Iron bioavailability in infants from an infant cereal fortified with ferric pyrophosphate or ferrous fumarate

BACKGROUND: Infant cereals are commonly fortified with insoluble iron compounds with low relative bioavailability, such as ferric pyrophosphate, because of organoleptic changes that occur after addition of water-soluble iron sources. OBJECTIVE: Our objective was to compare iron bioavailability from ferric pyrophosphate with an alternative iron source that is soluble in dilute acid, ferrous fumarate, and to evaluate the influence of ascorbic acid on iron bioavailability from ferrous fumarate in infants. DESIGN: Iron bioavailability was measured as the incorporation of stable iron isotopes into erythrocytes 14 d after administration of labeled test meals (25 g dry wheat and soy infant cereal, 100 g water, and 2.5 mg Fe as [57Fe]ferric pyrophosphate or [57Fe]ferrous fumarate). Ascorbic acid was added to all test meals (25 mg in study 1 or 25 or 50 mg in study 2). Infants were fed each test meal on 4 consecutive days under standardized conditions. The 2 different test meals within each study were administered 2 wk apart in a crossover design. RESULTS: Geometric mean iron bioavailability was significantly higher from [57Fe]ferrous fumarate than from [57Fe]ferric pyrophosphate [4.1% (range: 1.7-14.7%) compared with 1.3% (range: 0. 7-2.7%); n = 8, P = 0.008]. In this study, doubling the ascorbic acid content did not further enhance iron bioavailability; the geometric means (range) were 3.4% (1.9-6.6%) and 4.2% (1.2-18.7%) for the test meals with 25 and 50 mg ascorbic acid added, respectively (n = 9). CONCLUSION: Iron bioavailability from iron-fortified infant cereals can be improved by using an iron compound with high relative bioavailability and by ensuring adequate ascorbic acid content of the product.     

Erythorbic acid is a potent enhancer of nonheme-iron absorption

BACKGROUND: Erythorbic acid, a stereoisomer of ascorbic acid with similar physicochemical properties, is widely used as an antioxidant in processed foods. OBJECTIVES: The aims of the present study were to evaluate the effect of erythorbic acid on iron absorption from ferrous sulfate at molar ratios of 2:1 and 4:1 (relative to iron) and to compare the effect of erythorbic acid directly with that of ascorbic acid at a molar ratio of 4:1. DESIGN: Iron absorption from iron-fortified cereal was measured in 10 women on the basis of erythrocyte incorporation of stable iron isotopes ((57)Fe or (58)Fe) 14 d after administration. Each woman consumed 4 ferrous-sulfate-fortified test meals (containing 5 mg Fe/meal) with or without added erythorbic or ascorbic acid. The data were evaluated by use of paired t tests, and the results are presented as geometric means. RESULTS: Iron absorption from the test meal without any added enhancer was 4.1%. The addition of erythorbic acid (at molar ratios of 2:1 and 4:1 relative to iron) increased iron absorption 2.6-fold (10.8%; P < 0.0001) and 4.6-fold (18.8%; P < 0.0001), respectively. The addition of ascorbic acid (molar ratio of 4:1) increased iron absorption 2.9-fold (11.7%; P = 0.0004). At a molar ratio of 4:1, erythorbic acid was 1.6-fold (P = 0.0002) as potent an enhancer of iron absorption as was ascorbic acid. CONCLUSION: Although erythorbic acid is a potent enhancer of iron absorption, its lack of antiscorbutic activity limits its usefulness in iron-fortification programs. However, it may play a major role in enhancing iron bioavailability from mixed diets that include foods preserved with erythorbic acid.     

