Iron absorption from infant foods

Effect of using commercial pre-packaged baby foods on the Fe intake of 7-8 months old infants

OBJECTIVES

To examine the potential effect on Fe intake of 7-8 months old infants if pre-packaged baby foods (PBF) were used as the sole source of complementary foods.

DESIGN

Based on the 7-d recommended feeding plan for 7-8 months old infants in Hong Kong (moderate Fe-fortified rice cereal with home-cooked meals), twenty-four modelling scenarios were created which comprised of two milk use modes (breastmilk v. infant formula), three modes of rice cereal use (no-rice cereal; non-Fe-fortified rice cereal and Fe-fortified rice cereal) and four baby foods usage modes (home-cooked meals; low-Fe PBF only; high-Fe PBF only and mixed PBF). The PBF were randomly selected in each of the models and substituted the original meals/snacks. The average daily Fe intakes of the modelled meal plans were compared with the Chinese estimated average requirement (EAR) and recommended nutrient intake (RNI) for Fe.

SETTING

Modelling study.

PARTICIPANTS

Not applicable.

RESULTS

In general, the infant-formula-based complementary feeding pattern (CFP) had higher average daily Fe intake when compared with breastmilk-based CFP. The Fe intakes of all scenarios under the breastmilk-based CFP were below the RNI and EAR, except for the fortified rice cereal meal plans with high-Fe or mixed PBF. For infant-formula-based CFP, the Fe intakes were close to or above the RNI regardless of types of PBF or rice cereal used.

CONCLUSIONS

The inclusion of fortified rice cereal was important in maintaining adequate Fe intake for infants, especially for breast-fed infants. The replacement of home-cooked meals by low-Fe PBF could potentially put infants at risk of Fe deficiency.

Umbilical Cord Erythroferrone Is Inversely Associated with Hepcidin, but Does Not Capture the Most Variability in Iron Status of Neonates Born to Teens Carrying Singletons and Women Carrying Multiples

BACKGROUND

The developing fetus requires adequate iron and produces its own hormones to regulate this process. Erythroferrone (ERFE) is a recently identified iron regulatory hormone, and normative data on ERFE concentrations and relations between iron status and other iron regulatory hormones at birth are needed.

OBJECTIVES

The objective of this study was to characterize cord ERFE concentrations at birth and assess interrelations between ERFE, iron regulatory hormones, and iron status biomarkers in 2 cohorts of newborns at higher risk of neonatal anemia.

METHODS

Umbilical cord ERFE concentrations were measured in extant serum samples collected from neonates born to women carrying multiples (age: 21-43 y; n = 127) or teens (age: 14-19 y; n = 164). Relations between cord blood ERFE and other markers of iron status or erythropoiesis in cord blood were assessed by linear regression and mediation analysis.

RESULTS

Cord ERFE was detectable in all newborns delivered between 30 and 42 weeks of gestation, and mean concentration at birth was 0.73 ng/mL (95% CI: 0.63, 0.85 ng/mL). Cord ERFE was on average 0.25 ng/mL lower in newborns of black as opposed to white ancestry (P = 0.04). Cord ERFE was significantly associated with transferrin receptor (β: 1.17, P < 0.001), ferritin (β: -0.27, P < 0.01), and hemoglobin (Hb) (β: 0.04, P < 0.05). However, cord hepcidin and the hepcidin:erythropoietin (EPO) ratio captured the most variance in newborn iron and hematologic status (>25% of variance explained).

CONCLUSIONS

Neonates born to teens and women carrying multiples were able to produce ERFE in response to neonatal cord iron status and erythropoietic demand. ERFE, however, did not capture significant variance in newborn iron or Hb concentrations. In these newborns, cord hepcidin and the hepcidin:EPO ratio explained the most variance in iron status indicators at birth.

Iron absorption during pregnancy is underestimated when iron utilization by the placenta and fetus is ignored

BACKGROUND

Maternal iron absorption during pregnancy can be evaluated using RBC incorporation of orally administered stable iron isotope. This approach underestimates true maternal absorption of iron as it does not account for absorbed iron that is transferred to the fetus or retained within the placenta.

