Iron
Also sold as: Elemental iron · Ferrous sulfate · Ferrous fumarate · Ferrous bisglycinate
An essential mineral for oxygen transport and cellular metabolism. Supplementation treats confirmed iron deficiency; fatigue alone is not evidence that extra iron is appropriate.
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Research
- Focus: Some cognitive domains improve in deficient school-age children, but findings are heterogeneous and do not establish a focus booster for iron-replete adults.
- Energy: Iron can reduce subjective fatigue in iron-deficient adults, including some without anemia. Benefit does not generalize to people with normal stores.
REALITY CHECK // Iron is not a universal energy booster: benefits depend on deficiency and its cause. Gentle-iron marketing does not eliminate adverse effects, while larger or more frequent doses can increase hepcidin and GI burden without proportional benefit.
Levels: how we grade evidence. Grey = evidence of no benefit; amber = evidence it makes this goal worse.
Ratings are self-reported by a self-selected group of users: how it felt, not proof that it works.
Check your bottle
Compare what your label says with what was used in trials. This is a trial range, not a personal prescription.
Enter the amount from your label to see the result.
How it was studied
UPPER LIMIT // US adult and age 14+ UL: 45 mg/day elemental iron total intake, based on GI effects; younger children have lower age-specific limits. The dossier reports no formal historical EFSA UL; current European guidance needs primary-source review. Therapeutic doses may exceed a population UL only within medical care.
Summary
Oral iron increases hemoglobin and restores stores in iron deficiency anemia. Subjective fatigue can improve when stores are low, but objective performance results vary. Excess iron accumulates, and the cause of deficiency must be addressed rather than repeatedly supplementing unexplained low ferritin.
Mechanism
Iron supports hemoglobin, myoglobin and enzymes. A dose raises hepcidin, which reduces subsequent intestinal uptake; higher frequency therefore does not reliably mean faster repletion. There is no active regulated pathway for eliminating large excess stores.
Typical studied dose
The dossier describes therapeutic iron-deficiency anemia exposures of 65–200 mg/day elemental iron under supervision. Alternate-day and single-dose trials in deficient women improved fractional absorption; clinical reviews suggest comparable efficacy with possible tolerability advantages. Neither regimen is a universal prescription.
Upper limit
US adult and age 14+ UL: 45 mg/day elemental iron total intake, based on GI effects; younger children have lower age-specific limits. The dossier reports no formal historical EFSA UL; current European guidance needs primary-source review. Therapeutic doses may exceed a population UL only within medical care.
Popular stacks with Iron
Not enough stack data yet. A combination with Iron appears here once 5 people rate the same set.
Forms and label traps
| Form on label | Active content | Studied range / day | Absorption & GI tolerance | Verdict |
|---|---|---|---|---|
| Hydrated ferrous sulfate: raw salt mass Best for: Comparison with the exact ingredient and dose basis on the Supplement Facts panel. |
20% elemental / active | 65–200 mg | Explicit hydrated-salt illustration: approximately 20% elemental iron, so 325 mg provides about 65 mg. Use the bottle-declared elemental iron if salt hydration is unknown. Sulfate commonly causes constipation, nausea and discomfort. See the form-specific clinical note; tolerance depends on dose and medical context. |
Studied standard [LABEL // VERIFY_DOSE_BASIS] Explicit hydrated-salt illustration: approximately 20% elemental iron, so 325 mg provides about 65 mg. Use the bottle-declared elemental iron if salt hydration is unknown. Sulfate commonly causes constipation, nausea and discomfort. |
| Ferrous fumarate: raw salt mass Best for: Comparison with the exact ingredient and dose basis on the Supplement Facts panel. |
33% elemental / active | 65–200 mg | Approximately 33% elemental iron. Compare at matched elemental dose; smaller tablet mass does not establish better efficacy or tolerance. Already-declared iron mg must not be converted a second time. See the form-specific clinical note; tolerance depends on dose and medical context. |
Good option [LABEL // VERIFY_DOSE_BASIS] Approximately 33% elemental iron. Compare at matched elemental dose; smaller tablet mass does not establish better efficacy or tolerance. Already-declared iron mg must not be converted a second time. |
| Ferrous bisglycinate: product-dependent chelate mass Best for: Comparison with the exact ingredient and dose basis on the Supplement Facts panel. |
20% elemental / active | no comparable trial range | About 20% elemental iron is a common product specification, not universal chelate stoichiometry. Confirm the assay on the label; if not verified use declared elemental mg. Meta-analysis supports hematologic response, but no universal form-specific trial range is specified and gentle does not mean side-effect-free. See the form-specific clinical note; tolerance depends on dose and medical context. |
Good option [LABEL // VERIFY_DOSE_BASIS] About 20% elemental iron is a common product specification, not universal chelate stoichiometry. Confirm the assay on the label; if not verified use declared elemental mg. Meta-analysis supports hematologic response, but no universal form-specific trial range is specified and gentle does not mean side-effect-free. |
Common label traps
- TRAP_01 // Take iron whenever you feel tired
Iron can help when stores are deficient; replete people have no established energy benefit and can accumulate excess. - TRAP_02 // 325 mg iron salt means 325 mg elemental iron
Hydrated ferrous sulfate at about 20% provides roughly 65 mg elemental iron. Salt hydration and product assay matter. - TRAP_03 // More and more often replenishes stores faster
Hepcidin reduces later absorption; single/alternate-day schedules have an absorption rationale, but the clinical regimen needs individual assessment. - TRAP_04 // Gentle iron never causes GI symptoms
Bisglycinate may be useful when standard salts are poorly tolerated, but adverse effects remain possible and product claims exceed comparative data.
