Synthesis, characterization, and bioavailability in rats of ferric phosphate nanoparticles

Particle size is a determinant of iron (Fe) absorption from poorly soluble Fe compounds. Decreasing the particle size of metallic Fe and ferric pyrophosphate added to foods increases Fe absorption. The aim of this study was to develop and characterize nanoparticles of FePO(4) and determine their bioavailability and potential toxicity in rats. Amorphous FePO(4) nanopowders with spherical structure were synthesized by flame spray pyrolysis (FSP). The nanopowders were characterized and compared with commercially available FePO(4) and FeSO(4), including measurements of specific surface area (SSA), structure by transmission electron microscopy, in vitro solubility at pH 1 and 2, and relative bioavailability value (RBV) to FeSO(4) in rats using the hemoglobin repletion method. In the latter, the potential toxicity after Fe repletion was assessed by histological examination and measurement of thiobarbituric acid reactive substances (TBARS). The commercial FePO(4) and the 2 FePO(4) produced by FSP (mean particle sizes, 30.5 and 10.7 nm) had the following characteristics: SSA: 32.6, 68.6, 194.7 m(2)/g; in vitro solubility after 30 min at pH 1: 73, 79, and 85% of FeSO(4); and RBV: 61, 70, and 96%, respectively. In the histological examinations and TBARS analysis, there were no indications of toxicity. In conclusion, nanoparticles of FePO(4) have a solubility and RBV not significantly different from FeSO(4). Reducing poorly soluble Fe compounds to nanoscale may increase their value for human nutrition.     

A comparison of physical properties, screening procedures and a human efficacy trial for predicting the bioavailability of commercial elemental iron powders used for food fortification

Elemental iron powders are widely used to fortify staple foods. Experimental evidence indicates that there is considerable variation in the bioavailability of different products. For some powders, it may be too low to permit a significant impact on iron status. This study was designed to evaluate possible approaches to screening commercial iron powders for predicted bioavailability, to identify products that have the potential to improve iron status, and to ascertain whether bioavailability is related to the method of manufacture. Nine commercial iron powders were allocated to one of five types based on the production process; carbonyl, electrolytic, hydrogen-reduced (H-reduced), carbon monoxide-reduced (CO-reduced), and other reduced. Structure by scanning electron microscopy and physical properties (pycnometric and apparent density, particle size distribution, Fisher subsieve size, and surface area) were determined on all samples. Selected samples (one or more of each type depending on the cost of the assay) were then subjected to five screening procedures that have previously been advocated for predicting bioavailability in humans--issolution rate in 0.1 mol/L HCl, dialyzability and Caco-2 cell iron uptake, both after simulated in vitro gastrointestinal digestion, relative bioavailability (RBV) with respect to ferrous sulfate by the AOAC rat hemoglobin repletion method, and plasma iron tolerance tests in human volunteers. The results for particle size distribution, surface area, Fisher subsieve size, dissolution rate in 0.1 mol/L HCl, and RBV in rats were significantly correlated and consistent for powders of the same type. However, values for different powder types were significantly different. There was no correlation between either dialyzability or Caco-2 cell uptake and the predicted bioavailability estimates based on the physical properties, dissolution rates, RBV in rats, or human efficacy data. Although human plasma iron tolerance tests were in general agreement with the other measures of predicted bioavailability, they did not provide information that would have improved the precision of bioavailability estimates based on physical properties, dissolution in HCl and/or RBV in rats. Our observations indicate that the dissolution rate in 0.1 mol/L HCI under standardized conditions is highly predictive of potential bioavailability and that it would be the most practical approach to developing a reliable and sensitive screening procedure for predicting and monitoring the bioavailability of commercial elemental iron powder products. Some, but not all, of the carbonyl and electrolytic iron powders had the highest predicted bioavailability values. The predicted bioavailability for the reduced iron products was lower and variable, with the lowest values being recorded for the carbon monoxide and other reduced iron products. Two powder types were selected for a human efficacy trial, electrolytic (because it is the iron powder type recommended by WHO) and hydrogen-reduced (because of its widespread use). Electrolytic/A131 and H-reduced/AC-325 had relative efficacies compared with ferrous sulfate monohydrate of 77% and 49%, respectively, based on the change in body iron stores in Thai women with low iron stores, who received an additional 12 mg iron per day, six days per week for 35 weeks in wheat-based snacks. We conclude that there is significant variability in the bioavailability of the commercial iron powders that we evaluated (those used for food fortification at the time that our studies were initiated), and that bioavailability is related in part to production method. The bioavailability of some carbonyl and electrolytic iron powders may be adequate for effective food fortification. The reduced iron powders that we tested are unlikely to have an adequate impact on iron nutrition at the fortification levels currently employed, although preliminary analysis of a new H-reduced product indicates that it may be possible to improve the bioavailability of individual powders of this type of product. We did find significant differences among products in both the electrolytic and carbonyl categories. Therefore, all products should be screened rigorously.     

