{"@context":"https://schema.org","@type":"DietarySupplement","id":"https://nutripedia.co.uk/items/iron","url":"https://nutripedia.co.uk/items/iron","name":"Iron","category":"Minerals","tagline":"Critical for oxygen transport — but only supplement if deficient.","verdict":"mixed","evidenceRating":4,"verdictSummary":"Essential for those with confirmed deficiency. Routine supplementation without testing is not recommended due to toxicity risks.","dosage":{"recommended":"14–18","unit":"mg","timing":"On an empty stomach with vitamin C","notes":"Ferrous bisglycinate is better tolerated. Always test ferritin levels before supplementing."},"keyBenefits":["Corrects iron-deficiency anaemia","Restores energy levels in deficient individuals","Essential for oxygen transport and athletic performance"],"warnings":["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"],"evidenceSummary":null,"dosing":null,"safety":null,"whoMightBenefit":[],"whoShouldAvoid":[],"regulatoryNotes":null,"faqs":[{"question":"What does the research say about iron and iron deficiency anaemia?","answer":"Oral ferrous iron supplementation is the established standard-of-care treatment for iron deficiency anaemia. British Society of Gastroenterology guidelines (2011) and WHO/NHS guidance consistently recommend ferrous iron as first-line treatment. A 2015 Cochrane meta-analysis of 44 RCTs found daily iron supplementation in pregnancy reduced maternal anaemia at term by 70% and risk of low birthweight by approximately 16%. NHS guidance and iron overload trial data caution against routine supplementation without confirmed deficiency via blood test."},{"question":"What dosage ranges have been studied for iron supplementation?","answer":"In confirmed deficiency, clinical trials and BSG guidelines have studied 150–200 mg elemental iron/day in divided doses (e.g., three doses of ferrous sulfate 200 mg, providing ~65 mg elemental iron each). The NHS RNI is 8.7 mg/day (men and post-menopausal women) and 14.8 mg/day (women of reproductive age). For iron-deficient non-anaemic individuals, one RCT used 105 mg/day elemental iron for 12 weeks and demonstrated fatigue reduction. WHO recommends 30–60 mg elemental iron/day during pregnancy."},{"question":"What side effects have been reported in iron supplementation trials?","answer":"GI adverse events are the most commonly reported: constipation, nausea, epigastric discomfort, and dark stools are observed in 30–50% of participants in ferrous sulfate trials. Ferrous bisglycinate (a chelated form) and alternate-day dosing have been investigated in RCTs as strategies to reduce GI burden. At high doses, iron causes significant oxidative stress via the Fenton reaction; iron overdose is a medical emergency, particularly in children."},{"question":"Is there evidence for iron supplementation in non-anaemic but iron-deficient individuals?","answer":"Two RCTs have specifically studied iron-deficient but non-anaemic participants. A 12-week double-blind RCT (n=198, Waldvogel et al. 2012) found that iron supplementation improved fatigue scores significantly compared to placebo. A 6-week RCT (Brownlie et al. 2004) found women with tissue iron deficiency but no anaemia showed greater VO2max improvement with iron versus placebo after aerobic training. These findings suggest ferritin level — not just haemoglobin — may be a relevant threshold for supplementation decisions in clinical practice."},{"question":"Which form of iron has the strongest evidence base?","answer":"Ferrous iron salts (ferrous sulfate, ferrous fumarate, ferrous gluconate) are the most extensively studied and are NHS/BSG first-line recommendations for deficiency. Ferrous bisglycinate is a chelated form studied in RCTs for improved tolerability with comparable efficacy to ferrous sulfate. Ferric iron forms (including ferric orthophosphate) are substantially less bioavailable. Intravenous iron formulations are used in clinical settings for severe deficiency or malabsorption."},{"question":"What do NHS and SACN say about iron supplementation?","answer":"NHS guidance is explicit: 'do not take iron supplements unless advised by your GP' because too much iron can be harmful. SACN has not issued specific population-level supplementation guidance for iron in non-pregnant adults. The NHS RNI is 8.7 mg/day for adult men and post-menopausal women, and 14.8 mg/day for pre-menopausal women. Groups identified as at risk of deficiency include pregnant women, infants, vegetarians/vegans, and those with heavy menstrual periods."},{"question":"What does research say about iron supplementation and exercise performance in athletes?","answer":"In endurance athletes with documented iron deficiency (whether anaemic or non-anaemic), supplementation consistently improves markers of exercise capacity. A 2004 RCT in women with non-anaemic iron deficiency showed significantly greater VO2max gains following a 6-week aerobic training programme compared to placebo. A 2019 systematic review identified iron deficiency — even without anaemia — as a distinct risk factor for impaired aerobic adaptation. These findings relate specifically to athletes with confirmed deficiency."