Other outcomes studied
Outside the five leaderboard goals. Same evidence levels as above.
- IRON DEFICIENCY ANEMIA Strong · benefit
Oral iron improves hemoglobin and ferritin; a 129-RCT pediatric meta-analysis supports correction. This requires diagnosis and does not authorize empiric high doses for fatigue.
PMID 36849195 PMID 39951396 PMID 26561626 - FATIGUE VS PERFORMANCE Limited · benefit
In non-anemic deficient adults, subjective fatigue can improve while objective physical capacity effects are inconsistent. No established performance benefit in replete athletes.
PMID 29626044 PMID 39536912 PMID 30909645 - RESTLESS LEGS Moderate · benefit
Systematic reviews support reduced symptom severity in selected patients; populations, formulations and routes vary, so not all evidence is oral-only. Ferritin thresholds and treatment belong to the clinician.
PMID 30798983 PMID 30609006 - PREGNANCY Moderate · benefit
Reviews show reduced maternal anemia and deficiency; evidence for important newborn outcomes remains insufficient. Dose and indication require obstetric oversight.
PMID 39145520 PMID 39163033 - CHILD COGNITION / ADHD Limited · benefit
Selected cognitive-domain improvements depend on baseline status. ADHD and other neurodevelopmental evidence remains sparse and heterogeneous; not a first-line ADHD treatment.
PMID 37368919 PMID 38343311 PMID 34836314 - HAIR LOSS Limited · benefit
Low iron is associated with some female hair-loss presentations; supplementation has not established hair regrowth in strong RCT evidence.
PMID 16635664 PMID 40627570 - ALTERNATE-DAY ABSORPTION Moderate · benefit
Absorption trials in deficient women show hepcidin-mediated benefits from spacing doses; clinical reviews find broadly comparable response with potential tolerability advantages. Fractional uptake does not alone settle the best regimen.
PMID 26289639 PMID 29032957 PMID 31413088 PMID 37979057 - GI EFFECTS / REPLETION WITHOUT DEFICIENCY Moderate · makes it worse
Sulfate increases GI adverse effects. Routine iron in replete children has context-specific harm signals, including infection-endemic settings; unnecessary exposure should not be generalized as safe.
PMID 25700159 PMID 17158406
Reader questions
Which dose is safe and effective for me?
Diagnosis, ferritin, blood count, inflammation, ongoing losses and formulation matter. The adult population UL is 45 mg elemental/day; higher therapeutic trial doses are medical treatment, not a general target.
Which form is easiest on the stomach?
Sulfate has strong efficacy evidence but frequent GI effects. Bisglycinate is an option for intolerance, with no guarantee of zero symptoms. Compare elemental dose rather than capsule mass.
Why did I feel worse after starting iron?
Constipation, nausea and abdominal discomfort are common, but severe symptoms or suspected overdose need urgent assessment. Do not automatically increase the dose or assume worsening fatigue confirms deficiency.
How long does ferritin take to recover?
Hemoglobin can respond over weeks while stores often take months. Repeated decline requires evaluation of ongoing blood loss, inadequate intake or malabsorption rather than indefinite self-treatment.
