Iron Intake And Iron Absorption

Iron is one of the most abundant metals in the world, yet IDA continues to be one the most prominent nutritional disorders worldwide.1 Many factors contribute to this situation and they need to be understood to have a fuller appreciation of iron balance. Iron balance is regulated by several conditions: (a) the amount of iron ingested, (b) the amount of iron absorbed, (c) red blood cell formation using recycled and new iron, (d) iron stores, and (e) iron loss through blood loss or other sources (Fig. 5.1).

The amount of iron that needs to be obtained through the diet varies according to age and gender. Males need to absorb about 1 mg/day, premenopausal females about 0.2 to 2.0 mg/day, and children approximately 0.5 mg/day.2 For perspective, if an adult male eats a 2500-calorie diet, he will ingest about 15 mg of iron ofwhich only 10% will be absorbed, giving him 1.5 mg/day of iron that can be used for red cell production or stored in the reticuloendothelial system (RES).3 Iron in the diet is available as heme iron through meats or as nonheme/nonmeat iron. For a listing of sources, see

Table 5-1. For the infant, iron-fortified formulas and breast milk are major sources of iron. As the infant develops and rapidly gains weight, there is a high demand for iron. Most infants and young children will need some dietary supplementation to maintain iron balance (see Table 5.7).

Once iron is ingested, it is absorbed in the gastrointestinal (GI) tract and then transported into the circulation. The main portion of the GI tract involved is the duodenum and jejunum of the small intestine, where on average only about 10% of ingested iron is absorbed. This absorption rate is not static, however, and it decreases or increases relative to iron stores and the body's needs. Once absorbed, the iron molecule is converted from the Fe3+ (ferric) to the Fe2+ (ferrous) state by stomach acid, and then the iron molecules are transported through the circulation to the bone marrow via transferrin. Transferrin, the transport vehicle, is a plasma protein formed in the liver that assists iron delivery to the erythroblasts in the bone marrow. Transferrin receptors on the pronormoblast bind iron, so that iron molecules can immediately start being incorporated into the heme molecule during erythropoiesis. The willingness for the transferrin receptor to bind iron is influenced by the iron being delivered, the pH of the body, and, on the molecular level, the influence of an iron regulatory factor, ferritin repressor protein.4 An essential ingredient to seamless iron absorption and transport is a healthy GI tract. Procedures such a gastrectomy or gastric bypass, atrophic gastritis, or celiac disease may compromise iron absorption.5 There are dietary substances that enhance or diminish the absorption of iron from the diet (Tables 5.2 and 5.3), as well as foods with a high iron value (Table 5.4).

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