athletes with low iron stores showed non-significant results.
  • Are there caveats or limitations in the research on Iron?
    Yes. Across all syntheses, publication bias is a concern—null-result studies are less likely to be published. Evidence certainty is often low or moderate due to small sample sizes, risk of bias, and imprecision. Many studies used multiple micronutrients, making it hard to isolate iron's effect alone.
  • Does Iron help with iron deficiency?
    Yes. All 4 studies on reducing iron deficiency reported beneficial effects, with moderate evidence strength. Effect sizes ranged from small to large (e.g., RR 0.24 for maternal deficiency at term; RR 0.36 with food fortification). Pregnant women and general populations showed the strongest responses.
  • How long do studies on Iron typically last?
    Study durations vary but are often short. For hemoglobin, the median study duration was 58 days. For ferritin, benefits were typically observed over 28–60 days. No long-term safety or efficacy data are well-documented in these syntheses.

Most-studied combinations with Iron

most supplement research is combination research
Also studied with:Calcium (2), Zinc (3), Selenium (3), Vitamin B9 (3)

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