Iron Absorption

Expansion

• Absorbed in the duodenum and upper jejunum
• Ferrous (Fe2+) iron is absorbed far better than ferric; vitamin C and gastric acid promote reduction and absorption, while phytates, tannins, calcium and antacids inhibit it
• Haem iron from meat is absorbed by a separate, more efficient route
• Enters the enterocyte through DMT1, and exits basolaterally through ferroportin

Hepcidin, made by the liver, is the master regulator: it binds ferroportin and causes its degradation, so iron is trapped in enterocytes and macrophages and not released into plasma.

• High hepcidin in iron overload and in inflammation, which is the mechanism of the anaemia of chronic disease: iron is present but sequestered
• Low hepcidin in iron deficiency, hypoxia and increased erythropoiesis

Because there is no regulated excretion, losing only 1 to 2 mg a day through desquamation and menstruation, absorption is the only control point. Failure of hepcidin signalling causes hereditary haemochromatosis, with unrestrained absorption and progressive tissue loading.