OBJECTIVE

Our objective was to re-evaluate maternal iron absorption after factoring in these losses and identify factors associated with iron partitioning between the maternal, neonatal, and placental compartments.

METHODS

This study utilized data from stable iron isotope studies carried out in 68 women during the third trimester of pregnancy. Iron status indicators and stable iron isotopic enrichment were measured in maternal blood, umbilical cord blood, and placental tissue when available. Factors associated with iron isotope partitioning between the maternal, neonatal, and placental compartments were identified.

RESULTS

On average, true maternal absorption of iron increased by 10% (from 19% to 21%) after accounting for absorbed iron present in the newborn (P < 0.001), and further increased by 7%, (from 39% to 42%, P < 0.001) after accounting for iron retained within the placenta. On average, 2% of recovered tracer was present in the placenta and 6% was found in the newborn. Net transfer of iron to the neonate was higher in women with lower total body iron (standardized β = -0.48, P < 0.01) and lower maternal hepcidin (standardized β = -0.66, P < 0.01). In women carrying multiple fetuses, neonatal hepcidin explained a significant amount of observed variance in net placental transfer of absorbed iron (R = 0.95, P = 0.03).

CONCLUSIONS

Maternal RBC iron incorporation of an orally ingested tracer underestimated true maternal iron absorption. The degree of underestimation was greatest in women with low body iron. Maternal hepcidin was inversely associated with maternal RBC iron utilization, whereas neonatal hepcidin explained variance in net transfer of iron to the neonatal compartment.These trials were registered at clinicaltrials.gov as NCT01019096 and NCT01582802.

Prepregnancy Obesity Is Not Associated with Iron Utilization during the Third Trimester

BACKGROUND

An adequate maternal iron supply is crucial for maternal red blood cell (RBC) expansion, placental and fetal growth, and fetal brain development. Obese women may be at risk for poor iron status in pregnancy due to proinflammatory-driven overexpression of hepcidin leading to decreased iron bioavailability.

OBJECTIVE

The objective of this study was to determine the impact of prepregnancy (PP) obesity on third-trimester maternal iron utilization.

DESIGN

Using the stable isotope 57Fe, we measured iron utilization in the third trimester in PP obese [BMI (in kg/m2): ≥30] and nonobese (BMI: 18.5-29.9) women. We also assessed iron status, hepcidin, inflammation, erythropoietin, dietary iron intake, and gestational weight gain. Descriptive and inferential statistical tests (e.g., Student t test, Pearson correlation) were used for data analysis.

RESULTS

Fifty pregnant women (21 PP obese, 29 PP nonobese) were included. Mean age was 27.6 ± 6.8 y and mean gestational age at time of 57Fe administration was 32.7 ± 0.7 wk. Anemia (hemoglobin <11 g/dL for non-black and <10.2 g/dL for black women) affected 38% of women (43% PP obese compared with 35% PP nonobese; P = 0.55). Women with PP obesity had significantly higher C-reactive protein (8.5 compared with 3.4 mg/L, P = 0.0007) and total body iron corrected for inflammation (6.0 compared with 4.3 mg/kg, P = 0.04) compared with the nonobese women. There was no difference in serum hepcidin or iron utilization between the PP BMI groups.

CONCLUSION

This is the first study to assess the impact of PP obesity on maternal iron utilization. We found no difference in iron utilization in the third trimester of pregnancy in women with and without PP obesity. Despite higher frequency of anemia, women with PP obesity had less depleted body iron stores, suggesting some degree of iron sequestration. This finding should be followed up and extended to understand effects on fetal iron bioavailability.

