Iron: Heme vs. Non-Heme, Absorption Enhancers & Blockers
Iron is essential for oxygen transport (in hemoglobin), energy production (in cytochromes), and immune function. Iron deficiency is the most common nutrient deficiency worldwide, affecting an estimated 1.6 billion people. Yet iron absorption is one of the most tightly regulated and influenced processes in human nutrition.
Heme vs. Non-Heme Iron
Dietary iron comes in two forms: heme iron (from animal hemoglobin and myoglobin in meat, poultry, and fish) and non-heme iron (from plant foods, fortified foods, and supplements). Heme iron is absorbed at 15-35% efficiency and is relatively unaffected by other dietary components. Non-heme iron absorption ranges from 2-20% and is heavily influenced by enhancers and inhibitors in the same meal.
Absorption Enhancers
Vitamin C is the most potent enhancer of non-heme iron absorption, reducing ferric iron to the more absorbable ferrous form. Consuming 75 mg of vitamin C (about one bell pepper or cup of strawberries) with a meal can increase non-heme iron absorption 3-6 fold. Organic acids in fruits and fermented foods also help. The "meat factor" in animal protein enhances non-heme iron absorption through mechanisms that aren't fully understood.
Absorption Blockers
Phytic acid in grains, legumes, nuts, and seeds can reduce non-heme iron absorption by up to 80%. Tannins in tea, coffee, and wine bind iron in the gut. Oxalates and calcium (when consumed in the same meal) also reduce iron absorption. Polyphenols broadly can inhibit absorption, which creates an interesting tension with their health benefits.
Iron Overload
Because the body has no regulated excretion pathway for iron, excess intake (especially from supplements and fortified foods) can lead to accumulation. Hereditary hemochromatosis affects roughly 1 in 200-300 people of Northern European descent and causes enhanced iron absorption. Iron supplementation should be based on actual iron status testing, not assumed need.
External resources: NIH — Iron Fact Sheet