The efficacy of a local ascorbic acid-rich food in improving iron absorption from Mexican diets: a field study using stable isotopes

BACKGROUND: One potentially sustainable approach to improving iron status at the community level is to encourage the consumption of local ascorbic acid-rich foods, in conjunction with meals high in nonheme iron. OBJECTIVE: The study, conducted in rural Mexico, measured stable isotopes of iron to evaluate the effect on iron absorption of the addition of 25 mg ascorbic acid as agua de limón (limeade) to 2 typical meals per day for 2 wk. DESIGN: Fifteen nonpregnant, nonlactating, iron-deficient (ferritin < 12 microg/L) women (x +/- SD age: 28.3 +/- 7.7 y) fasted overnight and were brought to a community clinic. After an initial blood sample, subjects consumed 0.25 mg (57)Fe with both breakfast and lunch for 14 d. On day 29, another blood sample was taken, and a reference dose of 2.7 mg (58)Fe with 25 mg ascorbic acid was given. For the following 15 d, participants consumed 0.25 mg (57)Fe added to both breakfast and lunch with 25 mg ascorbic acid added to each meal as limeade. A final blood sample was taken on day 59. RESULTS: Iron absorption was calculated from recovery of isotopes in blood obtained 14 d after administration of each isotope. When 25 mg ascorbic acid as limeade was added to test meals twice a day for 2 wk, iron absorption increased significantly (P < 0.001) in every subject: the mean absorption rose from 6.6 +/- 3.0% to 22.9 +/- 12.6%. CONCLUSIONS: The consumption of 25 mg ascorbic acid as limeade twice daily with meals substantially improved iron absorption and may improve the iron status of nonpregnant, nonlactating, iron-deficient women.     

Iron absorption from a breakfast cereal: effects of EDTA compounds and ascorbic acid

Sodium iron ethylenediaminetetracetic acid (NaFeEDTA) has been recommended for food fortification programmes to improve iron status but its performance in commercial products has not been evaluated. The effect of EDTA on iron absorption from fortified cornflakes, given as part of a typical Western breakfast, was determined in a double-blind randomised study with 20 non-anaemic female volunteers, using experimentally prepared iron compounds, enriched with 58Fe, and faecal monitoring. Five meals were compared: hydrogen reduced iron, hydrogen reduced iron plus Na2EDTA (molar ratio EDTA:Fe 1:2), hydrogen reduced iron plus NaFe(III)EDTA at two different molar ratios (EDTA:total Fe 1:3 and 1:2), and hydrogen reduced iron plus 15 mg ascorbic acid (ascorbic acid:Fe 1.3:1). The iron and EDTA compounds were accurately weighed into gelatine capsules and taken with unfortified cornflakes, semi-skimmed milk and tea on two consecutive days; the iron dose per meal was 3.75 mg. Iron absorption from all five test meals was measured in each volunteer with a minimum wash-out period of 2 weeks between tests. Geometric mean iron absorption (%) from the 5 tests was 14.1, 17.6, 20.6, 24.4 and 17.5 respectively (equivalent to 0.5-0.9 mg absorbed iron). There was a significantly higher iron absorption from the mixture of reduced iron and NaFe(III)EDTA (EDTA:Fe 1:2) than from reduced iron alone (p = 0.014). It is not known whether the higher absorption was from reduced iron or NaFeEDTA or both. Absorption was not increased significantly with NaFe(III)EDTA (EDTA:Fe 1:3), Na2EDTA (EDTA:Fe 1:2) or ascorbic acid (15 mg).     

Iron and ascorbic Acid: proposed fortification levels and recommended iron compounds

An adequate supply of dietary iron during the 1st 24 mo of life is essential for preventing iron deficiency with its attendant negative effects on mental, motor and emotional development as well as later cognitive performance. Iron reserves and the small amount of highly bioavailable iron in human milk are adequate to satisfy the iron requirements of breast-fed infants of adequate birth weight for the 1st 6 mo of life. Thereafter, complementary foods, iron supplements or both are needed to meet this requirement. Complementary foods should not displace the consumption of human milk. The quantities eaten, particularly by younger infants, may therefore be quite small. As a consequence it is essential that the iron be supplied in a highly bioavailable form. This can be achieved by fortifying complementary foods with ferrous sulfate and ascorbic acid provided that the ascorbic acid is not lost during storage or meal preparation. Suggested fortification levels for ferrous sulfate and ascorbic acid for some types of complementary foods are given. The use of ferrous fumarate or an elemental iron powder instead of ferrous sulfate has not been evaluated adequately. There is a need to develop alternative strategies for improving iron bioavailability in complementary foods because it may not be possible to preserve ascorbic acid activity in many of them.     