Biological availability of iron supplements for rats, chicks and humans.

Fourteen experiments were concluded on the effect of protein and carbohydrate sources in the assay diets on the relative biological values (RBV) of food grade sodium iron pyrophosphate (NaFePP) and ferric orthophosphate (FePO4) vs. ferrous sulfate (FeSO4) for rats and chicks, using the response in blood hemoglobin to graded levels of supplemental iron as the assay criterion. Two trials were made with volunteers to estimate the RBV of NaFePP and FePO4 for humans, based on the increase in plasma iron 2 hours after ingestion of 100 mg of iron of a test dose following an overnight fast. The RBV of iron from NaFePP and FePO4 for rats were consistently lower when the basal diet contained nonfat dried milk (9 to 16 and 28, respectively, vs. FeSO4=100) than when casein was used (25 to 28 and 49, respectively). The addition of 22% beta-lactose, replacing sucrose in a diet containing casein fed to rats, significantly reduced the RBV of iron from NaFePP from 25 to 15; the addition of 22% alpha-lactose or 40% glucose in place of sucrose had no effect on the RBV of this iron source. The RBV of iron from NaFePP and FePO4 for chicks were 4 to 6 and 4, respectively, with the source of dietary protein having no effect. Very low RBV of iron from NaFePP and FePO4 (4.3 and 5.9, respectively, vs. FeSO4=100) were also obtained with human subjects.     

The relative bioavailability in humans of elemental iron powders for use in food fortification

Summary Background Bioavailability data in humans of elemental iron powders is limited although elemental iron is a common form of iron when used as a fortificant. Aim of the study The relative bioavailability (RBV) of seven elemental iron powders, five commercially available and two developmental are evaluated. In addition, one commercial electrolytic iron powder given with ascorbic acid (AA) was examined. Methods Based on a validated method this double–blinded randomized crossover study included three groups of male blood donors (n = 3*16) who were served rolls fortified with different elemental iron powders or ferrous sulfate (FeSO₄) nine weeks apart. Blood samples were drawn every hour for six hours. RBV was obtained by comparing the increase in serum iron concentration induced by the elemental iron with the increase induced by FeSO₄. Results All elemental iron powders studied were significantly less well absorbed compared to FeSO₄. The electrolytic iron given with 50–mg AA was as well absorbed as FeSO₄ (molar ratio = 1:6, AA:Fe). The mean RBVs of the iron powders were: electrolytic (A–131, RBV = 0.65); electrolytic (Electrolytic, RBV = 0.59); carbonyl (Ferronyl, RBV = 0.58); H–reduced (AC– 325, RBV = 0.56); H–reduced (Hi–Sol, RBV = 0.50); carbonyl (CF, RBV = 0.37); reduced (Atomet 95SP, RBV = 0.36). The reduced iron was distinguished by having significantly lower RBV (0.36) although no significant overall ranking was possible. Conclusion Based on a validated method this doubleblinded cross–over study in humans showed that the evaluated elemental iron powders currently available for commercial use are significantly less well absorbed compared to FeSO₄. The results indicate that the reduced iron powder was absorbed to a lower extent compared to the other iron powders and only 36% compared to FeSO₄. Ascorbic acid seems to improve the bioavailability of elemental iron even though a rather low molar ratio is used. Thus, if confirmed, this enhancing effect of ascorbic acid on elemental iron when used as a fortificant could be used by co–fortifying them.     