Iron uptake and ferrokinetics in healthy male subjects of an iron-based oral phosphate binder (SBR759) labeled with the stable isotope (58)Fe

SBR759 is a novel polynuclear iron(III) oxide-hydroxide starch·sucrose·carbonate complex being developed for oral use in chronic kidney disease (CKD) patients with hyperphosphatemia on hemodialysis. SBR759 binds inorganic phosphate released by food uptake and digestion in the gastro-intestinal tract increasing the fecal excretion of phosphate with concomitant reduction of serum phosphate concentrations. Considering the high content of ∼20% w/w covalently bound iron in SBR759 and expected chronic administration to patients, absorption of small amounts of iron released from the drug substance could result in potential iron overload and toxicity. In a mechanistic iron uptake study, 12 healthy male subjects (receiving comparable low phosphorus-containing meal typical for CKD patients: ≤1000 mg phosphate per day) were treated with 12 g (divided in 3 × 4 g) of stable (58)Fe isotope-labeled SBR759. The ferrokinetics of [(58)Fe]SBR759-related total iron was followed in blood (over 3 weeks) and in plasma (over 26 hours) by analyzing with high precision the isotope ratios of the natural iron isotopes (58)Fe, (57)Fe, (56)Fe and (54)Fe by multi-collector inductively coupled mass spectrometry (MC-ICP-MS). Three weeks following dosing, the subjects cumulatively absorbed on average 7.8 ± 3.2 mg (3.8-13.9 mg) iron corresponding to 0.30 ± 0.12% (0.15-0.54%) SBR759-related iron which amounts to approx. 5-fold the basal daily iron absorption of 1-2 mg in humans. SBR759 was well-tolerated and there was no serious adverse event and no clinically significant changes in the iron indices hemoglobin, hematocrit, ferritin concentration and transferrin saturation.

Maternal hepcidin is associated with placental transfer of iron derived from dietary heme and nonheme sources

The determinants of placental transport of dietary iron remain largely uncharacterized. The objective of this research was to elucidate determinants of fetal Fe transfer from maternally ingested dietary heme and non-heme Fe. The study was undertaken in 19 pregnant females (16-32 y) who ingested intrinsically labeled (58)Fe-heme and a nonheme Fe source ((57)FeSO(4)) during the third trimester of pregnancy. At delivery, maternal and cord blood was obtained to assess neonatal (57)Fe and (58)Fe enrichment as a function of maternal/neonatal Fe status [serum ferritin (SF), transferrin receptor, hemoglobin (Hb), total body Fe, and hepcidin]. There was a greater percentage of maternally absorbed (58)Fe tracer present in the neonates compared to the (57)Fe tracer (5.4 ± 2.4 vs. 4.0 ± 1.6; P < 0.0001). Net dietary nonheme Fe (mg) and heme Fe (mg) transferred to the fetus were both inversely correlated with measures of maternal serum hepcidin (P = 0.002, r(2) = 0.43; P = 0.004, r(2) = 0.39) and SF (P = 0.0008, r(2) = 0.49; P = 0.003, r(2) = 0.41) and directly associated with neonatal Hb (P = 0.004, r(2) = 0.39; P = 0.008, r(2) = 0.35). The results of this study suggest that during pregnancy there appears to be preferential fetal use of maternally ingested Fe derived from a dietary, animal-based heme source compared to Fe ingested as ferrous sulfate. Maternal serum hepcidin and maternal/neonatal Fe status may play a role in placental uptake of dietary heme and nonheme Fe.

Dry cereals fortified with electrolytic iron or ferrous fumarate are equally effective in breast-fed infants