}],"research":{"totalCount":15,"papers":[{"title":"Iron - Health Professional Fact Sheet","year":2025,"journal":"NIH Office of Dietary Supplements","doi":null,"pmid":"","url":"https://pubmed.ncbi.nlm.nih.gov//","studyDesign":"regulatory","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Management of iron deficiency in children, adults, and pregnant individuals: evidence-based and expert consensus recommendations","year":2025,"journal":"Lancet Haematology","doi":"10.1016/S2352-3026(25)00038-9","pmid":"40306833","url":"https://doi.org/10.1016/S2352-3026(25)00038-9","studyDesign":"position-stand","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Optimal dose and duration of iron supplementation for treating iron deficiency anaemia in children and adolescents: A systematic review and meta-analysis","year":2025,"journal":"PLoS One","doi":"10.1371/journal.pone.0319068","pmid":"39951396","url":"https://doi.org/10.1371/journal.pone.0319068","studyDesign":"meta-analysis","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"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","year":2024,"journal":"JAMA","doi":"10.1001/jama.2024.13546","pmid":"39163033","url":"https://doi.org/10.1001/jama.2024.13546","studyDesign":"systematic-review","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Efficacy of daily versus intermittent oral iron supplementation for prevention of anaemia among pregnant women: a systematic review and meta-analysis","year":2024,"journal":"EClinicalMedicine","doi":"10.1016/j.eclinm.2024.102742","pmid":"39114275","url":"https://doi.org/10.1016/j.eclinm.2024.102742","studyDesign":"meta-analysis","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Alternate day versus consecutive day oral iron supplementation in iron-depleted women: a randomized double-blind placebo-controlled study","year":2023,"journal":"eClinicalMedicine","doi":"10.1016/j.eclinm.2023.102286","pmid":"38021373","url":"https://doi.org/10.1016/j.eclinm.2023.102286","studyDesign":"rct","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"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","year":2023,"journal":"Journal of Nutrition","doi":"10.1016/j.tjnut.2023.05.029","pmid":"37271416","url":"https://doi.org/10.1016/j.tjnut.2023.05.029","studyDesign":"rct","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Oral iron supplementation and anaemia in children according to schedule, duration, dose and cosupplementation: a systematic review and meta-analysis of 129 randomised trials","year":2023,"journal":"BMJ Global Health","doi":"10.1136/bmjgh-2022-010745","pmid":"36849195","url":"https://doi.org/10.1136/bmjgh-2022-010745","studyDesign":"meta-analysis","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"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","year":2023,"journal":"Nutrition Reviews","doi":"10.1093/nutrit/nuac106","pmid":"36728680","url":"https://doi.org/10.1093/nutrit/nuac106","studyDesign":"meta-analysis","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Oral iron treatment in adult iron deficiency","year":2022,"journal":"European Journal of Haematology","doi":"10.1111/ejh.13892","pmid":"36336470","url":"https://doi.org/10.1111/ejh.13892","studyDesign":"systematic-review","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Efficacy and Safety of Ferrous Bisglycinate and Folinic Acid in the Control of Iron Deficiency in Pregnant Women: A Randomized, Controlled Trial","year":2022,"journal":"Nutrients","doi":"10.3390/nu14030452","pmid":"35276810","url":"https://doi.org/10.3390/nu14030452","studyDesign":"rct","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"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","year":2021,"journal":"Lancet Haematology","doi":"10.1016/S2352-3026(21)00168-X","pmid":"34329578","url":"https://doi.org/10.1016/S2352-3026(21)00168-X","studyDesign":"cohort","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Iron deficiency","year":2021,"journal":"Lancet","doi":"10.1016/S0140-6736(20)32594-0","pmid":"33285139","url":"https://doi.org/10.1016/S0140-6736(20)32594-0","studyDesign":"systematic-review","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"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","year":2017,"journal":"Lancet Haematology","doi":"10.1016/S2352-3026(17)30182-5","pmid":"29032957","url":"https://doi.org/10.1016/S2352-3026(17)30182-5","studyDesign":"rct","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women","year":2015,"journal":"Blood","doi":"10.1182/blood-2015-05-642223","pmid":"26289639","url":"https://doi.org/10.1182/blood-2015-05-642223","studyDesign":"rct","fields":[],"conclusion":"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.","abstract":"","citationCount":0}]},"machineReadable":{"markdownUrl":"https://nutripedia.co.uk/items/iron/markdown","jsonUrl":"https://nutripedia.co.uk/items/iron/json","llmsTxt":"https://nutripedia.co.uk/llms.txt"},"disclaimer":"Informational supplement research only. Not medical advice. Consult a qualified healthcare professional before taking supplements.","lastReviewed":"2026-04-20T00:00:00.000Z","updatedAt":"2026-04-20T00:00:00.000Z"}