The relative bioavailability of plant and animal sources of iron to the cat and chick

The biological availability of iron (Fe) from corn gluten meal (CGM) and dried beef liver (DBL), to represent plant and animal sources of Fe, respectively, was determined by hemoglobin depletion-repletion bioassays with young cats and chicks. Animals were rendered anemic by feeding a low-Fe, casein-dextrose diet (5 mg Fe/kg diet) for 28 (cats) or 7 (chicks) days. Repletion diets, supplemented with reagent grade FeSO₄·7H₂O at graded increments below the animal's requirement, were fed to cats for 28 days. A regression equation relating final hemoglobin concentration to supplemental Fe intake was computed and relative bioavailability estimates made using the standard curve technique. Anemic chicks were fed graded levels of Fe supplied by ferrous sulfate or one of the test sources of Fe for 14 days and a multiple linear regression equation was calculated. The percent bioavailable Fe was then estimated by slope ratio analysis. Estimated relative bioavailability to the kitten of the Fe supplied by CGM was 20%; an estimate of 347% was obtained for DBL. For the chick, relative Fe bioavailabilities of 84 and 90% were estimated for CGM and DBL, respectively. Thus the cat appeared to be unique in its ability to utilize Fe from DBL approximately three times more efficiently than ferrous sulfate and ten times more efficiently than Fe from CGM.     

Influence of fish on the bioavailability of plant iron in the anemic rat

The effect of fish protein and fish oil on the utilization of endogenous iron in wheat bran, spinach and soy protein isolate was investigated by using the anemic rat as an animal model. Marine products were substituted for casein and corn oil in the diets of these animals. Hemoglobin regeneration was one criteria used to measure iron uptake. Relative biological values (RBV) were computed from a regression equation obtained from control animals receiving graded levels of FeSO4 X 7H2O. The RBV of iron from plant sources provided in diets containing casein-corn oil versus fish-fish oil were: wheat bran, 123 vs. 111%; spinach, 53 vs. 49%; and soybean isolate, 84 vs. 67%; RBV FeSO4 = 100%. These changes were not significant. The decreases in iron absorption from diets containing marine products was attributed to the fish oil. Absorption of exogenous iron (59Fe) was measured in the same animals after the 14-day repletion period. Assimilation of the 59Fe was highly correlated (r2 = 0.958) with hemoglobin level at time of dosing. Diet composition did not appear to have the same effect on the percentage of 59Fe retained after 110 hours by the rat as compared to levels of hemoglobin regeneration (i.e., RBV). A "meat factor" effect was not shown by substituting fish for casein the diets containing plant iron sources fed anemic rats.     

Relative bioavailability of iron in carbonyl iron and complex ferric orthophosphate to rat.

The relative biological availability (RBV of FeSO4.7H2O = 100%) of carbonyl iron and complex ferric orthophosphate in flour and bread baked with this flour was determined in a rat hemoglobin repletion assay. Hemoglobin iron gain and iron intake during repletion were used as dose-response parameters, and the relative biological values were assessed by the slope-ratio method. The RBV of carbonyl iron in flour was not calculated because the statistical validity of the slope-ratio method was not fulfilled. The RBVs of all the tested iron sources were significantly lower than that of the ferrous sulphate standard (p less than 0.01). The RBV for complex ferric orthophosphate in flour was 45 +/- 8%, and for complex ferric orthophosphate and carbonyl iron in bread 36 +/- 7% and 35 +/- 7%, respectively. There were no differences in the bioavailability of carbonyl iron and complex ferric orthophosphate (p greater than 0.01). Baking did not effect the bioavailability of complex ferric orthophosphate (p greater than 0.01).     

The lack of effect of added dibasic calcium phosphate on the bioavailability of electrolytic iron in infant cereals

Infant cereals are generally fortified with about 1.0% Ca, 0.8% P and 0.03% Fe. The effect of such high levels of added Ca and P on the bioavailability of iron is not known. The purpose of this investigation was, therefore, to determine the effect of adding 0.25, 0.50 and 1.00% Ca as CaHPO₄.2H₂O to iron-fortified (0.03% added as electrolytic iron) rice cereal on the 2-week hemoglobin regeneration in iron-depleted male Sprague-Dawley rats. The mixed cereal with banana was also tested but only at the normal level of Ca and P. The cereals provided 30 or 60 mg Fe/kg diet. From the initial and final body weights, 2-week food intake and hemoglobin levels it was concluded that there was no significant effect of the Ca-P addition on the bioavailability of iron.     

