Iron absorption rate in the human body
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Iron Absorption Rate in the Human Body: Key Factors and Ranges
Average Iron Absorption Rates in Healthy Adults
In healthy adults with normal iron stores, the body typically absorbs about 8–10% of the iron from an oral dose, with no significant difference between males and females. This has been confirmed by studies using whole-body counting and red cell incorporation methods, which found geometric mean absorption rates of 8.5% in healthy subjects, and less than 10% in iron-replete adults 12.
Increased Absorption in Iron Deficiency
Iron absorption rates rise significantly in individuals who are iron-deficient. In these cases, absorption can range from 29% up to 71%, reflecting the body’s increased need for iron and its ability to regulate absorption accordingly .
Dietary Iron Bioavailability and Influencing Factors
The type of diet greatly affects iron absorption. For mixed diets (including both plant and animal sources), iron bioavailability is estimated at 14–18%. For vegetarian diets, the range is lower, at 5–12%, due to the absence of heme iron and the presence of more inhibitors 35. The actual absorption rate from a meal can vary widely, from as low as 1% to as high as 40%, depending on dietary composition and individual iron status .
Enhancers and Inhibitors of Iron Absorption
- Enhancers: Ascorbic acid (vitamin C), muscle tissue (meat), and certain proteins can increase iron absorption.
- Inhibitors: Phytates (found in grains and legumes), polyphenols (in tea and coffee), and calcium can reduce absorption 345.
- Food preparation methods like cooking, fermentation, and germination can improve non-heme iron bioavailability by reducing inhibitors such as phytic acid .
Forms of Dietary Iron: Heme vs. Non-Heme
Iron in food exists as heme (from animal sources) and non-heme (from plant sources). Heme iron is absorbed more efficiently than non-heme iron. On average, humans consume 10–15 mg of dietary iron daily, but only 1–2 mg is absorbed, reflecting the low absorption efficiency, especially for non-heme iron 48.
Regulation of Iron Absorption: The Role of Hepcidin
Iron absorption is tightly regulated by the hormone hepcidin, produced by the liver. When iron stores are sufficient or high, hepcidin levels increase, reducing iron absorption. Conversely, low iron stores or increased need (such as during iron deficiency) lower hepcidin, allowing for greater absorption 910. Plasma hepcidin levels can explain a significant portion of the variation in iron absorption between individuals .
Impact of Iron Supplementation and Dosing
Oral iron supplements can acutely increase hepcidin, which in turn decreases iron absorption from subsequent doses. Higher single doses of iron result in lower fractional absorption, and taking iron more than once a day does not significantly increase total absorption. Lower, less frequent doses may maximize absorption efficiency .
Conclusion
The rate of iron absorption in the human body is generally low, averaging 8–10% in healthy adults, but can increase dramatically in states of deficiency. Absorption is influenced by dietary composition, the form of iron consumed, and individual physiological factors, especially iron status and hepcidin levels. Understanding these factors is crucial for optimizing dietary iron intake and addressing iron deficiency.
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