Phytic acid degradation as a means of improving iron absorption

Phytic acid is a potent inhibitor of native and fortification iron absorption and low absorption of iron from cereal- and/or legume-based complementary foods is a major factor in the etiology of iron deficiency in infants. Dephytinization of complementary foods or soy-based infant formulas is technically possible but, as phytic acid is strongly inhibitory at low concentrations, complete enzymatic degradation is recommended. If this is not possible, the phytic acid to iron molar ratio should be decreased to below 1:1 and preferably below 0.4:1. Complete dephytinization of cereal- and legume-based complementary foods has been shown to increase the percentage of iron absorption by as much as 12-fold (0.99% to 11.54%) in a single-meal study when the foods were reconstituted with water. The addition of milk, however, inhibits iron absorption and overcomes the enhancing effect of phytic acid degradation. Dephytinization can therefore be strongly recommended only for cereal/legume mixtures reconstituted with water, especially low-cost complementary foods destined for infants in developing countries. In countries where infant cereals are consumed with milk, ascorbic acid addition can more easily be used to overcome the negative effect of phytic acid on iron absorption. Similarly with soy-based infant formulas, especially if manufactured from low-phytate isolates, ascorbic acid can be used to ensure adequate iron absorption.     

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.     

铁强化中国酱油的研究——Ⅱ、铁强化酱油的人体铁吸收试验

31名健康成年自愿者,男11名,年龄18—48岁,女20名,年龄34—52岁 (均系采取节育措施的育龄妇女),用同位素~(55)Fe和~(59)Fe外标食物,分两批作人体铁吸收试验。其结果为:上海生产出口的海鸥牌瓶装酱油,原有铁(15.8mg铁/100ml)的吸收率几何均数(下同)为6.95％,酱油强化铁量为121mg铁/100ml时的铁吸收率为4.36％,该种铁强化酱油再强化维生素C(按铁:维生素C=1:2克分子量)则铁的吸收率为8.25％,几乎增加一倍。以7.5ml(一餐用量)的铁强化酱油(75mg铁/100ml)含铁量为5.6mg进行烹调蔬菜,以大米为主食,该餐中总铁量为8.9mg,铁的吸收率为5.65％,铁的吸收量为0.5mg;该餐另加瘦猪肉100g,则铁的吸收率为9.69％,铁的吸收量为1.08mg,肉能促进铁吸收一倍;但在该蔬菜餐后饮用龙井绿茶150ml(1.5g干茶叶泡成)其铁的吸收率降至3.09％,铁的吸收量为0.27mg,降低近一半。因此,应用加铁量为75mg铁/100ml的铁强化酱油,如按每人每天平均酱油的消耗量为15—20ml铁吸收率为5.65％计算,则铁的吸收量为0.63—0.85mg,可以基本满足一般人群每天对铁的需要量要求。如该种铁强化酱油同时强化维生素C,以铁吸收率增加一倍计算,则可满足孕妇、乳母、月经过多妇女及正在生长发育的儿童青少年对铁的特殊需要。     

Improving iron absorption from a Peruvian school breakfast meal by adding ascorbic acid or Na2EDTA