Iron availability of a fortified processed wheat cereal: a comparison of fourteen iron forms using an in vitro digestion/human colonic adenocarcinoma (CaCo-2) cell model

In this three-phase study we first compared the availability of fourteen Fe forms in a wheat-based ready-to-eat breakfast cereal using an in vitro digestion/human colonic adenocarcinoma (CaCo-2) cell model. We then investigated the effect of milk and/or coffee on those fortified cereals found in phase 1 to show promising increases in Fe availability. The Fe forms assessed in phase 1 were reduced (control), carbonyl, electrolytic, FePO(4), FeSO(4), FeCO(3), Na(2)FeEDTA, Ferrochel (Albion Laboratories, Clearfield, UT, USA; ferrous bis-glycinate), encapsulated ferrous fumarate, FeSO(4), ferrous lactate and Biofer (LipoTech, Britwell Salome, Oxfordshire; FeSO(4)), SQM (Sea-Questra-Min Iron; Quali Tech, Chaska, MN, USA; polysaccharide-complexed FeSO(4)) and Sun Active (Taiyo Kagaku, Yokkaichi, Japan). All these forms increased Fe uptake compared with the unfortified cereal. Relative to the control, the following increases in Fe availability were observed: electrolytic, 52 %; ferrous fumarate, 30-35 %; Sun Active, 78 %; Ferrochel, 125 %; Na(2)FeEDTA, 291 %. Recent human studies have shown similar data with regard to Ferrochel, FeSO4 and Na(2)FeEDTA, with the latter being more bioavailable. Our phase-2 studies indicated that the addition of milk to FeSO(4)-fortified cereal increased Fe availability, but this availability was markedly decreased by the addition of coffee to the digest. Conversely, a loss in availability from Na(2)FeEDTA was observed with the addition of milk; however, the addition of coffee did not markedly affect Fe availability from this form. In phase-3 studies we observed increased Fe availability upon the addition of milk to cereals containing Ferrochel, FeSO(4), Sun Active, a mixture of reduced Fe and Na(2)FeEDTA or reduced Fe. For these forms we did not assess the behaviour after the addition of coffee. In conclusion, when considering possible fortificants for optimizing Fe bioavailability within a foodstuff, it is of paramount importance to consider the interaction between the fortified foodstuffs and other components of the meal (such as milk and coffee with a breakfast).     

Effect of EDTA on the bioavailability to rats of fortification iron used in Egyptian balady bread

The effectiveness of EDTA compounds on iron fortificants for potential use in Egyptian balady bread was tested in sixty Sprague-Dawley weanling male rats by the haemoglobin regeneration efficiency (HRE) method. To confirm HRE-derived findings, eight groups of ten animals were repleted with a modified American Institute of Nutrition (1977; AIN) 76A diet, fortified with ferric phosphate, electrolytic Fe, carbonyl Fe or ferrous sulphate, with and without ascorbic acid. Results without ascorbic acid were comparable to findings of a human study by Forbes et al. (1989). Bioavailability of EDTA-enhanced fortificants, FeSO4 + Na2EDTA and NaFe(III)EDTA, was compared with that of FeSO4 in six groups of ten animals repleted with a ground Egyptian bread meal or a casein-based AIN diet fortified with one of the three compounds. Addition of either EDTA compound significantly increased bioavailability of Fe in Egyptian balady bread. When present in the less inhibitory casein meal, however, FeSO4 + Na2EDTA fortification was significantly less effective than NaFe(III)EDTA or the reference FeSO4. Results indicate that NaFe(III)EDTA may be the fortificant of choice in a mixed diet. Further study of EDTA-enhanced Fe fortificants is needed.     

