Fractional Iron Absorption Research Articles

Effect of Ascorbic Acid and Particle Size on Iron Absorption from Ferric Pyrophosphate in Adult Women

The effects of added ascorbic acid and particle size on iron absorption from ferric pyrophosphate were evaluated in adult women (9-10 women/study) based on erythrocyte incorporation of iron stable isotopes (57Fe or 58Fe) 14 days after administration. Three separate studies were made with test meals of iron-fortified infant cereal (5 mg iron/meal) and the results are presented as geometric means and relative bioavailability values (RBV, FeSO4 = 100%). The results of study 1 showed that iron absorption was significantly lower from ferric pyrophosphate (mean particle size 8.5 microm) than from FeSO4 in meals without ascorbic acid (0.9 vs. 2.6%, p < 0.0001, RBV 36%) and in the same meals with ascorbic acid added at a 4:1 molar ratio relative to fortification iron (2.3 vs. 9.7%, p < 0.0001, RBV 23%). Ascorbic acid increased iron absorption from ferric pyrophosphate slightly less (2.6-fold) than from FeSO4 (3.7-fold) (p < 0.05). In studies 2 and 3, RBV of ferric pyrophosphate with an average particle size of 6.7 microm and 12.5 pm was not significantly different at 52 and 42% (p > 0.05), respectively. In conclusion, the addition of ascorbic acid increased fractional iron absorption from ferric pyrophosphate significantly, but to a lesser extent than from FeSO4. Decreasing the mean particle size to 6.7 microm did not significantly increase iron absorption from ferric pyrophosphate.

Iron absorption in breast-fed infants: effects of age, iron status, iron supplements, and complementary foods , ,

Iron supplements are often recommended for older breast-fed infants, but little is known about factors affecting iron absorption from human milk or supplements. We investigated the effects of age, iron status, and iron intake on iron absorption in healthy, term, breast-fed infants. Twenty-five infants were randomly assigned to receive either 1) iron supplements (1 mg x kg(-1) x d(-1)) from 4 to 9 mo of age, 2) placebo from 4 to 6 mo and iron supplements from 6 to 9 mo, or 3) placebo from 4 to 9 mo. Infants were exclusively breast-fed to 6 mo and partially breast-fed to 9 mo of age. Iron absorption was assessed by giving (58)Fe with mother's milk at 6 and 9 mo. Blood samples were obtained at 4, 6, and 9 mo, and complementary food intake was recorded at 9 mo. At 6 mo, mean (+/-SD) fractional iron absorption from human milk was relatively low (16.4 +/- 11.4%), with no significant difference between iron-supplemented and unsupplemented infants. At 9 mo, iron absorption from human milk remained low in iron-supplemented infants (16.9 +/- 9.3%) but was higher (P = 0.01) in unsupplemented infants (36.7 +/- 18.9%). Unexpectedly, iron absorption at 9 mo was not correlated with iron status but was significantly correlated with intake of dietary iron, including supplemental iron. Changes in the regulation of iron absorption between 6 and 9 mo enhance the infant's ability to adapt to a low-iron diet and provide a mechanism by which some, but not all, infants avoid iron deficiency despite low iron intakes in late infancy.

Iron metabolism and requirements in early childhood: do we know enough?: a commentary by the ESPGHAN Committee on Nutrition.

*University of Lancashire, Lancashire, United Kingdom; †University of Milano, Milano, Italy; ‡University of Lund, Malmo, Sweden; §Hopital des Enfants Malades, Paris, France; Hopital Necker Enfants-Malades, Paris, France, ¶Umea University, Umea, Sweden; #University of Munich, Munich, Germany; **Free University of Amsterdam, Amsterdam, The Netherlands; ††Royal Veterinary and Agricultural University, Frederiksberg, Denmark; ‡‡CHUV University Hospital, Lausanne, Switzerland; §§University of Liege, Liege, Belgium; Medical University of Warsaw, Warsaw, Poland; and ¶¶University of Glasgow, Glasgow, United Kingdom

Absorption of iron from unmodified maize and genetically altered, low-phytate maize fortified with ferrous sulfate or sodium iron EDTA

