Iron
Essential mineral for oxygen transport via hemoglobin and myoglobin. Iron deficiency is the most common nutritional deficiency worldwide, affecting approximately 2 billion people.
What is Iron?
Iron is an essential mineral that forms the functional core of hemoglobin (in red blood cells) and myoglobin (in muscle), enabling oxygen transport throughout the body. It also serves as a cofactor for enzymes involved in energy metabolism, DNA synthesis, and immune defense.
Known Health Benefits
How It Works
Iron exists in two oxidation states (Fe²⁺ and Fe³⁺), enabling electron transfer in cytochromes and oxidative phosphorylation. Hepcidin, produced by the liver, is the master regulator of iron homeostasis — it controls ferroportin-mediated iron export from enterocytes and macrophages. Iron is absorbed primarily in the duodenum; heme iron from animal sources is absorbed 15–35% vs 2–20% for non-heme iron from plants. Vitamin C converts Fe³⁺ to Fe²⁺, markedly enhancing non-heme absorption.
What Research Says
A 2016 Lancet Global Health review estimated 1.24 billion people have iron-deficiency anemia. A 2015 meta-analysis in JAMA confirmed that IV iron significantly improved fatigue, exercise capacity, and quality of life in heart failure patients with iron deficiency even without anemia. Ferrous bisglycinate studies show comparable efficacy to ferrous sulfate with significantly fewer GI side effects.
Active Compounds
Ferrous sulfate, ferrous bisglycinate (gentlest), ferric iron
Forms & Bioavailability
Heme iron (animal sources) is absorbed at 15–35% regardless of dietary factors. Non-heme iron absorption ranges from 2–20% and is enhanced by vitamin C, meat factor, and organic acids, while inhibited by phytates, polyphenols (tea/coffee), calcium, and fiber. Ferrous bisglycinate chelate is absorbed 2–4× better than ferrous sulfate.
Dosage Guidance
| Use Case | Dosage |
|---|---|
| Iron-deficiency anemia (treatment) | 100–200 mg elemental iron |
| Iron repletion (low ferritin, no anemia) | 25–65 mg elemental iron |
| Pregnancy | 27–60 mg elemental iron |
| Menstruating women (prevention) | 18 mg elemental iron |
| Athletes (endurance) | 15–30 mg elemental iron |
Always consult a healthcare provider for personalized dosing.
Natural Food Sources
- Beef liver (5 mg per 3 oz — heme iron)
- Oysters (8 mg per 3 oz — heme iron)
- Spinach (3.2 mg per ½ cup cooked — non-heme)
- Lentils (3.3 mg per ½ cup — non-heme)
- Fortified cereals (8–18 mg per serving)
- Dark chocolate (3.4 mg per oz — non-heme)
Potential Side Effects
Constipation, nausea, dark stools; significant toxicity risk with overdose — keep away from children
Who Should Avoid It
- Hemochromatosis or hereditary iron overload disorders
- Hemolytic anemias (thalassemia, sickle cell receiving transfusions) — iron overload risk
- Iron supplementation without confirmed deficiency — excess iron is pro-oxidant
- Active GI bleeding — address underlying cause first
Pregnancy & Lactation
Iron supplementation is a cornerstone of prenatal care. The RDA increases to 27 mg during pregnancy due to expanded blood volume and fetal demands. WHO recommends 30–60 mg daily in pregnancy. Iron is present in breast milk; lactation RDA is 9 mg. Ferrous bisglycinate is preferred for tolerability.
Known Drug Interactions
Reduces absorption of levothyroxine, tetracycline antibiotics, and quinolones (separate by 2–4 hours)
Evidence Classification
Supported by randomized controlled trials (RCTs), systematic reviews, or meta-analyses published in peer-reviewed journals.
Frequently Asked Questions
Why does iron supplementation cause constipation?
Unabsorbed iron in the colon changes gut motility and the microbiome. Ferrous sulfate is the worst offender. Switching to ferrous bisglycinate, taking iron every other day, or adding magnesium can help.
Should I take iron with or without food?
Empty stomach maximizes absorption (up to 3× more), but many people cannot tolerate it. Taking iron with a small amount of food plus vitamin C (e.g., orange juice) is a practical compromise.
Why is every-other-day dosing now recommended?
Research published in The Lancet Haematology (2017) showed that hepcidin rises sharply after an iron dose and stays elevated for 24 hours, blocking absorption of a second dose. Alternate-day dosing avoids this rebound and actually increases total iron absorption.
How long does it take to correct iron deficiency?
Hemoglobin typically improves within 2–4 weeks. Ferritin normalization takes 3–6 months of supplementation. Continue supplementation for at least 3 months after ferritin reaches target (typically > 50 ng/mL).
Can I take iron and thyroid medication together?
No. Iron significantly reduces levothyroxine absorption. Take thyroid medication first thing in the morning on an empty stomach, and wait at least 4 hours before taking iron.
What is the difference between heme and non-heme iron?
Heme iron comes from animal sources and is absorbed at 15–35% regardless of other dietary factors. Non-heme iron from plants is absorbed at only 2–20% and is affected by enhancers (vitamin C) and inhibitors (phytates, tannins).
Is too much iron dangerous?
Yes. Iron is a pro-oxidant and excess iron catalyzes free radical formation. Never supplement iron without confirmed deficiency via blood tests (serum ferritin, TIBC, transferrin saturation). Acute overdose is a medical emergency, especially in children.
References
- Iron deficiency anaemia: assessment, prevention and control — a guide for programme managers. World Health Organization. WHO Technical Report (2001)View study
- Iron therapy for the treatment of iron deficiency in chronic heart failure: intravenous or oral?. Anker SD, Comin Colet J, Filippatos G, et al.. European Journal of Heart Failure (2017)View study
- Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split doses. Stoffel NU, Cercamondi CI, Brittenham G, et al.. The Lancet Haematology (2017)View study
- The global prevalence of anaemia in 2011. Stevens GA, Finucane MM, De-Regil LM, et al.. The Lancet Global Health (2013)View study
Related Health Conditions
Related Supplements
Have questions about Iron?
Ask Mother Nature AI about dosing, interactions with your medications, whether it fits your health goals, and more — personalized to your health profile.
This entry is for educational purposes only. It is not medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement regimen, especially if you take medications or have health conditions.