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📰Read the full Iron evidence review on GMJ News →Complete clinical article, references and updates on news.gmj.ge. This page is the structured safety summary.⚠ Iron supplementation in iron-replete patients may increase cardiovascular and cancer risk — always document deficiency before prescribing [1].
⚠ Separate from levothyroxine by 4 hours, fluoroquinolones and tetracyclines by 2 hours [1].
⚠ PPIs reduce non-heme iron absorption significantly. Consider IV iron in PPI-dependent patients with refractory deficiency [1].
🥗 Food first — build your daily 8 mg/ 18 mg
Check the foods you regularly eat — the bar fills toward your daily target.
Oysters (85g)8 mg
Beef liver (85g)5 mg
Beef (85g)2.6 mg
Fortified cereals (1 serving)18 mg
White beans (½ cup)3.9 mg
Lentils (½ cup cooked)3.3 mg
Spinach (½ cup cooked)3.2 mg
Dark chocolate (28g)3.4 mg
Check your regular foods above
☑ Risk checker
Premenopausal women (menstrual blood loss) [1]
Pregnancy (expanded blood volume) [1]
Vegetarians and vegans (non-heme iron only) [1]
Frequent blood donors [1]
Celiac disease and inflammatory bowel disease [1]
Chronic kidney disease [1]
Heavy exercise (especially runners: foot-strike hemolysis)
Infants 6–12 months (rapid growth phase) [1]
Select factors
🔬 Lab interpreter
Recommended test
Serum ferritin
Serum ferritin
Reference range / target
<15 ng/mL = depleted stores (high specificity). <30 ng/mL = likely deficiency in context of symptoms. Note: ferritin is an acute phase reactant — elevated in inflammation; may be falsely normal/high in iron-deficient patients with concurrent infection or inflammation [3]
<15 ng/mL = depleted stores (high specificity). <30 ng/mL = likely deficiency in context of symptoms. Note: ferritin is an acute phase reactant — elevated in inflammation; may be falsely normal/high in iron-deficient patients with concurrent infection or inflammation [3]
When to test
First-line for iron stores; all suspected iron deficiency; menstruating women with fatigue; post-bariatric
Full lab monitoring ↓First-line for iron stores; all suspected iron deficiency; menstruating women with fatigue; post-bariatric
⚕ For professionals — confirm ranges against your local laboratory.
Clinical verdict
Test ferritin before prescribing — never supplement empirically. Iron is a pro-oxidant; supplementation in replete patients (ferritin >200 ng/mL) increases oxidative stress [1]. Every-other-day dosing matches daily dosing for hemoglobin recovery with superior tolerability and fractional absorption [3]. Ferrous bisglycinate: equivalent efficacy, fewer GI side effects than sulfate. Always co-prescribe vitamin C [1].
1 How much do I need?
👤 Adults: Specific dosage data under clinical review
👴 Elderly: Specific dosage data under clinical review
🤰 Pregnancy: Specific dosage data under clinical review
👦 Pediatric: Specific dosage data under clinical review
🏃 Athletes: Specific dosage data under clinical review
⚖️ Obesity: Standard dose
Fat-soluble compounds may require dose adjustment in obesity.
🩺 Renal: Consult specialist
Dose adjustment may be needed in renal impairment.
🌱 Vegan: Specific dosage data under clinical review
How to take
🍽 Timing: Best absorbed on empty stomach (1 hour before meals). Take every other day for better fractional absorption (hepcidin rebound allows 24–48h recovery) [6].
💊 With food: Take with vitamin C (200 mg) to enhance absorption. Avoid taking with dairy, calcium supplements, tea, coffee, or whole grains within 1 hour [1].
🚫 Avoid: Do not take with levothyroxine, antacids, fluoroquinolones, tetracyclines, or calcium supplements. Separate by 2–4 hours [5].
