Iron
Essential for oxygen transport, energy production, and immune function — but supplementation requires care.
Also known as: Ferrous Sulfate • Iron Bisglycinate • Ferrous Fumarate
Overview
Iron is an essential mineral that plays a central role in oxygen transport (as part of hemoglobin), energy production, DNA synthesis, and immune function. Iron deficiency is the most common nutritional deficiency worldwide, affecting an estimated 2 billion people. Women of reproductive age, pregnant women, vegetarians/vegans, endurance athletes, and frequent blood donors are at highest risk. However, iron supplementation should be approached carefully — unlike most supplements, excess iron can be harmful, and supplementation should ideally be guided by blood test results.
Key Benefits
Oxygen Transport
Iron is the central atom in hemoglobin, the protein in red blood cells that carries oxygen from the lungs to every cell in the body. Iron deficiency leads to anemia — reduced oxygen-carrying capacity that causes fatigue, weakness, shortness of breath, and pale skin.
Energy Production
Iron is a component of cytochromes in the electron transport chain, essential for ATP (energy) production. Iron deficiency causes fatigue even before anemia develops, because cellular energy production is impaired.
Immune Function
Iron is required for immune cell proliferation and maturation, particularly lymphocytes. Iron deficiency impairs immune function and increases susceptibility to infections.
Cognitive Function
The brain requires significant iron for neurotransmitter synthesis (dopamine, serotonin, norepinephrine) and myelin production. Iron deficiency in children impairs cognitive development, and in adults causes brain fog and poor concentration.
Dosage & How to Take
Only supplement iron if blood tests confirm deficiency. The RDA is 18mg for premenopausal women and 8mg for men and postmenopausal women.
| Purpose | Dose | Notes |
|---|---|---|
| Mild deficiency | 18–30 mg/day | Iron bisglycinate; retest in 3 months |
| Moderate deficiency | 30–65 mg/day | May need 3–6 months to replenish stores |
| Severe deficiency/anemia | 65–200 mg/day | Under medical supervision; may need IV iron |
| Maintenance (at-risk groups) | 18 mg/day | Premenopausal women, vegetarians |
Best Time to Take
On empty stomach for best absorption; with vitamin C to enhance absorption
With or Without Food
Empty stomach is ideal but causes more GI upset; with food if needed (avoid dairy, coffee, tea)
Forms & Bioavailability
| Form | Absorption | Best For | Notes |
|---|---|---|---|
| Iron Bisglycinate (Chelated) | Excellent | Most people | Gentlest on stomach; best absorbed; doesn't require empty stomach |
| Ferrous Sulfate | Good | Budget option, severe deficiency | Most common prescription form; more GI side effects |
| Ferrous Fumarate | Good | Higher elemental iron per dose | 33% elemental iron; more GI side effects than bisglycinate |
| Iron Polysaccharide Complex | Good | Sensitive stomachs | Less GI upset than ferrous salts; slower absorption |
Side Effects & Safety
Common
- Constipation
- Nausea
- Dark/black stools
- Stomach cramps
Rare
- Vomiting
- Diarrhea
- Iron overload (with excessive supplementation)
Contraindications
- Hemochromatosis (iron overload disorder)
- Hemolytic anemias
- Repeated blood transfusions
- Do not supplement without confirmed deficiency
Interactions
Enhances iron absorption by up to 67% — take together
Calcium inhibits iron absorption — take 2+ hours apart
Tannins and polyphenols reduce iron absorption by 50–90%
Iron reduces levothyroxine absorption — take 4+ hours apart
Scientific Research
Iron Bisglycinate vs Ferrous Sulfate
Iron bisglycinate had equivalent efficacy with 50% fewer GI side effects
Iron and Cognitive Function
Iron supplementation improved attention, concentration, and IQ scores in iron-deficient women
Alternate-Day Dosing
Taking iron every other day improved absorption by 34% compared to daily dosing
Food Sources
Frequently Asked Questions
Medical Disclaimer
This content is for educational and informational purposes only and is not intended as medical advice. Always consult with a qualified healthcare professional before starting any supplement regimen, especially if you have pre-existing health conditions or are taking medications. The statements on this page have not been evaluated by the Food and Drug Administration.