Iron deficiency anemia pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Physiology
- In the human body, iron is present in all cells and has several vital functions such as:
- A carrier of oxygen to the tissues from the lungs in the form of hemoglobin (Hb)
- Facilitator of oxygen use and storage in the muscles as myoglobin
- Transport medium for electrons within the cells in the form of cytochromes
- Integral part of enzyme reactions in various tissues.
- Total body iron averages approximately 3.8 g in men and 2.3 g in women.
Iron hemostasis (Absorption and bioavailability)
- There are several mechanisms that control human iron metabolism and safeguard against iron deficiency.
- Regulation of iron balance occurs mainly in the gastrointestinal tract through absorption.
- When the absorptive mechanism is operating normally, a person maintains functional iron and tends to establish iron stores.
- The percentage of iron absorbed (i.e., iron bioavailability) can vary from less than 1% to greater than 50%.
- The main factor controlling iron absorption is the amount of iron stored in the body.
- The gastrointestinal tract increases iron absorption when the body's iron stores are low and decreases absorption when stores are sufficient. An increased rate of red blood cell production can also stimulate iron uptake severalfold.
- Among adults, absorption of dietary iron averages approximately 6% for men and 13% for nonpregnant women in their childbearing years.
- The higher absorption efficiency of these women reflects primarily their lower iron stores as a result of menstruation and pregnancy.
- Among iron-deficient persons, iron absorption is also high. Absorption of iron increases during pregnancy, but the amount of the increase is not well defined; as iron stores increase postpartum, iron absorption decreases.
- The capacity of the body to absorb iron from the diet depends on the amount of iron in the body, the rate of red blood cell production, the amount and kind of iron in the diet, and the presence of absorption enhancers and inhibitors in the diet.
- Iron bioavailability also depends on dietary composition. Heme iron, which is found only in meat, poultry, and fish, is two to three times more absorbable than non-heme iron, which is found in plant-based foods and iron-fortified foods.
- The bioavailability of non-heme iron is strongly affected by the kind of other foods ingested at the same meal.
- Enhancers of iron absorption are heme iron (in meat, poultry, and fish) and vitamin C; inhibitors of iron absorption include polyphenols (in certain vegetables), tannins (in tea), phytates (in bran), and calcium (in dairy products).
- Vegetarian diets, by definition, are low in heme iron. However, iron bioavailability in a vegeterian diet can be increased by careful planning of meals to include other sources of iron and enhancers of iron absorption.
- In the diet of an infant, before the introduction of solid foods, the amount of iron absorbed depends on the amount and bioavailability of iron in breast milk or formula
External link
Center for disease control and prevention