NutriDex

The Supplement Research Compendium
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Iron

Critical for oxygen transport — supplement only if low.

Strong evidence 🧂Mineral

✚ Updated · How we grade evidence

Evidence tier
Strong
Research weight
Citations
17 verified / 17
Classification
Mineral
❝
What the evidence says. Graded strong for treating confirmed iron-deficiency anaemia, which it reliably reverses — but the strength applies only when a blood test confirms deficiency. It is not a general energy or wellness supplement, and is harmful in iron overload. (Strong evidence: Multiple high-quality RCTs / meta-analyses with consistent effects.)
⚠
Use with care. Iron overdose is a leading cause of fatal poisoning in young children — keep tablets locked away. Taking iron without a confirmed deficiency is also harmful: in iron-overload conditions such as haemochromatosis it accelerates organ damage. Supplement only when a blood test confirms you need it.

What is Iron?

Iron is a mineral used for treats iron-deficiency anemia. NutriDex grades the human evidence as Strong. Iron is essential for hemoglobin and oxygen transport. Iron-deficiency anemia causes fatigue, poor concentration, and reduced exercise capacity, and supplementation reliably reverses it. Crucially, iron should only be supplemented when deficiency is confirmed — excess iron is pro-oxidant and dangerous, especially in conditions like hemochromatosis. Alternate-day dosing reduces side effects and may improve absorption.

Purported Benefits

✓Treats iron-deficiency anemia
✓Restores energy (if deficient)
✓Supports cognition

Evidence by outcome

The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.

OutcomeEvidenceEffectStudies
Treats/prevents iron-deficiency anemiaGuidelines and Cochrane reviews confirm oral iron reliably corrects deficiency anemia; only when deficient. Strong ↑ benefit · large 4
Cognition in childrenMeta-analysis (12 RCTs) improved intelligence/attention/memory, largest in baseline-anemic children. Moderate ↑ benefit · moderate 1
Heart failure with iron deficiency (IV iron)Meta-analyses show fewer HF hospitalizations with IV iron but no mortality benefit; IV, not oral. Moderate ↑ benefit · small 3
Restless legs syndromeMeta-analysis (12 RCTs) found reduced RLS scores, mainly with IV ferric carboxymaltose. Moderate ↑ benefit · moderate 1
Alternate-day vs daily dosingPooled RCTs show no significant hemoglobin difference; alternate-day may improve absorption/tolerability. Moderate — no effect · negligible 3

Dosing & Compounds

Typical Dose
Treatment ~40–60 mg elemental; alternate-day dosing may absorb better. Test before supplementing.
Active Compounds
Ferrous sulfateFerrous bisglycinate

Safety & Cautions

Constipation, nausea and dark stools are common. Overdose is dangerous and is a leading cause of pediatric poisoning. Excess iron is pro-oxidant and harmful in iron-overload conditions (e.g. haemochromatosis). Separate from calcium, antacids, levothyroxine and certain antibiotics (tetracyclines, fluoroquinolones), which it can bind. Never take without a confirmed need. Educational only — always check with your doctor or pharmacist before combining Iron with any medicine.

Iron drug interactions

Known or theoretical interactions between Iron and common medications — educational, not exhaustive. Always check with your doctor or pharmacist before combining Iron with any medicine.

Caution
Levothyroxine, some antibiotics, levodopa
Iron binds these drugs and reduces absorption; separate by 2–4 hours.
Iron chelates levothyroxine, fluoroquinolones, tetracyclines, bisphosphonates and levodopa. NIH ODS — Iron