Particle size reduction and encapsulation affect the bioavailability of ferric pyrophosphate in rats

Particle size is an important determinant of Fe absorption from poorly soluble Fe compounds in foods. Decreasing the particle size of elemental iron powders increases their absorption. The effect of a reduction in particle size on the bioavailability of ferric pyrophosphate (FePP) is unclear. Encapsulation of iron compounds for food fortification may protect against adverse sensory changes, but at the same time may reduce bioavailability. The hemoglobin (Hb) repletion method in weanling Sprague-Dawley rats (n = 100) was used to compare the relative bioavailability (RBV) of 4 forms of FePP: 1) regular FePP [mean particle size (MPS) approximately 21 microm]; 2) MPS approximately 2.5 microm; 3) MPS approximately 2.5 microm encapsulated in hydrogenated palm oil; and 4) MPS approximately 0.5 microm with emulsifiers. The RBV compared with ferrous sulfate was calculated by the slope-ratio technique. The RBV was 43% for encapsulated MPS approximately 2.5 microm, significantly lower than the other FePP compounds (P < 0.05), 59% for the regular FePP, and 69% for MPS approximately 2.5 microm, not different from each other but significantly lower than ferrous sulfate (P < 0.05), and 95% for emulsified MPS approximately 0.5 microm, comparable to ferrous sulfate. Encapsulation of FePP with hydrogenated palm oil at a capsule:substrate ratio of 60:40 decreased RBV. Particle size reduction increases the RBV of FePP and may make this compound more useful for food fortification.     

Low bioavailability of carbonyl iron in man: studies on iron fortification of wheat flour

The bioavailability in man of commercially available elemental iron powders is unknown despite their extensive use for fortification of flour. Carbonyl iron, which is widely used in Europe, is considered as one of the best reduced iron powders based on studies both in vitro and in animals. In this study, a 55Fe labeled carbonyl iron was prepared by neutron irradiation and used to fortify wheat flour. The native iron of the wheat was extrinsically labeled by 59FeCl3. Doubly labeled wheat rolls were served with different meals. The ratio of absorbed 55Fe/59Fe is a direct measure of the fraction of carbonyl iron that joins the nonheme iron pool and is made potentially available for absorption. This relative bioavailability of carbonyl iron was unexpectedly low and varied from 20 to 5% when the iron fortified wheat rolls were served with different meals. The baking process did not change the relative bioavailability nor the addition of ascorbic acid. The low and variable bioavailability of carbonyl iron in man, makes it necessary to reconsider the rationale of using elemental iron powders for the fortification of foods for human consumption.     

Iron status and food matrix strongly affect the relative bioavailability of ferric pyrophosphate in humans

BACKGROUND: Although ferric pyrophosphate is a promising compound for iron fortification of foods, few data are available on the effect of food matrices, processing, and ascorbic acid on its bioavailability. OBJECTIVE: We compared the relative bioavailability (RBV) of ferrous sulfate in an experimental form of micronized dispersible ferric pyrophosphate (MDFP) in a wheat-milk infant cereal given with and without ascorbic acid with the RBV of MDFP from a processed and unprocessed rice meal. DESIGN: A crossover design was used to measure iron absorption in young women (n = 26) from test meals fortified with isotopically labeled [57Fe]-MDFP and [58Fe]-ferrous sulfate, based on erythrocyte incorporation of stable isotope labels 14 d later. RESULTS: Geometric mean iron absorption from the wheat-based meal fortified with MDFP was 2.0% and that from the meal fortified with ferrous sulfate was 3.2% (RBV = 62). The addition of ascorbic acid at a molar ratio of 4:1 to iron increased iron absorption from MDFP to 5.8% and that from ferrous sulfate to 14.8% (RBV = 39). In the rice meals, mean iron absorption from MDFP added to the rice at the time of feeding was 1.7%, and that from ferrous sulfate was 11.6% (RBV = 15). The mean iron absorption from MDFP extruded into artificial rice grains was 3.0% and that from ferrous sulfate in unprocessed rice was 12.6% (RBV = 24). Sixteen of 26 subjects were iron deficient. Iron status was a highly significant predictor of the RBV of MDFP (P < 0.001). CONCLUSION: RBV of the experimental MDFP varied markedly with food matrix and iron status. Assigning a single RBV value to poorly soluble compounds may be of limited value in evaluating their suitability for food fortification.     

