Iron absorbed where

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Iron Absorption in the Human Body

Iron is a crucial element for various physiological functions, including oxygen transport, energy metabolism, and cell division. Understanding where and how iron is absorbed in the human body is essential for addressing iron deficiency and optimizing dietary intake.

Primary Site of Iron Absorption: Duodenum and Jejunum

The duodenum and proximal jejunum are the primary sites for iron absorption in the human body. Studies have shown that iron is absorbed along the entire small intestine, but the efficiency is highest in the duodenum and proximal jejunum 15. In iron-deficient individuals, enhanced absorption extends distally to about the mid-jejunum .

Mechanisms of Iron Absorption

Iron absorption involves several mechanisms and pathways:

Heme Iron Absorption: Heme iron, derived from hemoglobin and myoglobin in the diet, is absorbed intact by the intestinal mucosa. The absorbed heme is then cleaved by mucosal heme oxygenase, releasing inorganic iron . This process is most active in the duodenum, where heme oxygenase activity is highest .
Non-Heme Iron Absorption: Non-heme iron is absorbed via different pathways. Ferric iron (Fe3+) is absorbed through a pathway involving integrin and mobilferrin, while ferrous iron (Fe2+) uptake is facilitated by the divalent metal transporter 1 (DMT1) . Other proteins, such as Stimulator of Iron Transport (SFT) and Hephaestin, also play roles in iron uptake and transfer from enterocytes to plasma .

Factors Influencing Iron Absorption

Several factors influence the efficiency of iron absorption:

Iron Status: The body's iron status significantly affects absorption rates. Iron-deficient individuals absorb a higher percentage of dietary iron compared to those with sufficient iron levels 89. This adaptive mechanism ensures that iron absorption increases when the body's iron stores are low.
Dietary Enhancers and Inhibitors: Certain dietary components can enhance or inhibit iron absorption. Ascorbic acid (vitamin C) and proteins enhance non-heme iron absorption, while calcium, phytates, and polyphenols inhibit it . For instance, tea has been shown to inhibit non-heme iron absorption significantly .
Form of Iron: Heme iron is generally absorbed more efficiently than non-heme iron. Studies have shown that a greater fraction of heme iron is absorbed compared to non-heme iron from the diet .

Conclusion

Iron absorption primarily occurs in the duodenum and proximal jejunum, with various mechanisms facilitating the uptake of heme and non-heme iron. The efficiency of iron absorption is influenced by the body's iron status, dietary components, and the form of iron consumed. Understanding these factors is crucial for developing strategies to improve iron bioavailability and address iron deficiency.

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Most relevant research papers on this topic

Site of iron absorption in man.

Iron absorption in humans occurs throughout the small intestine, with the proximal jejunum being more efficient in normal individuals and enhanced absorption in iron deficiency.

Non-RCT

2009·

49citations

·Munsey S. Wheby

Iron absorption and transport—An update

Iron absorption and transport are tightly regulated to maintain an equilibrium between absorption and body loss, with various proteins playing key roles in iron absorption and transport.

Highly Cited

2000·

264citations

·M. Conrad et al.

RADIOACTIVE IRON ABSORPTION BY GASTRO-INTESTINAL TRACT

Chronic anemia in dogs leads to significant iron absorption, with variations in absorption peaks and duration, and a complex protein metabolism influencing iron acceptance.

Highly Cited

1943·

296citations

·P. Hahn et al.

The absorption of iron from whole diets: a systematic review.

Dietary iron absorption is higher with enhancers and low-bioavailability diets, with variations between studies and influenced by iron status, dietary enhancers, and inhibitors.

Systematic ReviewVery Rigorous JournalHighly Cited

2013·

146citations

·R. Collings et al.

Intestinal absorption of hemoglobin iron-heme cleavage by mucosal heme oxygenase.

Mucosal heme oxygenase plays an important role in the absorption of hemoglobin iron in the intestinal mucosa, with its activity increasing in iron deficiency.

Non-RCTAnimal StudyHighly Cited

1974·

213citations

·S. B. Raffin et al.

Iron Absorption: Factors, Limitations, and Improvement Methods

Iron absorption is crucial for human health, but current methods and research are focused on improving iron bioavailability and combating iron deficiency.

Highly Cited

2022·

206citations

·Elif Piskin et al.

Food iron absorption in man. Applications of the two-pool extrinsic tag method to measure heme and nonheme iron absorption from the whole diet.

The two-pool extrinsic tag method accurately measures iron absorption from a mixed diet, with a greater fraction of heme iron absorbed (37%), and increased iron fortification levels significantly increase absorption.

Non-RCTHighly Cited

1974·

216citations

·E. Björn-Rasmussen et al.

Iron absorption. Measurement of ingested iron59 by a human whole-body liquid scintillation counter.

Iron absorption in normal adults is lO% or less, while iron-deficient individuals absorb 29 to 71%, providing an index of iron loss, including loss by bleeding.

Non-RCT

1961·

48citations

·R. VAN HOEK et al.

The absorption of radioiron labeled foods and iron salts in normal and iron-deficient subjects and in idiopathic hemochromatosis.

Absorption of radioiron-labeled foods and iron salts is significantly higher in normal subjects than in iron-deficient individuals and those with idiopathic hemochromatosis.

Non-RCTHighly Cited

1957·

84citations

·R. Chodos et al.

Iron absorption in the thalassemia syndromes and its inhibition by tea.

Tea effectively inhibits iron absorption, potentially benefiting patients with thalassemia intermedia.

Non-RCTHighly Cited

1979·

113citations

·P. A. de Alarcón et al.

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