Iron, absorption

Iron Absorption. A very important effect of ascorbic acid is the enhancement of absorption of nonheme iron from foods. Ascorbic acid also enhances the reduction of ferric iron to ferrous iron. This is important both in increasing iron absorption and in its function in many hydroxylation reactions (140,141). In addition, ascorbic acid is involved in iron metaboHsm. It serves to transfer iron to the Hver and to incorporate it into ferritin. 

Results of analyses of raw and cooked foods demonstrate that the greatest change appears to be related to iron absorption from the iron cooking pot. 

Iron Absorption Is Limited Strictly Controlled but Is Enhanced by Vitamin C Ethanol... 

Inorganic iron is absorbed only in the (reduced) state, and for that reason the presence of reducing agents will enhance absorption. The most effective compound is vitamin C, and while intakes of 40-60 mg of vitamin C per day are more than adequate to meet requirements, an intake of 25-50 mg per meal will enhance iron absorption, especially when iron salts are used to treat iron deficiency anemia. Ethanol and fructose also enhance iron absorption. Heme iron from meat is absorbed separately and is considerably more available than inorganic iron. However, the absorption of both inorganic and heme iron is impaired by calcium—a glass of milk with a meal significantly reduces availabiUty. 

Overall regulation of iron absorption is complex and not well understood mechanistically. It occurs at... 

HFE has been shown to be located in cells in the crypts of the small intestine, the site of iron absorption. There is evidence that it associates with P2 niicroglobu-lin, an association that may be necessary for its stability, intracellular processing, and cell surface expression. The complex interacts with the transferrin receptor (TfR) how this leads to excessive storage of iron when HFE is altered by mutation is under close smdy. The mouse homolog of HFE has been knocked out, resulting in a potentially useful animal model of hemochromatosis. 

Iron is, as part of several proteins, such as hemoglobin, essential for vertebrates. The element is not available as ion but mostly as the protein ligands transferrin (transport), lactoferrin (milk), and ferritin (storage), and cytochromes (electron transport) (Alexander 1994). Toxicity due to excessive iron absorption caused by genetic abnormalities exists. For the determination of serum Fe a spectrophoto-metric reference procedure exists. Urine Fe can be determined by graphite furnace (GF)-AAS, and tissue iron by GF-AAS and SS-AAS (Alexander 1994 Herber 1994a). Total Iron Binding Capacity is determined by fuUy saturated transferrin with Fe(III), but is nowadays mostly replaced by immunochemical determination of transferrin and ferritin. 

Bouhallab, S., Cinga, V., Ait-Oukhatar, N., Bureau, F., Neuville, D., Arhan, P., Maubois, J. L., and Bougie, D. (2002). Influence of various phosphopeptides of caseins on iron absorption. J. Agric. Food Chem. 50, 7127-7130. 

Hereditary hemochromatosis is an autosomal recessive disease of increased intestinal iron absorption and deposition in hepatic, cardiac, and pancreatic tissue. Hepatic iron overload results in the development of fibrosis, hepatic scarring, cirrhosis, and hepatocellular carcinoma. Hemochromatosis can also be caused by repeated blood transfusions, but this mechanism rarely leads to cirrhosis. 

Dosing for iron should be divided equally into two to three doses daily. An empty stomach (1 hour before or 2 hours after a meal) is preferred for maximal absorption. After absorption, iron binds to transferrin in the plasma and is transported to the muscles (for myoglobin), liver (for storage), or bone marrow (for red cell production). Iron is not actively excreted from the body but is lost through other measures already described.7 Some studies suggest that iron absorption may be... 

Figure 4.1 (a) Mechanism of iron absorption of Strategy I in the roots of dicots and non-graminaceous monocots, (b) Mechanism of iron absorption of Strategy II in the roots of graminaceous plants. Reprinted from Mori, 1998, by courtesy of Marcel Dekker, Inc. 

O Iron Absorption in Mammals with Particular Reference to Man... 

Inhibitors of non-haem iron absorption include polyphenols and phytates. The former, secondary plant metabolites rich in phenolic hydroxyl groups, are found... 

Figure 8.2 Rat duodenal cells divide in the crypts of Lieberktihn and differentiate while migrating to the villus tips within approximately 48 h. The crypt cells take up iron from the blood, and are thereby able to sense the body s state of iron repletion. They migrate to the villus tips where this information determines their iron absorption capacity from the intestinal lumen. Adapted from Schumann et al., 1999, by permission of Blackwell Science.

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