BACKGROUND: Iron-fortified school breakfasts have been introduced in Peru to combat childhood iron deficiency. OBJECTIVE: We evaluated whether iron absorption from a school breakfast meal was improved by increasing the ascorbic acid content or by adding an alternative enhancer of iron absorption, Na2EDTA. DESIGN: In a crossover design, iron absorption from test meals was evaluated by erythrocyte incorporation of 58Fe and 57Fe. The test meals (wheat bread and a drink containing cereal, milk, and soy) contained 14 mg added Fe (as ferrous sulfate) including 2.0-2.6 mg 58Fe or 4.0-7.0 mg 57Fe. RESULTS: Geometric mean iron absorption increased significantly from 5.1% to 8.2% after the molar ratio of ascorbic acid to fortification iron was increased from 0.6:1 to 1.6:1 (P < 0.01; n = 9). Geometric mean iron absorption increased significantly from 2.9% to 3.8%, from 2.2% to 3.5%, and from 2.4% to 3.7% after addition of Na2EDTA at molar ratios relative to fortification iron of 0.3:1, 0.7:1, and 1:1, respectively, compared with test meals containing no added enhancers (P < 0.01; n = 10 for all). Iron absorption after addition of ascorbic acid (molar ratio 0.6:1) was not significantly different from that after addition of Na2EDTA (molar ratio 0.7:1). CONCLUSIONS: Ascorbic acid and Na2EDTA did not differ significantly in their enhancing effects on iron absorption at molar ratios of 0.6:1 to 0.7:1 relative to fortification iron. Additional ascorbic acid (molar ratio 1.6:1) increased iron absorption significantly. Increasing the molar ratio of Na2EDTA to fortification iron from 0.3:1 to 1:1 had no effect on iron absorption.     

Sodium iron EDTA [NaFe(III)EDTA] as a food fortificant: erythrocyte incorporation of iron and apparent absorption of zinc, copper, calcium, and magnesium from a complementary food based on wheat and soy in healthy infants

BACKGROUND: Phytic acid is a strong inhibitor of iron absorption from fortified foods. In adults, this inhibitory effect can be overcome by adding ascorbic acid with the iron fortificant or by using a "protected" iron compound such as NaFeEDTA. In addition, the use of NaFeEDTA as an iron fortificant has been reported to increase zinc absorption in adult women. No information is available on iron bioavailability from NaFeEDTA or the influence of NaFeEDTA on minerals and trace elements in infants. OBJECTIVE: We aimed to compare iron bioavailability from a complementary food based on wheat and soy fortified with either NaFeEDTA or ferrous sulfate plus ascorbic acid. The apparent absorption of zinc, copper, calcium, and magnesium was evaluated in parallel. DESIGN: Stable-isotope techniques were used in a crossover design to evaluate erythrocyte incorporation of iron 14 d after administration of labeled test meals and the apparent absorption of zinc, copper, calcium, and magnesium on the basis of fecal monitoring in 11 infants. RESULTS: Geometric mean erythrocyte incorporation of iron was 3.7% (NaFeEDTA) and 4.9% (ferrous sulfate plus ascorbic acid) (P = 0.08). No significant differences in the apparent absorption of zinc, copper, calcium, or magnesium were observed between test meals (n = 10). CONCLUSIONS: Iron bioavailability from a high-phytate, cereal-based complementary food fortified with either NaFeEDTA or ferrous sulfate plus ascorbic acid was not significantly different. NaFeEDTA did not influence the apparent absorption of zinc, copper, calcium, or magnesium. NaFeEDTA does not provide any nutritional benefit compared with the combination of a highly bioavailable iron compound and ascorbic acid.     