Precooked, instant (dry) infant cereals in the US are fortified with electrolytic iron, a source of low reactivity and suspected low bioavailability. Iron from ferrous fumarate is presumed to be more available. In this study, we compared a dry infant rice cereal (Cereal L) fortified with electrolytic iron (54.5 mg iron/100 g cereal) to a similar cereal (Cereal M) fortified with ferrous fumarate (52.2 mg Fe/100 g) for efficacy in maintaining iron status and preventing iron deficiency (ID) in breast-fed infants. Ascorbic acid was included in both cereals. In this prospective, randomized double-blind trial, exclusively breast-fed infants were enrolled at 1 mo and iron status was determined periodically. At 4 mo, 3 infants had ID anemia and were excluded. Ninety-five infants were randomized at 4 mo, and 69 (36 Cereal L, 33 Cereal M) completed the intervention at 9 mo. From 4 to 9 mo, they consumed daily one of the study cereals. With each cereal, 2 infants had mild ID, a prevalence of 4.2%, but no infant developed ID anemia. There were no differences in iron status between study groups. Iron intake from the study cereals was (mean ± SD) 1.21 ± 0.31 mg⋅kg(-1)⋅d(-1) from Cereal L and 1.07 ± 0.40 mg⋅kg(-1)⋅d(-1) from Cereal M. Eleven infants had low birth iron endowment (plasma ferritin < 55 μg/L at 2 mo) and 54% of these infants had ID with or without anemia by 4 mo. We conclude that electrolytic iron and ferrous fumarate were equally efficacious as fortificants of this infant cereal.

Utilization of iron from an animal-based iron source is greater than that of ferrous sulfate in pregnant and nonpregnant women

Heme iron absorption during pregnancy and the role of hepcidin in regulating dietary heme iron absorption remains largely unexplored. The objective of this research was to examine relative differences in heme (animal based) and nonheme (ferrous sulfate) iron utilization. This study was undertaken in 18 pregnant (ages 16-32 y; wk 32-35 of gestation) and 11 nonpregnant women (ages 18-27 y). Women were randomly assigned to receive both an animal-based heme meal (intrinsically labeled (58)Fe pork) and labeled ferrous sulfate ((57)Fe) fed on alternate days. Blood samples obtained 2 wk postdosing were used to assess iron status indicators and serum hepcidin and iron utilization based on RBC incorporation of iron isotopes. Heme iron utilization was significantly greater than nonheme iron utilization in the pregnant (47.7 ± 14.4 vs. 40.4 ± 13.2%) and nonpregnant women (50.1 ± 14.8 vs. 15.3 ± 9.7%). Among pregnant women, utilization of nonheme iron was associated with iron status, as assessed by the serum transferrin receptor concentration (P = 0.003; r(2) = 0.43). In contrast, heme iron utilization was not influenced by maternal iron status. In the group as a whole, women with undetectable serum hepcidin had greater nonheme iron utilization compared with women with detectable serum hepcidin (P = 0.02; n = 29); however, there were no significant differences in heme iron utilization. Our study suggests that iron utilization from an animal-based food provides a highly bioavailable source of dietary iron for pregnant and nonpregnant women that is not as sensitive to hepcidin concentrations or iron stores compared with ferrous sulfate.

Iron fortification of infant formula

The purpose of this review is to examine the need for and appropriate level of Fe fortification of infant formula, and to assess any adverse effects of Fe fortification. The appropriate level of Fe fortification of infant formula has been established through studies of Fe absorption or erythrocyte incorporation of Fe, and through clinical trials of formulas with varying levels of Fe that were aimed at preventing the development of Fe deficiency in participating infants. In addition, the effects of varying levels of Fe fortification on the absorption of other minerals and trace elements, and on the incidence of infection and immune function have been studied, as has the effect of adding bovine lactoferrin to formula. Studies of Fe absorption have shown that increasing the level of Fe fortification in formula does not significantly increase the amount absorbed, and that the addition of bovine lactoferrin is unlikely to further increase absorption of Fe. Quite different recommendations for the level of Fe fortification of formula are made in the USA and in Europe. The higher level (12 mg/l) commonly used in the USA is not well supported by the evidence from clinical trials that suggest that lower levels (4 mg/l or less) may be adequate to prevent the development of Fe deficiency. Higher levels of Fe fortification may also interfere with the absorption of other minerals such as Cu and Se. Concerns about potential adverse effects of Fe fortification on immune function and susceptibility to infections have been disproved as have concerns about associated gastrointestinal symptomatology. There are no clearly demonstrated advantages in using ‘follow-on’ formula with high Fe content (up to 13 mg/l) instead of the standard UK formulas with Fe fortification in the range 4–7 mg/l after the age of 6 months, although they may provide an important ‘safety net’ for the prevention of Fe deficiency in communities with weaning diets low in Fe.

