Iron (Heme & Non-Heme)

Direct Answer

Iron is an essential redox trace element central to hemoglobin oxygen transport, myoglobin storage, and mitochondrial electron transport chain cytochromes. Adult RDA is 8mg (men/post-menopausal women) / 18mg (pre-menopausal women), with a Tolerable Upper Limit of 45mg/day.

Source: NIH Office of Dietary Supplements / WHO · Last reviewed Aug 28, 2026

Specs

Nutrient Type	Essential Trace Mineral
Adult RDA / RDI	8 mg (Men) / 18 mg (Women 19–50) / 27 mg (Pregnancy)
Tolerable Upper Limit (UL)	45 mg / day (Hemochromatosis / Fenton reaction oxidative stress)
Chemical Forms	Heme Iron (Fe2+ Porphyrin - Animal), Non-Heme Iron (Fe3+ Ferric / Fe2+ Ferrous - Plants/Supplements)
Primary Biological Function	Hemoglobin O2 transport, Myoglobin O2 storage, Cytochrome c electron transport, Catalase
Deficiency Condition	Microcytic Hypochromic Anemia, Severe fatigue, Restless legs syndrome, Pica
Top Whole Food Sources	Beef Liver, Oysters, Duck Breast, Beef Ribeye, Lentils, Spinach, Dark Chocolate
Bioavailability Difference	Heme: 15–35% absorption (uninhibited); Non-Heme: 2–20% (inhibited by phytates/calcium, boosted by Vitamin C)

Hepcidin Systemic Iron Master Regulator

The liver secretes hepcidin peptide in response to elevated systemic iron or systemic inflammation. Hepcidin binds to and degrades ferroportin export channels, blocking intestinal iron absorption and trapping iron in macrophage storage.