2 Which form?
| Form | Bioavailability | Vegan | Cost |
|---|---|---|---|
| ['Ferrous sulfate', 'preferred', 'Most studied form. Contains 20% elemental iron. Best absorbed on an empty stomach but commonly causes GI side effects (nausea, constipation). First-line treatment for iron deficiency anemia [1].'] | Standard | Check label | |
| ['Ferrous bisglycinate', '', 'Chelated amino acid form. Equivalent efficacy to ferrous sulfate with fewer GI side effects in comparative trials. Higher cost.'] | Standard | Check label | |
| ['Ferrous fumarate', '', 'Contains 33% elemental iron (highest of oral forms). Similar efficacy and side effect profile to ferrous sulfate.'] | Standard | Check label | |
| ['Iron polysaccharide complex', '', 'Better tolerated but lower bioavailability. Suitable for individuals who cannot tolerate ferrous salts.'] | Standard | Check label |
3 Common questions
Should I take iron supplements? ▼
Only if you have documented iron deficiency (ferritin below 30 ng/mL) or iron deficiency anemia. Iron is a pro-oxidant, and supplementation in iron-replete individuals may increase oxidative stress and is associated with increased cardiovascular and cancer risk in observational studies [1]. Always test ferritin levels before starting iron supplementation.
Why does iron cause constipation and stomach upset? ▼
Unabsorbed iron in the GI tract generates free radicals through Fenton reactions, causing oxidative damage to the intestinal mucosa. This produces nausea, abdominal pain, and constipation in 30–50% of users [1]. Strategies to reduce side effects: take with food (reduces absorption by 40% but improves tolerability), use every-other-day dosing [3], or switch to ferrous bisglycinate.
How can I increase iron absorption from plant foods? ▼
Consume vitamin C with iron-rich meals (a glass of orange juice increases non-heme absorption 2–3 fold). Cook in cast iron cookware (increases iron content of acidic foods). Soak and sprout legumes to reduce phytate content. Avoid tea, coffee, and calcium supplements within 2 hours of iron-rich meals [1].
How long does it take to correct iron deficiency? ▼
With appropriate oral supplementation (100–200 mg elemental iron per day), hemoglobin typically normalizes within 6–8 weeks. Complete ferritin repletion requires 3–6 months of continued supplementation [1]. Intravenous iron is indicated when oral therapy fails or is not tolerated.
4 Clinical evidence
Strong
Treatment of iron deficiency anemia: oral iron supplementation (100–200 mg elemental iron/day) normalizes hemoglobin in 6–8 weeks and replenishes ferritin stores in 3–6 months [1]. Every-other-day dosing (versus daily) produces comparable hemoglobin recovery with better tolerability and fractional absorption, as demonstrated in a randomized crossover trial using stable iron isotopes [3]. HIGH
Moderate
Cognitive development in iron-deficient children: supplementation improves attention and concentration scores, particularly in anemic school-age children in low-income settings [2]. Exercise performance: iron repletion in deficient (but non-anemic) female athletes improves endurance and reduces perceived exertion [1]. MODERATE
Insufficient
Cancer prevention: iron supplementation does not reduce cancer risk and may increase risk in iron-replete individuals (ferritin >200 ng/mL) based on observational data [1]. Immune enhancement in non-deficient populations: no benefit demonstrated; excess iron may paradoxically impair immune function [1]. LOW
5 Safety, toxicity & adverse events
Absolute contraindications
✕ Hemochromatosis (hereditary or secondary) — iron loading worsens organ damage
✕ Hemosiderosis — excess iron already deposited in tissues
✕ Hemolytic anemias with iron overload (thalassemia major on transfusions)
Relative
⚠ Peptic ulcer disease — oral iron irritates GI mucosa
⚠ Inflammatory bowel disease — exacerbates GI symptoms, may worsen inflammation
⚠ Concurrent fluoroquinolone or tetracycline antibiotics — iron chelates these drugs (separate by 2+ hours)
🚩 Red flags
● Iron supplementation without documented deficiency in men or postmenopausal women — screen for hemochromatosis first [3]
● Ferritin <15 with normal MCV — iron deficiency without anemia; still warrants treatment [3]
● Iron deficiency refractory to oral supplementation — consider celiac disease, H. pylori, or occult GI bleeding [3]
● Child with access to adult iron supplements — accidental overdose is a medical emergency [1]
● New iron deficiency in adult male or postmenopausal female — exclude GI malignancy (colonoscopy/endoscopy) [3]
● Elevated ferritin with low TSAT — anemia of chronic disease, not iron deficiency [3]
6 Interactions
Drug interactions
Levothyroxine Major
Mechanism: Iron forms insoluble complex with levothyroxine, reducing absorption by 30–65%. Clinically significant — can cause hypothyroid symptoms [5].