Absorption and loss of iron in toddlers are highly correlated

For estimating the requirements for dietary iron, it is important to know the amount of iron that is lost from the body. Inevitable losses of iron have been determined in adult humans but not in infants or children. We administered (58)Fe, the least abundant stable isotope of iron, to free-living infants at 168 d of age (5.6 mo) and followed them to age 26 mo. There was no dietary restriction after isotope administration. Blood was obtained at regular intervals for determination of isotopic enrichment and indices of iron status. We estimated the quantity of circulating iron, noncirculating active iron, and storage iron at each age. The administered isotope equilibrated with total body iron by 13 mo of age. From 13 to 26 mo of age, we estimated inevitable loss and absorption of iron from the change in tracer abundance in circulating iron. The rate of decrease of tracer abundance was proportional to addition of tracee, i.e., absorption of iron. Conversely, the rate of decrease in quantity of tracer was proportional to removal of tracee, i.e., loss of iron. From 13 to 26 mo of age, iron absorption was (mean +/- SD) 0.49 +/- 0.13 mg/d and inevitable iron loss was 0.25 +/- 0.12 mg/d. Intersubject variability of iron loss and iron absorption was high, and iron loss and absorption were highly correlated (r = 0.789, P < 0.001). Iron stores were low throughout the study and decreased significantly from 13 to 26 mo of age, suggesting that iron absorption from the diet was inadequate to maintain or increase iron nutritional status. The data suggest that, in this cohort, which may be representative, the intake of bioavailable iron from 13 to 26 mo of age was insufficient to maintain iron nutritional status.

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.

Iron absorption during recovery from malnutrition

OBJECTIVE

In infants and children recovering from severe malnutrition, iron deficiency is common, and the ability to absorb iron during such recovery is uncertain. The objective of this study was to determine iron absorption during recovery from malnutrition.

METHODS

During the later stages of recovery from malnutrition, erythrocyte incorporation of orally administered 58Fe was determined as a surrogate for iron absorption. Based on four indices, subjects were classified as iron-sufficient, iron-deficient or indeterminate.

RESULTS

Of the 25 subjects, 9 were classified as iron sufficient, 5 as indeterminate and 11 as iron deficient; all but 5 had evidence of inflammation or infection. Geometric mean erythrocyte incorporation of 58Fe was 32.0% of the dose in the iron-deficient subjects, which was not significantly different (p = 0.073) than the 13.1% in the iron-sufficient subjects. Incorporation of 58Fe by the iron-sufficient subjects did not differ significantly from that by normal subjects in the same age range. Surprisingly, we found no correlation of erythrocyte incorporation of 58Fe and reticulocyte count.

CONCLUSIONS

Even in the presence of infection or inflammation, iron absorption by children during a late stage of recovery from malnutrition is not impaired.

Retention of iron by infants

Throughout the world, the most common nutritional deficiency disorder of infants is iron deficiency. Developing effective strategies for preventing iron deficiency requires detailed knowledge of iron retention under ordinary living conditions. For the adult population, such knowledge is at an advanced stage, but relatively little is known about infants. Many reports of iron retention by infants have been based on the assumption that, as in normal and iron-deficient adults, 80%-100% of newly absorbed iron is promptly incorporated into circulating erythrocytes, but this assumption is not supported by available data. This communication presents a review of iron retention by term and preterm infants, as determined by metabolic balance studies or (59)Fe whole-body counting studies, and it explores the relationship between iron retention and postnatal age, iron nutritional status, iron intake (or dose), and type of feeding.

