How do you digest iron?

The absorption of dietary iron is a tightly regulated process that involves multiple steps. The majority of iron in the diet is in the form of ferric iron (Fe3+), which is not readily absorbed. The following are the main steps of iron digestion and absorption:

1. Reduction of Iron: In the stomach, ferric iron (Fe3+) is reduced to ferrous iron (Fe2+) by gastric juices, specifically hydrochloric acid and the enzyme gastric ascorbic acid (vitamin C). This reduction is essential for iron absorption.

2. Binding to Gastric Proteins: Once reduced, ferrous iron binds to gastric proteins, such as transferrin and lactoferrin. These proteins help protect the iron from further oxidation and facilitate its transport to the small intestine.

3. Transport to the Small Intestine: The stomach contents, including the iron-protein complexes, are passed to the small intestine, primarily the duodenum.

4. Brush Border Reduction and Uptake: In the duodenum, the brush border membrane of enterocytes (intestinal cells) contains specific proteins that facilitate the absorption of ferrous iron. These proteins include the divalent metal transporter 1 (DMT1), which transports iron across the brush border membrane into the enterocyte.

5. Intracellular Storage and Transport: Inside the enterocyte, iron is stored in ferritin, a protein that sequesters iron in a non-toxic form. When body iron stores are low, iron is released from ferritin and exported out of the enterocyte into the bloodstream.

6. Export into the Bloodstream: Iron is transported out of the enterocyte into the bloodstream by a protein called ferroportin. Ferroportin is located on the basolateral membrane of the enterocyte and facilitates the export of ferrous iron.

7. Oxidation and Binding to Transferrin: Once in the bloodstream, ferrous iron is rapidly oxidized back to ferric iron (Fe3+). This oxidation is facilitated by the enzyme ceruloplasmin. Ferric iron then binds to transferrin, a plasma protein that transports iron throughout the body to various tissues and cells.

The regulation of iron absorption is a complex process that involves several hormones and regulatory mechanisms. The body tightly controls iron absorption to maintain iron homeostasis and prevent iron deficiency or iron overload.