nonhemejernabsorption

Nonheme iron absorption refers to the uptake of iron from nonheme dietary sources, which are iron not bound in a heme group. Most nonheme iron is in the ferric (Fe3+) form and is absorbed primarily in the duodenum and upper jejunum after reduction to the ferrous (Fe2+) form by brush-border enzymes such as ferrireductases. Inside enterocytes, iron may be stored as ferritin or exported by ferroportin into the portal circulation, where it is oxidized to Fe3+ by hephaestin and bound to transferrin. Systemic iron balance is regulated by hepcidin, which inhibits iron export by degrading ferroportin during inflammation or iron sufficiency.

Absorption is influenced by multiple factors. Enhancers include vitamin C and other reducing agents, organic acids, and the meat, poultry, fish factor, which can increase nonheme iron uptake. Inhibitors include phytates (common in legumes and cereals), polyphenols (tea, coffee, some coffees), calcium, and certain high-fiber components. Absorption rates vary widely, typically around 1–15% in iron-replete individuals, but can rise substantially in iron deficiency or increased demand.

Physiological status and health conditions modulate absorption. Iron-deficient individuals may absorb more nonheme iron, while inflammation increases hepcidin levels and reduces iron export, lowering absorption. Pregnancy and growth also affect requirements and uptake efficiency.

Dietary sources of nonheme iron include legumes, fortified cereals, grains, nuts, seeds, leafy greens, and dried fruits. Because many plant-based sources contain inhibitors, absorption can be enhanced by consuming vitamin C-rich foods with meals and by practices that reduce phytate content, such as soaking or fermenting. Nonheme iron differs from heme iron in that it is more sensitive to dietary factors and thus often requires different dietary strategies to optimize status.