Stack interactions
- Caution Levothyroxine [CAUTION // CLINICAL_REVIEW]
Iron forms complexes and reduces absorption. The dossier recommends at least four hours separation; confirm the exact drug instructions and reassess thyroid status when iron starts or stops. - Caution Tetracyclines and fluoroquinolones [CAUTION // CLINICAL_REVIEW]
Chelation reduces absorption. The dossier suggests a 2–4 hour separation, but precise spacing depends on the antibiotic and must follow its label. - Caution Acid suppression, coffee/tea, calcium and zinc [CAUTION // CLINICAL_REVIEW]
PPIs/H2 blockers can reduce non-heme uptake; tannins, calcium and high zinc intake can also interfere. This dossier provides pharmacological precautions without drug-specific PMID support. - Caution Vitamin C [CAUTION // CLINICAL_REVIEW]
Enhances non-heme absorption mechanistically, but should not be treated as a required high-dose add-on. The iron dossier lacks direct comparative citation for routine vitamin C coadministration. - Caution Curcumin and copper balance [CAUTION // CLINICAL_REVIEW]
Curcumin-related iron binding is an incompletely established concern; chronic excess iron can disturb copper balance. Do not infer a treatment protocol from forum reports.
Red flags: interactions and who should avoid it
Interactions
Levothyroxine: Iron forms complexes and reduces absorption. The dossier recommends at least four hours separation; confirm the exact drug instructions and reassess thyroid status when iron starts or stops. Tetracyclines and fluoroquinolones: Chelation reduces absorption. The dossier suggests a 2–4 hour separation, but precise spacing depends on the antibiotic and must follow its label. Acid suppression, coffee/tea, calcium and zinc: PPIs/H2 blockers can reduce non-heme uptake; tannins, calcium and high zinc intake can also interfere. This dossier provides pharmacological precautions without drug-specific PMID support. Vitamin C: Enhances non-heme absorption mechanistically, but should not be treated as a required high-dose add-on. The iron dossier lacks direct comparative citation for routine vitamin C coadministration. Curcumin and copper balance: Curcumin-related iron binding is an incompletely established concern; chronic excess iron can disturb copper balance. Do not infer a treatment protocol from forum reports.
Avoid or ask a doctor first if
Do not supplement with hemochromatosis, iron overload or anemia not shown to be iron-deficient. Liver disease, inflammation, pregnancy and childhood require individualized care. Accidental child ingestion can be fatal: secure storage and urgent poison assessment for suspected overdose. Severe vomiting, abdominal pain, bleeding or collapse after ingestion is an emergency.
Sources (PubMed, 12)
- Oral iron supplementation and anaemia in children according to schedule, duration, dose and cosupplementation: a systematic review and meta-analysis of 129 randomised trials.
PMID 36849195 · 2023 · Systematic review / meta-analysisPediatric meta-analysis of 129 randomized trials supporting hematologic correction.
- Efficacy of iron supplementation on fatigue and physical capacity in non-anaemic iron-deficient adults: a systematic review of randomised controlled trials.
PMID 29626044 · 2018 · Systematic review / meta-analysisNon-anemic iron-deficient adults: fatigue versus objective capacity outcomes.
- Iron for the treatment of restless legs syndrome.
PMID 30609006 · 2019 · Systematic review / meta-analysisRestless legs review; route and population caveats matter.
- Effects of iron supplementation on cognitive development in school-age children: Systematic review and meta-analysis.
PMID 37368919 · 2023 · Systematic review / meta-analysisSchool-age cognitive outcomes vary with baseline iron status.
- Daily oral iron supplementation during pregnancy.
PMID 39145520 · 2024 · Systematic review / meta-analysisMaternal anemia and deficiency outcomes with oral pregnancy supplementation.
- 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.
PMID 39163033 · 2024 · Systematic review / meta-analysisEvidence review separates hematologic effects from uncertain clinical newborn outcomes.
- Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women.
PMID 26289639 · 2015 · Randomized controlled trialHepcidin response and reduced subsequent fractional iron absorption.
- 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.
PMID 29032957 · 2017 · Randomized controlled trialOpen-label randomized absorption studies comparing schedules.
- Daily versus alternate day oral iron therapy in iron deficiency anemia: a systematic review.
PMID 37979057 · 2024 · Systematic review / meta-analysisDaily versus alternate-day clinical therapy review.
- Ferrous sulfate supplementation causes significant gastrointestinal side-effects in adults: a systematic review and meta-analysis.
PMID 25700159 · 2015 · Systematic review / meta-analysisSulfate gastrointestinal adverse-effect meta-analysis.
- 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.
PMID 36728680 · 2023 · Systematic review / meta-analysisBisglycinate effects on hemoglobin/ferritin, not proof of universal tolerability superiority.
- Iron supplementation in early childhood: health benefits and risks.
PMID 17158406 · 2006 · Systematic review / meta-analysisEarly-childhood benefits and context-dependent supplementation risks.
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