Enhancers of iron absorption: ascorbic acid and other organic acids

Ascorbic acid (AA), with its reducing and chelating properties, is the most efficient enhancer of non-heme iron absorption when its stability in the food vehicle is ensured. The number of studies investigating the effect of AA on ferrous sulfate absorption far outweighs that of other iron fortificants. The promotion of iron absorption in the presence of AA is more pronounced in meals containing inhibitors of iron absorption. Meals containing low to medium levels of inhibitors require the addition of AA at a molar ratio of 2:1 (e.g., 20 mg AA: 3 mg iron). To promote absorption in the presence of high levels of inhibitors, AA needs to be added at a molar ratio in excess of 4:1, which may be impractical. The effectiveness of AA in promoting absorption from less soluble compounds, such as ferrous fumarate and elemental iron, requires further investigation. The instability of AA during food processing, storage, and cooking, and the possibility of unwanted sensory changes limits the number of suitable food vehicles for AA, whether used as vitamin fortificant or as an iron enhancer. Suitable vehicles include dry-blended foods, such as complementary, precooked cereal-based infant foods, powdered milk, and other dry beverage products made for reconstitution that are packaged, stored, and prepared in a way that maximizes retention of this vitamin. The consumption of natural sources of Vitamin C (fruits and vegetables) with iron-fortified dry blended foods is also recommended. Encapsulation can mitigate some of the AA losses during processing and storage, but these interventions will also add cost. In addition, the bioavailability of encapsulated iron in the presence/absence of AA will need careful assessment in human clinical trials. The long-term effect of high AA intake on iron status may be less than predicted from single meal studies. The hypothesis that an overall increase of dietary AA intake, or fortification of some foods commonly consumed with the main meal with AA alone, may be as effective as the fortification of the same food vehicle with AA and iron, merits further investigation. This must involve the consideration of practicalities of implementation. To date, programs based on iron and AA fortification of infant formulas and cow's milk provide the strongest evidence for the efficacy of AA fortification. Present results suggest that the effect of organic acids, as measured by in vitro and in vivo methods, is dependent on the source of iron, the type and concentration of organic acid, pH, processing methods, and the food matrix. The iron absorption-enhancing effect of AA is more potent than that of other organic acids due to its ability to reduce ferric to ferrous iron. Based on the limited data available, other organic acids may only be effective at ratios of acid to iron in excess of 100 molar. This would translate into the minimum presence/addition of 1 g citric acid to a meal containing 3 mg iron. Further characterization of the effectiveness of various organic acids in promoting iron absorption is required, in particular with respect to the optimal molar ratio of organic acid to iron, and associated feasibility for food application purposes. The suggested amount of any organic acid required to produce a nutritional benefit will result in unwanted organoleptic changes in most foods, thus limiting its application to a small number of food vehicles (e.g., condiments, beverages). However, fermented foods that already contain high levels of organic acid may be suitable iron fortification vehicles.     

Erythrocyte incorporation of iron by infants: iron bioavailability from a low-iron infant formula and an evaluation of the usefulness of correcting erythrocyte incorporation values, using a reference dose or plasma ferritin concentrations

Bioavailability of iron (Fe) from a low-Fe infant formula was determined by erythrocyte incorporation of 58Fe 14 d after administration in ten healthy, non-Fe-deficient infants. Two feeding protocols were compared, with each infant acting as his/her own control. At 140 and 154 d of age, infants were fed 1000 g of 58Fe-labelled formula (1.44 mg total Fe/1000 g) as six feeds over 24 h (Protocol A) or as two feeds/day on three consecutive days (Protocol B). A water solution with 57Fe and ascorbic acid was given separately as a reference dose in both study protocols. Erythrocyte incorporation of 58Fe and 57Fe was determined by thermal ionisation mass spectrometry. Geometric mean 58Fe incorporation was 7.6% (range 3.3-13.5%) with Protocol A as compared to 10.6% (range 6.7-18.6%) with Protocol B (P = 0.05); paired t test. Inter-individual variability of 58Fe was not reduced by correcting for the incorporation of 57Fe from the reference dose, or by correcting for plasma ferritin concentration. Fractional erythrocyte incorporation of Fe from low-Fe infant formula was in the same range as our earlier published data on erythrocyte incorporation of Fe from human milk extrinsically labelled with 58Fe (Davidsson et al. 1994a). The methodological evaluations included in this study clearly indicate the importance of using standardised study protocols when evaluating Fe bioavailability in infants. Corrections of erythrocyte incorporation data based on plasma ferritin or erythrocyte incorporation of Fe from a reference dose were not found to be useful.     

Ascorbic acid: effect on ongoing iron absorption and status in iron-depleted young women

The effect of ascorbic acid on iron retention from a diet with predicted low iron bioavailability (containing minimal meat and ascorbic acid) was investigated in iron-depleted premenopausal women. Eleven women were depleted of storage iron (indicated by serum ferritin) through a combination of diet (5.0 mg Fe/2000 kcal for 67-88 d) and phlebotomy. They then consumed a diet containing 13.7 mg Fe/2000 kcal, supplemented with placebo or ascorbic acid three times daily (1500 mg total) with meals for 5.5 wk. Ascorbic acid improved apparent iron absorption (balance method) [38 +/- 2% (means +/- SEM) vs 27 +/- 2%]. Ascorbic acid also improved hemoglobin, erythrocyte protoporphyrins, and serum iron but not hematocrit, serum ferritin, iron-binding capacity, or transferrin saturation. In iron-depleted women consuming a diet with predicted poor iron availability, ascorbic acid supplementation enhanced body iron retention for 5.5 wk.     

