Bioavailability of iron

Kies, C. (Ed.) "Nutritional Bioavailability of Iron", ACS SYMPOSIUM SERIES 203, American Chemical Society, Washington, D.C., 1982. 

Gastric acid and ascorbic acid facilitate the absorption of iron. Therefore, bioavailability of iron ingested with food is considerably decreased and also enteric-coated iron preparations are absorbed to a lesser extend. Fixed combinations with ascorbic acid increase the absorption of iron by at least 30%. However such increased uptake seems to have little advantage over a modest increase of dose. 

The recent enthusiasm for high fiber foods may carry a special challenge in considering food/drug toxicities. Vegetable fiber diets have been shown to reduce the toxicity of some drugs for animals (30). Presumably, phytates hold inorganic ions in a clathrate matrix that prevents absorption of the metal from the gut, other substances, e.g. bile acids, may also be bound (31). The bioavailability of iron as influenced by phytates in cereal foods via the formation of... 

Equation 17.26 is directly involved in DOM photomineralization, and Equation 17.25 yields Fe2+. Complexation of Fe(III) by organic ligands is in competition with the precipitation of ferric oxide colloids [79], and the formation of ferrous iron on photolysis of Fe(III)-carboxylate complexes is an important factor in defining the bioavailability of iron in aquatic systems. Iron bioavailabihty, minimal for the oxides and maximal for Fe2+, is considerably enhanced by the formation of Fe(III)-organic complexes and their subsequent photolysis. Iron bioavailabihty plays a key role in phytoplankton productivity in oceans [80-82], while that of freshwater is mainly controlled by nitrogen and phosphoms. 

Nutritional effects (bioavailability of iron, source of amino acids). 

Nutritional significance. As one of the major whey proteins in human milk and also relatively abundant in bovine colostrum, LF is of interest as a dietary source of amino acids as well as for the bioavailability of iron. LF has an... 

Miller, D. D., and Schricker, B. R. (1982). Nutritional bioavailability of iron. In ACS Symposium Series 23 (C. Kies, ed.). American Chemical Society, Washington, DC. 

The ability of any ligand (L) to outcompete hydroxide for Fe(III) is simply a function of the strength of the FemL complex and the pH and may be deduced from straightforward thermodynamic analysis [24,25]. As flagged in the Introduction however, Fe(III) complexes may form under nonequilibrium conditions in natural systems and be present for periods of time sufficient to influence the bioavailability of iron to aquatic organisms. This issue will be discussed further in Sect. 2.3. 

Kies, C. In Nutritional Bioavailability of Iron Kies, C., Ed. American Chemical Society Washington, DC, 1982, p. 183. 

Larsson, M., Minekus, M., and Havenaar, R. (1997), Estimation of the bioavailability of iron and phosphorus in cereals using a dynamic in vitro gastro-intestinal model, J. Sci. Food Agric., 74, 99-106. 

Achilles, K. M., Church, T. M., Wilhelm, S. W., Luther, G. W., and Hutchins, D. A. (2003). Bioavailability of iron to Trichodesmium colonies in the western subtropical Adantic Ocean. Umnol. 

Some trace-metal transport systems are even more complex than the one described in Figure 5 and involve the release of metallophores into the medium. The archetypes of these—and the only ones characterized so far—are the side-rophores produced by various species of marine bacteria to acquire iron. In the model organisms in which they have been characterized, the mechanisms of uptake are quite varied and complex, often involving intermediate siderophores in the peri-plasmic space and several transport proteins (Neilands, 1981). The effect of such siderophores on iron bioavailability is clearly not the same as that of EDTA. While complexation by a siderophore makes iron directly available to the bacteria which take up the complex (and whose rate of iron uptake is proportional to FeY), it drastically reduces the bioavailability of iron to most other organisms (whose rate of iron uptake is proportional to Fe ). For organisms which are able to promote the release of iron from the siderophore, e.g., by reduction of Fe(III), the effect of complexation is a less drastic decrease in iron... 

Smith K. R., Veranth J. M., Hu A. A., Eighty J. S., and Aust A. E. (2000) lnterleukin-8 levels in human lung epithelial cells are increased in response to coal fly ash and vary with the bioavailability of iron, as a function of particle size and source of coal. Chem. Res. Toxicol. 13, 118-125. 

The uptake of iron by the human intestine is governed not only by its dietary form and companion consituents, but also by the iron condition of the individual. Iron-depleted subjects absorb all forms of iron with greater avidity than do iron-replete individuals. In human dietetics, therefore, the ascorbic content of a diet can be included in the equation for describing the bioavailability of iron from a mixed diet (35). The interaction of iron nutrition and graded intakes of ascorbic acid (< 25 mg > 25 but < 75 mg and > 75 mg) as a prediction of iron availability from a mixed North American diet is plotted in Figure 1. 

The bioavailability of iron from any source (e.g., iron supplement, food or meal composite) is considered to be that portion of the total iron which is metabolizable. Philosophically, this concept is important because the amount of iron utilized by avian and mammalian species is directly associated with iron need. When assaying iron bioavailability, it is therefore necessary to use an organism whose need will exceed the amount provided. In animal assays of iron bioavailability, iron need is assured by a growth phase and/or creation of iron deficiency through feeding an iron deficient diet and phlebotomy. Because healthy subjects are usually used in human assays of iron bioavailability (Cook et al., 1981 Cook and Monson, 1976 Radhakrishman and Sivaprasad, 1980), it is inappropriate to compare the data obtained from animal and human assays. In fact it is questionable if assays of iron bioavailability yield good information on the quantities of metabolizable iron available when healthy human subjects are used. 

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