Reducing the phytate content in grains by genetic manipulation is a novel approach to increasing nonheme-iron absorption from mixed diets. Fractional iron absorption from a genetically modified strain of low-phytate maize (LPM) increased significantly, by 50%. We assessed iron absorption from porridges prepared from the same LPM (lpa-1-1 mutant) and unmodified wild-type maize (WTM), both of which were fortified with either ferrous sulfate or sodium iron EDTA. Porridges providing 3.4 mg Fe were fortified with either ferrous sulfate or sodium iron EDTA to provide an additional 1 mg Fe/serving. In 14 nonanemic women, iron absorption was measured as the amount of radioiron incorporated into red blood cells (extrinsic tag method) 12 d after consumption of the study diets. No significant effect of phytate content on iron absorption was found when porridge was fortified with either sodium iron EDTA or ferrous sulfate. Fractional absorption of iron from WTM porridge fortified with sodium iron EDTA (5.73%) was 3.39 times greater than that from the same porridge fortified with ferrous sulfate (1.69%). Fractional absorption of iron from the sodium iron EDTA-fortified LPM porridge (5.40%) was 2.82 times greater than that from LPM porridge fortified with ferrous sulfate (1.91%) (P<0.0001 for both comparisons, repeated-measures analysis of variance). Thus, the previously identified benefit of LPM was no longer detectable when maize porridge was fortified with additional iron. Iron was absorbed more efficiently when the fortificant was sodium iron EDTA rather than ferrous sulfate, regardless of the type of maize.

Low-phytic-acid Grains

As one approach to the improvement of the nutritional quality of crops for both foods and feeds, low-phytic-acid (lpa) mutants of maize and other cereals have been isolated. An important advantage of lpa mutants is that the bioavailability of a range of minerals may be improved, although phytic acid can also function as an antioxidant. Livestock producers are primarily concerned with excretion of feed phytic acid phosphorus by livestock and fish. This contributes to water pollution and is a major environmental issue in developed countries. In these mutants, phytic acid phosphorus is reduced by 55% to 66%, which is matched by an equal increase in inorganic phosphorus. Greater reductions in phytic acid, as high as 95% to 99%, may be desirable and are possible. The first two studies of an lpa maize in human nutrition found increased fractional absorption of iron and zinc in the lpa maize as compared with the control maize. Yields of the best lpa lines, first developed in the mid-1990s, now range between 5% and 15% below those of the highest-yielding commercial varieties. Because of benefits for animal nutrition, lpa crops could become highly profitable for use as animal feeds. All lpa lines to date have been developed using classical genetic methods; these classically obtained mutants affect the expression of a given gene throughout the tissues and organs of a plant. BY using a biotechnology approach, it may be possible to achieve optimal levels of phytic acid reduction and target the desired effect to the seed, thereby reducing any undesirable agronomic effects of whole-plant mutants.

Stable isotope labels as a tool to determine the iron absorption by Peruvian school children from a breakfast meal

Fractional iron absorption from a breakfast meal was determined in Peruvian children employing stable iron isotopes as labels. Iron isotopic analysis was performed by the recently developed negative thermal ionization technique for high-precision iron isotope ratio measurements using FeF4– ions. By increasing the ascorbic acid content of the standard breakfast meal as served within the Peruvian school-breakfast program from 27 mg to 70 mg, it was possible to increase the geometric mean fractional iron absorption significantly from 5.1% (range 1.6–13.5%) to 8.2% (range 3.1–25.8%). Fractional iron absorption was calculated according to isotope dilution principles and by considering the non-monoisotopic character of the used spikes.

Bioavailability in Man of Iron in Human Milk and Cow's Milk in Relation to Their Calcium Contents

Iron absorption from human milk and cow's milk was compared in the same subjects using two radio-iron tracers and extrinsic labeling of the iron. Previously observed higher iron absorption from human milk was confirmed as 19.5 +/- 17.3% (mean +/- SD) in cow's milk versus 48.0 +/- 25.5% in human milk; mean individual absorption ratio was 0.39 +/- 0.18 (p less than 0.0001). Cow's milk has a several times higher content of calcium, recently established to be a potent inhibitor of iron absorption. Adding calcium chloride to human milk in amounts to equate the calcium content of cow's milk significantly reduced iron absorption [39.1 +/- 17.8% (mean +/- SD) versus 21.3 +/- 10.6%]; mean individual absorption ratio with or without added calcium was 0.58 +/- 0.12 (mean +/- SD) (p less than 0.0001). Differences in calcium content could explain at least 70% of the difference in iron bioavailability between milks. It is suggested that the remaining 30% difference may mainly be an artifact related to inhomogeneous radioiron-labeling of milk iron compounds, especially in human milk, and that the main difference in true iron absorption between human and cow's milk is related to their different calcium contents. The rather high fractional iron absorption from human milk can be explained by its low iron content. There is nothing to indicate that human milk contains any enhancer of iron absorption. The marked inhibiting effect of calcium on iron absorption should be considered in the design of infant formulas to achieve an optimal balance in the contents of calcium and iron.

