Do vegan diets provide iron mainly as non-heme iron with lower bioavailability?

Individuals on vegan diets obtain dietary iron exclusively in the non-heme form. Because plant foods completely lack animal tissue, they contain 0% heme iron, which has distinct physiological implications for systemic iron status.

Clinical evidence and dietary guidelines

• Reduced absorption efficiency: Plant-based non-heme iron has a fractional absorption rate of only 5% to 15% (dropping as low as 5% to 12% in strictly vegan diets), whereas animal-derived heme iron features a significantly higher absorption rate of 15% to 35%.
• Impact on iron stores: Because of this lower bioavailability, individuals consuming vegan diets frequently present with lower serum ferritin levels and depleted iron stores compared to omnivores, even when their total daily iron intake is equivalent or higher.
• Elevated intake targets: To compensate for these absorption differences, major nutritional guidelines recommend that vegetarians and vegans target an iron intake approximately 1.8 times higher than the standard recommended dietary allowance (RDA).

Mechanistic pathways and dietary sensitivity

• Uptake pathways: Non-heme iron enters the gut in the insoluble ferric ($Fe^{3+}$) state and must be reduced to the absorbable ferrous ($Fe^{2+}$) state by duodenal cytochrome B (Dcytb) before transport across the apical membrane via divalent metal transporter 1 (DMT1). In contrast, heme iron is absorbed intact via heme carrier protein 1 (HCP1), bypassing these luminal steps.
• Vulnerability to inhibitors: This reduction-dependent pathway makes non-heme iron highly vulnerable to luminal chelators. Co-ingesting even small amounts (2 to 25 mg) of phytates from grains or legumes reduces absorption by 18% to 64% (and up to 80% at higher doses), while a single cup of tea or coffee reduces absorption by 60% to 70% and 40%, respectively.
• Counteraction by enhancers: Co-ingesting 30 to 100 mg of Vitamin C (ascorbic acid) chemically reduces ferric iron back to the highly soluble ferrous state, which doubles or triples non-heme iron absorption and successfully overcomes phytate inhibition.

Bottom line

• Vegan diets provide iron exclusively as non-heme iron, which is substantially less bioavailable than animal-sourced heme iron and is uniquely sensitive to being heavily suppressed by dietary phytates and polyphenols or strongly enhanced by Vitamin C.