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Iron

What does the research say about Iron?

4 health outcomes synthesised

Iron supplementation has been researched across four health outcomes, primarily related to iron status and blood health. The strongest evidence, classified as high certainty, comes from 6 studies showing a small beneficial effect on increasing hemoglobin levels in iron-deficient or at-risk populations. Doses varied widely across studies, with most evidence from populations such as blood donors, non-anaemic iron-deficient women, and celiac patients.

Strongest evidence: The highest certainty is for Increased Hemoglobin Levels (6 studies, 5 beneficial, small effect size, high evidence strength). Moderate evidence supports Improved Iron Levels (5 studies, 4 beneficial moderate effect, one harmful in vitiligo), Reduced Iron Deficiency (5 studies, all beneficial but effect sizes mixed, moderate evidence strength with low certainty due to risk of bias), and Increased Ferritin Level (4 studies, 3 beneficial moderate effect, moderate evidence).

Mixed or weaker evidence: The iron deficiency outcome shows a uniformly positive direction, raising concerns about publication bias. Meta-analyses rated the evidence as low-certainty due to risk of bias and imprecision. For improved iron levels, one study in vitiligo patients found a harmful moderate-sized effect, indicating potential harm in that specific population. The ferritin outcome had one neutral study (iron plus probiotic vs iron alone). No outcomes had very low evidence strength, but caveats are substantial.

Effective dose patterns: Across outcomes, the most studied dose range for elemental iron is 7–105 mg/day (from one meta-analysis for improved iron levels). For reducing iron deficiency, doses ranged from 4.2 mg/day to 55 mg/day. For hemoglobin and ferritin, doses varied widely and were inconsistently reported. Study durations were typically 6–8 weeks (median 44–58 days).

Population insights: The research predominantly studied iron-deficient or at-risk populations: blood donors, non-anaemic iron-deficient women, pregnant women, and individuals with celiac disease. Female athletes were included in the ferritin study. One study in vitiligo patients showed harm, highlighting that benefits may not extend to all populations. The neutral study on hemoglobin involved rice fortification with multiple micronutrients, which may not reflect direct iron supplementation.

Notable caveats: Many meta-analyses rated the evidence as low to very low certainty. Publication bias is a concern, especially for the iron deficiency outcome where all five studies were positive. Doses and forms (elemental iron vs. other) were inconsistently reported; only one study specified the form. The evidence base is limited by small sample sizes, variable study designs, and lack of long-term data.

Frequently asked

  • What is Iron good for according to research?
    Iron supplementation has been studied for four outcomes: increasing hemoglobin levels (high evidence from 6 studies), improving iron levels (moderate evidence from 5 studies), reducing iron deficiency (moderate evidence from 5 studies), and increasing ferritin levels (moderate evidence from 4 studies). The strongest support is for raising hemoglobin in iron-deficient populations.
  • What dose of Iron is typically used in studies?
    Doses vary widely across studies, ranging from 4.2 mg/day to 105 mg/day of elemental iron, with most studies not specifying the form. The median study duration was around 6-8 weeks. No single optimal dose has been established.
  • Who benefits most from Iron?
    Research shows benefits primarily in iron-deficient or at-risk populations, including blood donors, non-anaemic iron-deficient women, pregnant women, and patients with celiac disease. However, one study in vitiligo patients found higher serum iron associated with harm, suggesting caution in that group.
  • Are there caveats or limitations in the research on Iron?
    Yes, many meta-analyses rated the evidence as low to very low certainty due to risk of bias, imprecision, and potential publication bias (especially for the iron deficiency outcome where all five studies were positive). Doses and forms were inconsistently reported, and only one study specified the form (elemental iron).
  • Does Iron help with increasing ferritin levels?
    Evidence is moderate from 4 studies; 3 reported beneficial effects (small to moderate) on ferritin levels in non-anaemic iron-deficient women, pregnant women, and female athletes. One study found no significant difference when iron was combined with probiotics. The evidence base is small and limited.
  • Is there any evidence of harm from Iron supplementation?
    One study in vitiligo patients found that higher serum iron levels were associated with vitiligo, suggesting potential harm from iron excess in that population. For other outcomes, no harmful effects were reported, but the evidence is limited by low certainty and small sample sizes.

Most-studied combinations with Iron

most supplement research is combination research
Also studied with:Calcium (2), Zinc (4), Copper (2), Selenium (3), Vitamin B9 (4), Vitamin D (2)

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