Key Studies ★ 17 studies

Cochrane review Finkelstein 2024 (Cochrane review) ✓ PubMed
Cochrane review found daily oral iron during pregnancy reduced maternal iron-deficiency anaemia at term (8.6% vs 19.8%; RR ~0.40) and maternal iron deficiency (RR ~0.47) versus placebo/no iron.
Systematic review USPSTF/Henderson 2024 (Systematic review) ✓ PubMed
USPSTF evidence review concluded routine prenatal iron supplementation reduces incidence of iron deficiency and iron-deficiency anaemia in pregnancy, but evidence for broader maternal/infant health outcomes is limited or shows no clear benefit.
Meta-analysis 2025 (Systematic review/Meta-analysis) ✓ PubMed
Meta-analysis of 11 RCTs (n=1,014) found only a small, non-significant haemoglobin advantage for daily over alternate-day oral iron (MD 0.28 g/dL, 95% CI -0.01 to 0.56), with comparable adverse effects, supporting alternate-day dosing as an option.
Meta-analysis Banerjee 2024 (Systematic review/Meta-analysis) ✓ PubMed
Systematic review and meta-analysis found daily and intermittent oral iron were similarly effective for preventing anaemia in pregnant women, while intermittent dosing tended to reduce gastrointestinal side effects.
Systematic review/Meta-analysis Anker 2023 (Systematic review/Meta-analysis) ✓ PubMed
Study-level meta-analysis of 10 RCTs (3,438 heart-failure patients with iron deficiency) found IV iron reduced the composite of CV death or first HF hospitalisation (RR 0.85, 95% CI 0.77-0.95) and total HF hospitalisations (RR 0.74, 95% CI 0.60-0.91), with no significant effect on all-cause or CV mortality.
Systematic review/Meta-analysis 2025 RLS (Systematic review/Meta-analysis) ✓ PubMed
Meta-analysis of 12 RCTs (511 patients) found iron supplementation, especially IV ferric carboxymaltose, significantly reduced International RLS scores (mean difference -5.28, 95% CI -7.66 to -2.90) and improved sleep and quality-of-life measures, though overall adverse events were modestly increased versus placebo.
Systematic review/Meta-analysis Gutema 2023 (Systematic review/Meta-analysis) ✓ PubMed
Meta-analysis of 12 RCTs (~3,105 school-age children) found iron supplementation significantly improved intelligence (SMD 0.46, 95% CI 0.19-0.73), attention (SMD 0.44) and memory (SMD 0.44) but not school achievement, with the largest benefits among children anaemic at baseline.
Cochrane review Nicholson (Cochrane) 2024 ✓ PubMed
Cochrane review of 13 trials (2002-2024) found IV iron in pregnancy likely increases haemoglobin slightly and reduces anaemia versus oral iron, with rare serious adverse events not increased.
Meta-analysis Ponikowski et al. 2023 (FCM IPD meta-analysis) ✓ PubMed
Individual patient data from 3 RCTs (n=4501) in HF with iron deficiency: IV ferric carboxymaltose reduced the composite of total CV hospitalisations and CV death (rate ratio 0.86, 95% CI 0.75-0.98; p=0.029), driven by fewer hospitalisations with no effect on mortality.
Systematic review Fernandez-Gaxiola & De-Regil 2019 (Cochrane) ✓ PubMed
Cochrane review of 25 RCTs (10,996 menstruating women): intermittent (1-3x/week) oral iron vs none/placebo cut anaemia risk (RR 0.65, 95% CI 0.49-0.87) and raised haemoglobin (+5.19 g/L) and ferritin; vs daily dosing it was similarly effective for anaemia with fewer adverse effects (RR 0.41, 95% CI 0.21-0.82).
RCT Düzen Oflas 2023 (RCT) ✓ PubMed
Double-blind RCT in 200 adults with iron-deficiency anaemia found no significant difference in haemoglobin rise between alternate-day (+1.05 g/dL) and daily (+1.36 g/dL) oral iron (p=0.47), nor in secondary tolerability outcomes.
RCT IVON Trial (Lancet Glob Health) 2024 ✓ Full text
Open-label RCT of 1,056 pregnant Nigerian women found IV ferric carboxymaltose did not significantly reduce anaemia at 36 weeks versus oral ferrous sulphate but improved iron-deficiency correction.
RCT Kalra 2022 IRONMAN (RCT) ✓ PubMed
In 1,137 UK heart-failure patients with iron deficiency, IV ferric derisomaltose narrowly missed significance for HF hospitalisation/CV death (RR 0.82, 95% CI 0.66-1.02) but was safe and well tolerated over a median 2.7 years.
RCT Stoffel et al. 2017 (two RCTs) ✓ PubMed
In iron-depleted women, alternate-day single-dose oral ferrous sulfate gave higher cumulative fractional iron absorption (21.8% vs 16.3%, p=0.0013) and total absorption (175.3 vs 131.0 mg, p=0.0010) than consecutive-day dosing; divided twice-daily dosing raised serum hepcidin and did not improve absorption. Demonstrates alternate-day, once-daily dosing optimises absorption.
Review Pasricha 2021 review ✓ Full text
Correcting deficiency improves fatigue and cognition.
Study Stoffel 2017 ✓ Source
Alternate-day dosing improved fractional iron absorption.
Study Clinical guidelines ✓ Source
Oral iron is first-line for iron-deficiency anemia.
17 sources cited · 17 verified Search all studies on PubMed ↗

Common questions about Iron

What is Iron used for?

Iron is most often taken for Treats iron-deficiency anemia, Restores energy (if deficient), Supports cognition. Critical for oxygen transport — supplement only if low.

Does Iron work — what does the evidence say?

Strong evidence. Multiple high-quality RCTs / meta-analyses with consistent effects. Iron is essential for hemoglobin and oxygen transport. Iron-deficiency anemia causes fatigue, poor concentration, and reduced exercise capacity, and supplementation reliably reverses it. Crucially, iron should only be supplemented when deficiency is confirmed — excess iron is pro-oxidant and dangerous, especially in conditions like hemochromatosis. Alternate-day dosing reduces side effects and may improve absorption.

What is the typical dose of Iron?

Treatment ~40–60 mg elemental; alternate-day dosing may absorb better. Test before supplementing.

Is Iron safe? Any cautions or side effects?

Constipation, nausea and dark stools are common. Overdose is dangerous and is a leading cause of pediatric poisoning. Excess iron is pro-oxidant and harmful in iron-overload conditions (e.g. haemochromatosis). Separate from calcium, antacids, levothyroxine and certain antibiotics (tetracyclines, fluoroquinolones), which it can bind. Never take without a confirmed need.

How many studies support Iron?

NutriDex cites 17 sources for Iron, graded "Strong".

Does Iron interact with any medications?

Yes — known or theoretical interactions include: Thyroid medication (levothyroxine) (caution). This is educational and not exhaustive; always check with your doctor or pharmacist before combining Iron with any medicine.

Cite this page
APA

Peh, D. (2026). Iron: Benefits, Dosage, Side Effects & Evidence. NutriDex — The Supplement Research Compendium. Retrieved 26 Jun 2026, from https://nutridex.info/s/iron

BibTeX
@misc{nutridex_iron,
  author       = {Peh, Daryl},
  title        = {Iron: Benefits, Dosage, Side Effects \& Evidence},
  year         = {2026},
  howpublished = {NutriDex --- The Supplement Research Compendium},
  url          = {https://nutridex.info/s/iron},
  note         = {Reviewed by Dr Daryl Peh, MBBS Singapore, MMed FM. Accessed 2026-06-26}
}

For medical claims, citing the underlying primary studies linked above is preferred. NutriDex is an educational reference, not medical advice.

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