Forms of Iron

Forms of Iron

Iron comes in 2 forms: heme iron (from meat and animal products) and non-heme iron (from other sources like vegetables and iron supplements). Non-heme iron used in iron supplements can appear in 3 forms:

  • Ferric iron—This type of iron is less soluble than ferrous iron when the acidity in the stomach is low. It has to be converted to ferrous iron (Fe2+) so that it can be dissolved and absorbed in the small intestine.
  • Ferrous iron—Ferrous iron is more soluble and easier to absorb than ferric iron. It is frequently used in iron supplements as ferrous sulfate, ferrous gluconate, and ferrous fumarate.
  • Carbonyl iron—Carbonyl iron is a pure form of iron that is widely used as a food additive and has been studied for the treatment of iron deficiency anemia.1,2 When ingested, it requires gastric acid from the stomach to become soluble. Gastric acid converts the carbonyl iron to ferrous iron, and once this happens, it is absorbed in the same manner as ferrous iron.1 Because carbonyl iron is dependent upon gastric acid for absorption, it is less toxic and better tolerated than other forms of iron.1,2

1 Gordeuk VR, Brittenham GM, Hughes M, Keating LJ, Opplt JJ. High-dose carbonyl iron for iron deficiency anemia: a randomized double-blind trial. Am J Clin Nutr. 1987;46(6):1029-1034.

2 Gordeuk VR, Brittenham GM, McLaren CE, Hughes MA, Keating LJ. Carbonyl iron therapy for iron deficiency anemia. Blood. 1986;67(3):745-752.