Fluoroquinolone antibiotics Major
Mechanism: Fe²⁺/Fe³⁺ chelates fluoroquinolones (ciprofloxacin, levofloxacin) reducing absorption by 30–60% [5].
Tetracycline antibiotics Major
Mechanism: Iron chelation reduces tetracycline absorption and vice versa [5].
Levodopa/carbidopa Moderate
Mechanism: Iron chelates levodopa, reducing its bioavailability [5].
Bisphosphonates (alendronate) Moderate
Mechanism: Iron chelation reduces bisphosphonate absorption [5].
Proton pump inhibitors Moderate
Mechanism: Gastric acid suppression impairs conversion of Fe³⁺ to absorbable Fe²⁺; reduces non-heme iron absorption [5].
7 Regulatory
United States (FDA): Dietary supplement (OTC). Iron-containing supplements must carry a warning label about accidental overdose risk in children (leading cause of poisoning death in children under 6 in the US historically).
European Union (EFSA): Authorized health claims for cognitive function, oxygen transport, immune function, energy metabolism, and red blood cell formation. Upper limit: 45 mg/day (from supplements).
Japan (MHLW): Listed nutrient with function claims permitted. Adequate intake: 7.5 mg/day (men), 10.5 mg/day (premenopausal women).
World Health Organization: Iron supplementation recommended for all pregnant women in high-prevalence settings. Iron deficiency classified as the most common nutritional disorder globally [2].
8 US supplement products
2,238
on-market products containing Iron (NIH DSLD)
Brands carrying Iron (584)
Click a brand to see its Iron products.
9 Frequently paired with
10 Cite this page
Vancouver: Pkhakadze G. Iron — safety profile [Internet]. Tbilisi: PHIG; 2026 [cited 2026 Jul 15]. Available from: https://supplement.ge/ingredients/iron/
APA 7th: Pkhakadze, G. (2026). Iron — Safety profile. Public Health Institute of Georgia. https://supplement.ge/ingredients/iron/
📋 Editorial information
Author: Prof. G. Pkhakadze, MD, MPH, PhD
Institution: Public Health Institute of Georgia (PHIG)
Affiliation: David Tvildiani Medical University (DTMU)
First published: January 2026
Last reviewed: 2026-05-29
Next review: January 2027
References: 3 cited sources
COI: SupplementIndex receives no funding from supplement manufacturers. All content independently authored by PHIG.
Process: Systematic literature review
📄 License & reuse
Published under Creative Commons Attribution 4.0 International (CC BY 4.0). You may share and adapt for any purpose with attribution.
Pkhakadze G. "Iron — Safety Profile." SupplementIndex, PHIG, 2026. https://supplement.ge/ingredients/iron/ CC BY 4.0.
GP
Prof. G. Pkhakadze, MD, MPH, PhD
Professor of Public Health · Head of Department, DTMU
Editor-in-Chief, Georgian Medical Journal (ISSN 3088-4322)
Chair, Public Health Institute of Georgia · UEMS Public Health Section
Educational and public health purposes. CC BY 4.0. Consult your healthcare provider before starting any supplement. Corrections: info@accreditation.ge. Publisher: PHIG