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.     

Studies on the bioavailability of zinc in man. III. Effects of ascorbic acid on zinc absorption

As ascorbic acid is known to enhance the absorption of dietary iron and to inhibit the absorption of dietary copper, studies were undertaken to examine the effect of ascorbic acid on the bioavailability of zinc in human subjects. The index of absorption was the change in plasma zinc concentration after a 110-mg aqueous dose of ZnSO4.7H2O (containing 25 mg of elemental zinc). Doses of 0.5, 1.0, and 2.0 g of ascorbic acid, representing a spectrum of Zn:ascorbic acid molar ratios from the dietary to the pharmacological range, failed to produce any significant change in the pattern of zinc absorption. Moreover, 2.0 g of ascorbic acid, equivalent to a Zn:ascorbic acid ratio of 0.145 failed to improve the absorption of 108 mg of elemental zinc incorporated into 120 g of black bean gruel. Ascorbic acid over a range of dosages commonly consumed by man had no demonstrable effect on the absorption of inorganic zinc.     

Caco-2 cells can be used to assess human iron bioavailability from a semipurified meal

A Caco-2 cell model with extrinsic radioiron was used to evaluate the effect of dietary factors on nonheme iron bioavailability from a semipurified meal. Study 1 was conducted to evaluate the effect of enhancers (ascorbic acid) and inhibitors (bran, phytate and tea) on iron bioavailability when added to semipurified meal containing egg albumen as a protein source. The effect of various proteins [bovine serum albumin (BSA), casein, beef and soy] on iron bioavailability was evaluated in Study 2 by substituting the above protein sources for egg albumen. Protein solubilization following in vitro digestion for individual test meals was not significantly different from the control. On the other hand, nonheme iron solubilization (0.8+/-0.0 to 5.9+/-0.3 vs. 4.9+/-0.8 mg/L) varied significantly. The total iron uptake for each meal was calculated based on the percentage of radioiron taken up and transported by Caco-2 cells and the amount of nonheme iron present in uptake solutions. Iron uptake ratios represent test/control values. With the exception of BSA and ascorbic acid, the effect of dietary factors was similar to that found in humans reported in the literature. A significant correlation (r = 0.97; P<0.0001) was found between the published human absorption data and the iron uptake by the Caco-2 cells. The results of our study indicate the usefulness of Caco-2 cells in assessing human iron absorption and the feasibility of this cell model in studying iron bioavailability from various food combinations, otherwise not easily performed in humans.     

Estimation of iron bioavailability in adolescents' meals and snacks

Dietary iron bioavailability was calculated from 24-hour food records of 224 adolescents. Eating patterns related to high iron bioavailability were identified. Indicators of dietary iron adequacy calculated in this study were the amount of total iron, the amount of available iron, and the percent bioavailability. Mean daily iron intakes were 16.1 mg for boys and 11.1 mg for girls. Estimation of daily iron bioavailability showed that mean available iron from boys' diets, 1.38 mg, and from girls' diets, 0.91 mg, was not only below recommended levels but also below 10% bioavailability, the basis of the RDA for iron. Diets that met recommended levels of available iron had unusually high amounts of energy, ascorbic acid, and animal tissue foods. Patterns of iron bioavailability differed among eating occasions but were similar for boys and girls. The breakfast meal was lowest in the three indicators of dietary iron adequacy; the evening meal was highest. Snacks contributed substantial amounts of food energy but little available iron to the adolescents' diets. If, at each eating occasion, adolescents include foods that enhance iron absorption and foods that are rich in iron, they will increase amounts of available iron in their diets.     