Effects of ascorbic acid, phytic acid and tannic acid on iron bioavailability from reconstituted ferritin measured by an in vitro digestion-Caco-2 cell model

The effects of ascorbic acid (AA), phytate and tannic acid (TA) on Fe bioavailability from Fe supplied as reconstituted ferritin were compared with FeSO4 using an in vitro digestion-Caco-2 cell model. Horse spleen apoferritin was chemically reconstituted into an animal-type ferritin (HSF) and a plant-type ferritin (P-HSF) according to the typical ratios of Fe:P found in these molecules. In the presence of AA (Fe:AA molar ratio of 1:20), significantly more Fe was absorbed from FeSO4 (about 303 %), HSF (about 454 %) and P-HSF (about 371 %) when compared with ferrous sulfate or ferritin without AA. Phytic acid (PA; Fe:PA molar ratio of 1:20) significantly reduced Fe bioavailability from FeSO4 (about 86 %), HSF (about 82 %) and P-HSF (about 93 %) relative to FeSO4 and the ferritin controls. Treatment with TA (Fe:TA molar ratio of 1:1) significantly decreased Fe bioavailability (about 97 %) from both FeSO4 and the ferritin samples. AA was able to partially reverse the negative effect of PA (Fe:PA:AA molar ratio of 1:20:20) on Fe bioavailability but did not reverse the inhibiting effect of TA (Fe:TA:AA molar ratio of 1:1:20) on Fe bioavailability from ferritin and FeSO4. Overall, there were no significant differences in bioavailable Fe between P-HSF, HSF or FeSO4. Furthermore, the addition of AA (a known promoter) or the inhibitors, PA and TA, or both, did not result in significant differences in bioavailable Fe from ferritin relative to FeSO4. The results suggest that Fe in the reconstituted ferritin molecule is easily released during in vitro digestion and interacts with known promoters and inhibitors.     

The enhancement of nonheme iron bioavailability by beef protein in the rat

Beef protein was found to enhance the bioavailability of nonheme iron in the rat. Anemic rats were fed diets containing soy protein concentrate or rice bran as the source of nonheme iron with either lactalbumin or distilled water-washed beef, which was heme free. The criteria used to determine the relative biological value (RBV) of iron was the difference between the products of final hemoglobin x final weight and initial hemoglobin x initial weight during the repletion period. Animals fed diets with only lactalbumin as a source of dietary protein and graded levels of FeSO4 (RBV of FeSO4 = 100%) served as controls. The RBV of the endogenous iron in soy protein and rice bran was found to be 91 and 46%, respectively. Substituting washed beef for lactalbumin increased the RBV of soy protein iron to 96% (results not statistically significant) and of rice bran iron to 75% (results significant, P less than or equal to 0.05). These findings demonstrate the "meat factor" effect in the rat for the first time. Two days after completion of the 11-d hemoglobin regeneration period, the apparent absorption of iron was measured during a 60-h balance period. The apparent absorption of iron by rats fed diets containing beef tended to be higher, compared to animals fed diets containing lactalbumin.     

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.     

An irradiated electrolytic iron fortificant is poorly absorbed by humans and is less responsive than FeSO4 to the enhancing effect of ascorbic acid

Despite extensive use, information on the bioavailability of elemental iron powders to humans, as influenced by dose and other dietary constituents, is limited. Three experiments were conducted to assess the absorption of electrolytic iron powder relative to FeSO4, as affected by iron dose and by ascorbic or phytic acid. Iron absorption by 56 volunteers was measured from a farina cereal breakfast radiolabeled with 59FeSO4 or an electrolytic 55Fe powder irradiated by neutron activation. Absorption was determined from whole-body counting (59Fe) and blood isotope incorporation 2 wk later. Absorption of iron from the irradiated electrolytic powder was 5-15% that of FeSO4. Ascorbic acid (approximately 160 mg) enhanced iron absorption from FeSO4 by almost 4-fold but only doubled absorption from electrolytic iron (P for interaction < 0.01). Phytic acid from wheat bran inhibited iron absorption from FeSO4 and electrolytic iron by 73 and 50%, respectively (P for interaction, NS). Compared with 3 mg, a 20-mg dose reduced fractional absorption from FeSO4, but not electrolytic iron (P for interaction < 0.0001). Despite a much higher bioavailability (50% relative to FeSO4) of this same electrolytic iron when tested previously in a pig model, the bioavailability of the irradiated electrolytic iron was poor in humans. The diminished influence of ascorbic acid on the absorption of less soluble iron sources such as elemental iron powders may be an important consideration when choosing iron fortificants.     

