Absorption and Transport of Iron in Human Body
Entry of iron into the body us carefully regulated by its absorption, a very complex and poorly understood process. This regulation of absorption in the normal, healthy individual is closely tied to the level of the iron stores; absorption increases when iron stores are low and decreases as stores become greater. The rate of erythropoiesis also appears to influence iron absorption.
Food iron is presented to the body either as heme iron, found only in animal products, or as non-heme iron, which comprises all the iron occurring in plant foods and about 60% of that in animal foods.
Whether the iron is heme or non-heme has a major influence in the amount of the mineral absorbed. Since heme iron is so limited in most diets absorption of non-heme iron deserves the greater emphasis.
Overall absorption is estimated to range from 10 – 15%. Iron absorption can occur throughout the small intestine but is most efficient in the proximal portion, particularly the duodenum. Heme iron is absorbed as an intact metalloporphyrin, perhaps having first been split from global chain while in lumen of the gastrointestinal (GI) tract.
Heme is well absorbed but rates of absorption are inversely related to iron stores and may range form 15% to 35%. Within the mucosal cells the absorbed heme is broken down by a heme oxygenase, and the iron released moves through the mucosal cells in the form of small molecules.
The non-heme iron is less well absorbed with rate of absorption ranging from approximately 2% to 20%. Its specific rate of absorptions highly dependent on the amount of iron stores and the influence of concomitantly ingested dietary components.
Also affecting rate of absorption are existing conditions within the lumen of the proximal GI tract. The chemical form of the non-heme iron that enters the mucosal cells, the nature of receptor sties, and the trans-mucosal transport are unknown.
Absorption and Transport of Iron in Human Body