Iron Absorption from Bread in Humans: Inhibiting Effects of Cereal Fiber, Phytate and Inositol Phosphates with Different Numbers of Phosphate Groups

Iron absorption was measured from five kinds of bread made from various types of flour and fermented in different ways in order to obtain a wide variation in the content of fiber, phytate (inositol hexaphosphate) and its degradation products, inorganic phosphate and inositol phosphates with fewer numbers of phosphate groups (inositol pentaphosphate through monophosphate). Each experiment had 9–10 subjects and, in each subject, iron absorption was measured from control rolls made from low extraction wheat flour and one kind of test roll using two different radioiron tracers: 55Fe and 59Fe. The inhibition of iron absorption was closely related to the content of phytate-phosphorous as determined using the AOAC method, and to the sum of the tri- through hexaphosphate groups as determined using the HPLC method. As an example, prolonged fermentation of whole-rye bread reduced total inositol phosphates to the same amount as in the control rolls and increased fractional iron absorption to the same high level, in spite of a fiber content five times as great. The results strongly suggest that the inhibitory effect of bran on iron absorption is due to its content of phytate and other inositol phosphates present after fermentation, rather than to its content of fiber or other constituents. Thus, effective fermentation will increase the bioavailability of iron in whole-meal bread.

Competitive inhibition of iron absorption by manganese and zinc in humans

Zinc and manganese may interfere with iron absorption because of similar physicochemical properties and shared absorptive pathways. The effects of zinc and manganese on iron absorption were studied in human subjects by using paired observations and a dual-radioisotope method (55Fe and 49Fe). Manganese inhibited iron absorption both in solutions and in a hamburger meal. Fractional iron absorption is strongly dose dependent. Adding 2.99 mg Mn to 0.01 mg Fe reduced iron absorption to the same extent as increasing the iron dose 300-fold to 3 mg, strongly indicating a direct competitive inhibition of manganese on iron absorption. In the same experiment with zinc, no inhibitory effect was observed, suggesting different pathways for the absorption of zinc and iron. An intraluminal interaction may occur, because a fivefold excess of zinc to iron (15 mgZn/3 mg Fe) reduced iron absorption by 56% when given in a water solution but not when given with a hamburger meal.

Ferrokinetic studies with stable isotopes as tracers.

A methodology for ferrokinetic studies based on the administration of iron stable isotopes was developed. Fractional plasma clearance and intestinal iron absorption in rabbits were determined using the double tracer technique. Three rabbits were given 58Fe solution intravenously and about 40 min later 57Fe solution orally. Blood samples were drawn at different times following administration. The analysis of the single iron isotopes content in plasma samples was made by proton nuclear activation. The results were compared with those obtained from the administration, to the same rabbits, of the radioactive isotopes 55Fe and 59Fe. The agreement was found to be satisfactory.

Evidence and mechanism for pectin-reduced intestinal inorganic iron absorption in idiopathic hemochromatosis

The intestinal absorption of iron was measured in 13 patients suffering from idiopathic hemochromatosis by using a double radiotracer technique. For each patient, iron absorption was determined in the fasting state, i.e., under basal conditions, and after an oral indigestible fiber load (9 g/m2 of body surface) with either pectin (group I: eight patients) or cellulose (group II: five patients). The results were compared with those from a group of seven normal control subjects investigated under basal conditions. The patients with haemochromatosis (groups I and II) had a significant increase in the basal value of fractional iron absorption as compared with controls. In the patients of group I, the pectin induced a significant fall in fractional iron absorption (P less than 0.02). In group II, iron absorption rates remained unchanged whether or not cellulose was given. Furthermore, we found in vitro that pectin had a high iron binding activity, while cellulose bound none. From the present study, we conclude that pectin but not cellulose reduces iron absorption by forming unabsorbable complexes with dietary iron. Thus, enrichment of the diet with foods providing significant amounts of noncellulosic dietary fibers, such as pectin, may be useful in the management of hemochromatosis patients.