Iron bioavailability from iron-fortified Guatemalan meals based on corn tortillas and black bean paste

BACKGROUND: Corn masa flour is widely consumed in Central America and is therefore a potentially useful vehicle for iron fortification. OBJECTIVE: The goal was to evaluate the bioavailability of iron from meals based on corn tortillas and black bean paste that were fortified with ferrous fumarate, ferrous sulfate, or NaFeEDTA and to investigate the potential of Na(2)EDTA to increase the bioavailability of iron from ferrous fumarate. DESIGN: With use of a crossover study design, iron bioavailability was measured in Guatemalan girls aged 12-13 y by a stable-isotope technique based on erythrocyte incorporation 14 d after intake. RESULTS: Geometric mean iron bioavailability from test meals fortified with ferrous fumarate was 5.5-6.2% and was not improved significantly by the addition of Na(2)EDTA at molar ratios of 1:1 relative to fortification iron or to the total iron content of the fortified corn masa flour. Geometric mean iron bioavailability from test meals fortified with ferrous sulfate was 5.5% and was significantly higher in test meals fortified with NaFeEDTA (9.0%; P = 0.009, paired t test). CONCLUSIONS: The bioavailability of iron from ferrous fumarate was not improved by the addition of Na(2)EDTA, contrary to what was previously shown for ferrous sulfate in other cereal-based meals. However, the bioavailability of iron from the test meal was significantly enhanced when NaFeEDTA replaced ferrous sulfate. These results support the use of NaFeEDTA in the fortification of inhibitory staple foods such as corn masa flour.     

Green tea or rosemary extract added to foods reduces nonheme-iron absorption

BACKGROUND: Phenolic compounds act as food antioxidants. One of the postulated mechanisms of action is chelation of prooxidant metals, such as iron. Although the antioxidative effect is desirable, this mechanism may impair the utilization of dietary iron. OBJECTIVE: We sought to determine the effect of phenolic-rich extracts obtained from green tea or rosemary on nonheme-iron absorption. DESIGN: Young women aged 19-39 y consumed test meals on 4 separate occasions. The meals were identical except for the absence (meal A) or presence (meal B) of a phenolic-rich extract from green tea (study 1; n = 10) or rosemary (study 2; n = 14). The extracts (0.1 mmol) were added to the meat component of the test meals. The meals were extrinsically labeled with either 55Fe or 59Fe and were consumed on 4 consecutive days in the order ABBA or BAAB. Iron absorption was determined by measuring whole-body retention of 59Fe and the ratio of 55Fe to 59Fe activity in blood samples. RESULTS: The presence of the phenolic-rich extracts resulted in decreased nonheme-iron absorption. Mean (+/-SD) iron absorption decreased from 12.1 +/- 4.5% to 8.9 +/- 5.2% (P < 0.01) in the presence of green tea extract and from 7.5 +/- 4.0% to 6.4 +/- 4.7% (P < 0.05) in the presence of rosemary extract. CONCLUSION: Phenolic-rich extracts used as antioxidants in foods reduce the utilization of dietary iron.     

Effects of different calcium sources on iron absorption in postmenopausal women

We measured the effect of calcium from food and supplement sources on whole-body retention of 59Fe in 19 normal postmenopausal women. Each woman received a placebo and 500 mg calcium from a mixed calcium citrate-malate salt (CCM), from orange juice plus CCM, and from milk after a test breakfast meal to which 59Fe had been added. The test meal contained 238 mg calcium. Whole-body countings of 59Fe were performed before and 30 min and 2 wk after each test meal. Retention of 59Fe was 8.3 +/- 1.1% (means +/- SEM) with placebo, 3.4 +/- 0.78% with milk, 6.0 +/- 0.97% with CCM, and 7.4 +/- 1.7% with CCM plus orange juice. When compared with placebo, milk and CCM significantly lowered iron retention (p less than 0.05) whereas CCM plus orange juice did not. The reduction with milk was greater than that with CCM (p less than 0.05) or CCM plus orange juice (p less than 0.05). The differences in the effects of these calcium sources on 59Fe retention may result from their varied contents of citric and ascorbic acids, known enhancers of iron absorption.