Iron
Mixed EvidenceCritical for oxygen transport — but only supplement if deficient.
Not medical advice
Nutripedia summarises published peer-reviewed research. This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional before taking any supplement.
Iron is essential for haemoglobin production and oxygen transport in the blood. Deficiency causes fatigue and anaemia, particularly in women, athletes, and vegetarians. However, excess iron is harmful, so supplementation should be guided by blood tests.
Essential for those with confirmed deficiency. Routine supplementation without testing is not recommended due to toxicity risks.
Evidence Database
Click any row to explore the studies behind each health outcome. Grades reflect the volume and quality of published research, not a recommendation.
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General Information
Dosage (Evidence-Reported)
These figures reflect what clinical studies used — not personalised recommendations.
Safety Notes
- Do not supplement without a confirmed deficiency via blood test
- Excess iron causes oxidative damage and organ toxicity
- Can cause constipation and GI distress
- Keep away from children — iron overdose is dangerous
Key Benefits
- Corrects iron-deficiency anaemia
- Restores energy levels in deficient individuals
- Essential for oxygen transport and athletic performance
Quick Facts
Nutripedia is an educational resource. Content is sourced from peer-reviewed studies and does not constitute medical advice. Consult a healthcare professional before starting any supplement.
The Evidence
15 peer-reviewed papers, updated yesterday
4 meta-analyses · 3 systematic reviews · 5 RCTs · 1 cohort study · 1 position stand · 1 regulatory document
Iron - Health Professional Fact Sheet
National Institutes of Health Office of Dietary Supplements
NIH Office of Dietary Supplements
Authoritative NIH reference compiling RDAs (8 mg men; 18 mg pre-menopausal women; 27 mg pregnancy), tolerable upper intake level of 45 mg/day for adults, and evidence-based risk-group identification including pregnant women, infants, menstruating women, frequent blood donors, and patients with cancer or gastrointestinal disorders.
Management of iron deficiency in children, adults, and pregnant individuals: evidence-based and expert consensus recommendations
Benson AE, Lo JO, Achebe MO et al.
Lancet Haematology
An international panel of 26 experts using GRADE methodology produced seven evidence-based recommendations and 21 expert consensus opinions covering optimal oral and intravenous iron formulations, dosing strategies, and patient selection across children, adults, and pregnant individuals, addressing the absence of prior clinical consensus in this area.
Optimal dose and duration of iron supplementation for treating iron deficiency anaemia in children and adolescents: A systematic review and meta-analysis
Rehman T, Agrawal R, Ahamed F et al.
PLoS One
Meta-analysis of 28 studies (n=8,829 children and adolescents) found a pooled haemoglobin improvement of 2.01 g/dL with iron supplementation. Low-dose iron below 5 mg/kg/day combined with treatment durations either under 3 months or over 6 months produced optimal haemoglobin outcomes. Effectiveness varied significantly by baseline haemoglobin level.
Screening and Supplementation for Iron Deficiency and Iron Deficiency Anemia During Pregnancy: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force
Cantor AG, Holmes R, Bougatsos C et al.
JAMA
Systematic review of 17 trials (n=24,023) for the USPSTF found prenatal iron supplementation reduces iron deficiency anaemia at term, but evidence for benefits on clinical outcomes such as preterm birth, low birth weight, gestational diabetes, or haemorrhage was limited or showed no statistically significant effect. No trials directly addressed screening effectiveness.
Efficacy of daily versus intermittent oral iron supplementation for prevention of anaemia among pregnant women: a systematic review and meta-analysis
Banerjee A, Athalye S, Shingade P et al.
EClinicalMedicine
Meta-analysis of 26 studies (n=4,365 pregnant women) found intermittent iron (120 mg/day) was comparable to daily iron (60 mg/day) for raising haemoglobin, but daily supplementation produced better ferritin stores. Nausea, diarrhoea, and constipation were significantly more frequent with daily dosing, making intermittent supplementation a clinically relevant lower-burden alternative.
Alternate day versus consecutive day oral iron supplementation in iron-depleted women: a randomized double-blind placebo-controlled study
von Siebenthal HK, Gessler S, Vallelian F et al.
eClinicalMedicine
In 150 iron-depleted Swiss women (ferritin ≤30 µg/L), alternate-day oral iron (100 mg on alternating days for 180 days) achieved comparable serum ferritin to daily dosing for 90 days, reduced iron deficiency at 6 months, and caused significantly fewer gastrointestinal side effects, supporting alternate-day dosing as a well-tolerated, effective regimen.
