Iron absorption effects

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. 

The earlier discussion (7.3) leads one to expect absorption and enhancement effects in these high-temperature alloys. For example, the results for nickel will be very sensitive to the iron content. Nickel Ka has a wavelength about 0.1 A shorter than that of the iron K edge (Figure 7-2), and a slight increase in the iron content consequently means an increased absorption of nickel Ka, which tends to reduce the apparent nickel content (negative absorption effect). Furthermore, this increased absorption of nickel Ka will enhance iron Ka, whence an... 

Inspection of the table shows that the quotient a/Wj e is in fact nearly constant that I changes much less rapidly than W e] and that the critical depth has doubled when the highest oxide is reached. All three conditions are reflections of the (positive) absorption effect that occurs in this binary system when iron is replaced by oxygen, which has a lower mass absorption coefficient. 

Suppose one wishes nevertheless to use x-ray emission spectrography for the determination of iron in these materials. In principle, this can be done if the absorption effect is eliminated or kept constant—-if, for example, the material is placed in dilute solution in a relatively transparent solvent (7.8). 

Laby21 demonstrated in 1930, with a photographic plate as detector, that copper or iron in zinc could be detected in concentrations approaching 1 part per million by weight. To be sure, he used electron excitation so that absorption effects were minimized (7.10). By contrast, attempts made in the authors laboratory to estimate alkaline-earth metals in brines were unsuccessful, primarily because of the high absorption effects that accompanied x-ray excitation. The use of dilution with a relatively transparent solvent can sometimes reduce or eliminate absorption effects (7.8), but this procedure will fail if the element to be determined is present at too low a concentration in the presence of another substance (the salt in brine in the example cited) primarily responsible for the absorption effect. A case in which dilution is helpful in connection with the absorption effect of the. element sought is that of tetraethyllead fluid in gasoline (7.13). 

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. 

Thus, in our investigations, the sulfuric acid used in hydrolysate production has been replaced by phosphoric acid. Such a change should be effective in diminishing the iron absorption, as the iron phosphates are not... 

Results from some recent studies (19-36) on the effects of fiber are summarized in Table I. For the most part, the results are from multi-day balance studies. However, Turnland et al. (36) used the stable isotope fecal monitoring method to assess zinc utilization and Simpson et al. (24) measured iron absorption from a single test meal. 

In a series of studies, Cook and co-workers (48,49,50) observed a marked decrease in non-heme iron absorption when soy protein was added to beef or protein mixtures or when soy protein was consumed as the primary protein source in test meals and compared to the effects of including egg albumen or beef alone in the test meal (Table III) Hallberg and Rossander (38J, however, found less of an effect when total iron absorption (heme plus non-heme iron) was considered. Likewise, in a study in which reconstituted textured soy was used to replace 30% of the beef, the absorptions of total iron were not greatly altered (51). In a study by Stekel et al. (52), replacing part of the beef with soy isolate or adding hydrated isolate to beef decreased non-heme iron absorption from 12.4% to 9.2 and 9.3%, respectively. In a related study, non-heme and total iron absorptions were low when soy isolate was the major protein source. 

Lynch et al. (5 7) found non-heme iron absorptions, as measured by single test meals, for black beans, lentils, mung beans split peas, and whole soybeans to be low (0.84 to 1.91%). This suggests that many commonly consumed legumes are poor sources of iron whether legumes other than soy may have an "offsetting" enhancing effect on heme-iron absorption cannot be predicted. 

Cook, J. D., and Monsen, E. R. (1976). Food iron absorption in man 11. The effect of EDTA on absorption of dietary non-heme iron. Am. ]. Clin. Nutr. 29, 614-620. 

Deehr, M. S., Dallal, G. E., Smith, K. T., Taulbee, J. D., and Dawson-Hughes, B. (1990). Effects of different calcium sources on iron absorption in postmenopausal women. Am.. Clin. Nutr. 51, 95-99. 

A numerical matrix correction technique is used to linearise fluorescent X-ray intensities from plant material in order to permit quantitation of the measurable trace elements. Percentage accuracies achieved on a standard sample were 13% for sulfur and phosphorus and better than 10% for heavier elements. The calculation employs all of the elemental X-ray intensities from the sample, relative X-ray production probabilities of the elements determined from thin film standards, elemental X-ray attenuation coefficients, and the areal density of the sample cm2. The mathematical treatment accounts for the matrix absorption effects of pure cellulose and deviations in the matrix effect caused by the measured elements. Ten elements are typically calculated simultaneously phosphorus, sulfur, chlorine, potassium, calcium, manganese, iron, copper, zinc and bromine. Detection limits obtained using a rhodium X-ray tube and an energy-dispersive X-ray fluorescence spectrometer are in the low ppm range for the elements manganese to strontium. 

Sun, Y. and Pignatello, J.J. (1993) Photochemical reactions involved in the total mineralization of 2,4-D by iron(3+)/hydrogen peroxide/UV. Environ. Sci. Technol. 27, 304-310 Toepfer, B., Gora, A. and Li Puma, G. (2006) Photocatalytic oxidation of multicomponent solutions of herbicides Reaction kinetics analysis with explicit photon absorption effects. Appl. Catal. B Environ. 68,171-180... 

Modified-release preparations release iron gradually so less iron is present in the gastrointestinal tract at any one time. However, because they are modified-release, these preparations are likely to carry the iron past the first part of the duodenum into an area of the gut where iron absorption may be poor. The low incidence of side-effects may reflect the small amounts of iron available for absorption under these conditions and so the preparations have no therapeutic advantage and should not be used. 

There are several inherited diseases which are associated with the gradual excess accumulation of iron via the gut. Hereditary haemochromatosis is a relatively rare condition in which iron absorption is increased through an unidentified mechanism. This condition usually presents in the fourth or fifth decade of life with the secondary effects of iron overload such as heart failure, liver cirrhosis or sugar diabetes. As the production of red cells is unaffected, the excess iron can be removed slowly by venesecting a unit of blood every week for up to two years. However, in the acute situation, iron chelation may be used to remove toxic low-molecular-weight iron until sufficient negative iron balance has been obtained by venesection. 

Iron absorption may also be increased secondary to chronic haemolysis as in patients with thalassaemia intermedia. In this group of patients, the anaemia is not usually sufficiently severe to necessitate regular blood transfusions as in thalassaemia major, but iron accumulates over many years from increased absorption via the gut. However, unlike haemochromatosis, venesection is not a therapeutic option, and iron chelation is the only effective way to remove the excess iron. 

The non-toxic 3-hydroxypyrones (Structure 12) bind iron(III) forming water-soluble complexes [44], In the pH range 4-7, they possess a lower affinity for iron(III) than EDTA, and by virtue of the kinetic lability of such complexes, are able to donate iron to high-affinity binding sites, while minimizing non-selective binding to foodstuffs. Thus, iron presented as a maltol complex is relatively well absorbed [103,104], In contrast, the presence of EDTA reduces iron absorption by the intestine. Ferric maltol is the only simple iron(III) preparation which compares favourably with iron(II) sulphate [105], and in contrast to iron(II) sulphate, there are few, if any, side effects associated with the oral administration of ferric maltol. Consequently, patient compliance is likely to be superior with this iron preparation. 

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