New insights about iron bioavailability inhibition by zinc

OBJECTIVE: We measured the effects of lower and higher doses of zinc (Zn) given as an aqueous solution on the bioavailability of iron (Fe). METHODS: Fourteen healthy subjects received a solution with 0.5 mg of elemental Fe as ferrous sulfate given alone or with 0.59 mg of Zn as zinc sulfate (molar ratio Zn:Fe 1:1). Fourteen days after they received a second solution with 10 mg of Fe given alone or with 11.71 mg of Zn (molar ratio Zn:Fe 1:1). Iron bioavailability was assessed by erythrocyte incorporation of iron radioisotopes (55)Fe and (59)Fe. RESULTS: No significant effect of Zn on Fe bioavailability was observed at lower doses; however, at higher doses Fe bioavailability was inhibited by 56% (P < 0.001, repeated measures analysis of variance). CONCLUSION: The inhibitory effect of Zn on Fe bioavailability depends on the total amount of both minerals present in the intestinal lumen. This fact should be considered when designing a supplementation program if Fe and Zn are to be provided together.     

Serum iron curves can be used to estimate dietary iron bioavailability in humans

Erythrocyte incorporation of isotopic iron (Fe) is the standard method for assessing iron bioavailability, but the process is expensive, technically difficult, and gives no information on the kinetics of absorption. The main objective of this study was to validate serum Fe curves as measures of dietary iron absorption because previous work demonstrated that serum iron curves can be generated with iron doses as low as 5-20 mg and that up to 20 mg iron can be added to meals without affecting relative absorption. In 3 studies, groups (n = 10, 10, 21) of Fe-deficient, mildly anemic women consumed meals of varying calculated Fe bioavailability, with and without added ferric chloride (10 mg Fe). Blood samples were collected at baseline and every 30 min for 4 h after the meal. Serum Fe concentrations were measured. Areas under the serum Fe curves and peak concentrations were used in different models to estimate Fe absorption and uptake. In 21 subjects, (58)Fe-enriched ferric chloride was added to the meals, and blood was taken 2 wk later to calculate red cell isotope incorporation. The addition of 10 mg Fe to test meals produced measurable serum iron curves even when the meal Fe bioavailability was low. Serum Fe curves were highly reproducible and were affected as expected by food composition. Even the single measurement at the estimated time of peak iron concentration was correlated significantly with erythrocyte incorporation of (58)Fe (r = 0.72, P < 0.0001). Hence the extent and rate of absorption of nonheme iron from meals, rather than in individuals, can be investigated with such subjects without the need for isotopes.     

Iron Bioavailability from Ferrous Ammonium Phosphate,Ferrous Sulfate,and Ferric Pyrophosphate in an Instant Milk Drink—A Stable Isotope Study in Children

Ferrous ammonium phosphate (FAP) is an iron salt that has been developed for the fortification of food matrices sensitive to color and flavor changes. The objective of the study was to measure iron absorption from FAP in young children and compare it to a previous evaluation of FAP in young women. A double-blind randomized crossover study with two parallel arms was used to evaluate the iron absorption from FAP added to reconstituted milk powder in comparison to that from ferrous sulfate (FeSO₄) and ferric pyrophosphate (FePP). Iron absorption was measured in 39 children aged 3- to 6-years-old using erythrocyte incorporation of stable Fe isotopes (⁵⁷Fe, ⁵⁸Fe). The geometric mean iron absorption in iron replete children from FAP, FeSO₄ and FePP from milk was 8.3%, 7.6% and 2.1%, respectively. Iron absorption from FAP and FeSO₄ fortified milk was not significantly different (p = 0.199); however, it was significantly higher than from FePP fortified milk (p < 0.001). Iron bioavailability from FAP and FePP relative to FeSO₄ (relative bioavailability (RBV)) was 110% and 33%, respectively. The RBV of FAP (110%) in iron replete children was higher than previously reported RBV (71%) in mainly iron deficient women. The difference in iron status between the children and women in the respective studies may explain the different RBV values and is discussed.