Is a Lower Dose of More Bioavailable Iron (18-mg Ferrous Bisglycinate) Noninferior to 60-mg Ferrous Sulfate in Increasing Ferritin Concentrations While Reducing Gut Inflammation and Enteropathogen Detection in Cambodian Women? A Randomized Controlled Noninferiority Trial
Fischer JAJ, Pei LX, Elango R et al.
Journal of Nutrition
In a population of predominantly iron-replete Cambodian women, 18 mg ferrous bisglycinate was inferior to 60 mg ferrous sulphate for increasing ferritin concentrations and showed no differential benefit on gut inflammation or enteropathogen detection. Findings caution against assuming bioavailability advantages of bisglycinate translate to clinical superiority at lower doses in iron-sufficient populations.
Oral iron supplementation and anaemia in children according to schedule, duration, dose and cosupplementation: a systematic review and meta-analysis of 129 randomised trials
Andersen CT, Marsden DM, Duggan CP et al.
BMJ Global Health
Meta-analysis of 129 RCTs (34,564 children) found frequent and intermittent iron supplementation schedules were similarly effective at reducing anaemia. Moderate-to-high doses outperformed low doses for improving haemoglobin and ferritin. Weekly short-duration supplementation at moderate or high doses was identified as a potentially optimal strategy for children at risk of deficiency.
The effects of oral ferrous bisglycinate supplementation on hemoglobin and ferritin concentrations in adults and children: a systematic review and meta-analysis of randomized controlled trials
Fischer JAJ, Cherian AM, Bone JN et al.
Nutrition Reviews
Meta-analysis of 17 RCTs found ferrous bisglycinate produced higher haemoglobin concentrations and fewer gastrointestinal adverse events than comparator iron forms in pregnant women. In children, pooled analyses showed no statistically significant differences in haemoglobin or ferritin versus other iron forms, indicating evidence is population-dependent.
Oral iron treatment in adult iron deficiency
Lo JO, Benson AE, Martens K et al.
European Journal of Haematology
Narrative review concluding that the hepcidin-ferroportin regulatory axis inherently limits oral iron absorption, making high-dose and frequent dosing counterproductive. Single daily or alternate-day dosing of 60–120 mg elemental iron represents a rational evidence-based approach, minimising gastrointestinal burden while exploiting natural absorption windows between doses.
Efficacy and Safety of Ferrous Bisglycinate and Folinic Acid in the Control of Iron Deficiency in Pregnant Women: A Randomized, Controlled Trial
Bumrungpert A, Pavadhgul P, Piromsawasdi T et al.
Nutrients
Ferrous bisglycinate (24 mg elemental iron) with folinic acid achieved comparable haemoglobin and ferritin increases to ferrous fumarate (66 mg elemental iron) in iron-deficient pregnant women, while producing significantly fewer reports of nausea, abdominal pain, bloating, constipation, and metallic taste, demonstrating superior tolerability at a lower elemental iron dose.
Physiologically based serum ferritin thresholds for iron deficiency in children and non-pregnant women: a US National Health and Nutrition Examination Surveys (NHANES) serial cross-sectional study
Mei Z, Addo OY, Jefferds ME et al.
Lancet Haematology
Using NHANES data (2003–2018), physiologically derived serum ferritin thresholds for iron-deficient erythropoiesis were identified as approximately 20 µg/L for children and 25 µg/L for non-pregnant women — substantially higher than WHO expert-opinion thresholds of 12 µg/L and 15 µg/L — suggesting current guidelines may underdiagnose functional iron deficiency.
Iron deficiency
Pasricha SR, Tye-Din J, Muckenthaler MU et al.
Lancet
Comprehensive seminar establishing iron deficiency as the most prevalent micronutrient deficiency worldwide. Covers pathophysiology, risk populations (pregnant women, children, menstruating women), diagnostic biomarkers (ferritin, transferrin saturation), and treatment approaches including oral and intravenous iron, noting that treatment choice depends on severity, aetiology, and patient tolerance.
Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials
Stoffel NU, Cercamondi CI, Brittenham G et al.
Lancet Haematology
In iron-depleted women, alternate-day supplementation produced 21.8% cumulative fractional iron absorption versus 16.3% with consecutive daily dosing (p=0.001), and 175 mg total iron absorbed versus 131 mg. Single morning doses outperformed split twice-daily doses. Alternate-day, single-dose iron supplementation optimises absorption by preventing hepcidin accumulation.
Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women
Moretti D, Goede JS, Zeder C et al.
Blood
In 54 iron-depleted women, oral iron doses of 60 mg or more elevated hepcidin for up to 24 hours and reduced fractional absorption by 35–45% the following day. A sixfold dose increase produced only a threefold increase in absorbed iron; twice-daily dosing showed no benefit over single daily dosing, supporting lower single doses to maximise absorption.