Time course of and effect of dietary iron level on iron incorporation into erythrocytes by infants

As a part of our effort to explore various aspects of ferrokinetics in infancy, the present study was designed to determine the timing of entry of an orally ingested iron isotope into circulating erythrocytes, and the effect of the level of dietary iron [0.3 mg/100 kcal (418.4 kJ) vs. 1.8 mg/100 kcal] after isotope administration on erythrocyte incorporation of the isotope. We administered the stable isotope, (58)Fe, orally to 56-d-old and 168-d-old infants. All infants were fed a low-iron formula (LF) before and until 5 h after isotope administration. Thereafter, half the infants were fed a formula high in iron (HF group) while the remaining infants continued to receive the LF (LF group) for an additional 28 d. The quantity of (58)Fe in circulating erythrocytes increased from 14 to 28 d after isotope administration was nearly constant from 28 through 84 d of age (plateau value) and decreased between 84 and 112 d. Erythrocyte incorporation of (58)Fe was greater by the 168-d-old infants than by the 56-d-old infants, presumably because of the lesser iron stores of the older infants. In the 56-d-old infants, erythrocyte incorporation of (58)Fe was greater by the LF than by the HF group, but this difference was not significant in the 168-d-old infants. Thus, at least in younger infants, the level of iron intake after administration of an iron isotope affects erythrocyte incorporation of the isotope. The fact that less isotope was present in erythrocytes 112 d than 84 d after administration indicates that the life span of erythrocytes of infants, even beyond the immediate newborn period, is less than the 120-d life span of erythrocytes in the adult.

Iron is well absorbed by healthy adults after ingestion of double-fortified (iron and dextran-coated iodine) table salt and urinary iodine excretion is unaffected

Severe deficiencies of iron (Fe) and iodine (I) affect more than one third of the world's population. A table salt, fortified with I and Fe, would be useful in areas in which anemia and goiter coexist. However, interactions between the two minerals have prevented their simultaneous use as fortificants. A method has been developed to coat I with dextran such that after spraying onto table salt, Fe and I do not interact. Our objective was to determine the absorption of Fe and the urinary excretion of I from table salt when provided in meals designed to significantly inhibit or enhance Fe absorption. Subjects (n = 16) ingested Fe-enhancing and Fe-inhibiting meals containing 5 g of table salt with 0.39 micromol dextran-coated I as potassium iodide and 1 mg of Fe (ferrous fumarate labeled with 59Fe) per gram of salt. Subjects also received a reference dose of 3 mg of ferrous fumarate labeled with 59Fe to "correct" for interindividual variation in iron absorption at a later date. Measured by whole-body counting, Fe-absorption from the Fe-enhancing meal (36.2 +/- 12.0%, corrected; 13.5 +/- 13.8% uncorrected) was significantly higher than that from the Fe-inhibiting meal (7.4 +/- 11.3%, corrected; 4.0 +/- 8.4%, uncorrected) (P < 0.0001). Urinary excretion of iodine at baseline and postingestion were not significantly different (0.89 +/- 0.5 vs. 1.06 +/- 0.39 micromol/L, P < 0.47) and were within the normal range. We conclude that Fe was well absorbed but influenced by the composition of the meal and that urinary excretion of iodine was maintained in the normal range with dextran-coated iodine.

The influence of meat on nonheme iron absorption in infants

During weaning the infant has a high iron requirement, and highly available dietary iron is needed to ensure optimal iron status. Muscle tissue has been identified as an enhancer of nonheme iron absorption in adults, although the influence of meat on nonheme iron absorption in infants has not been previously reported. The effect of the addition of 25 g of meat (lean beef) on nonheme iron absorption from a home-prepared vegetable purée meal (80 g of vegetables) was investigated in infants in the present study. The meals did not differ in their contents of other known enhancers or inhibitors of nonheme iron absorption. Incorporation of stable isotopes of iron (57Fe and 58Fe) into red blood cells 14 d after intake was used to measure iron absorption, using a cross-over design in eight healthy infants 43-49 wk of age. Nonheme iron absorption was significantly increased (p = 0.002) from the vegetable purée with added meat (geometric mean 15.0%) compared with the puréed vegetables (geometric mean 9.9%). These results thus suggest that meat is also an enhancer of nonheme iron absorption in infants and that nonheme iron absorption from weaning foods can be increased by the addition of meat.

Addition of rice cereal to formula does not impair mineral bioavailability

BACKGROUND

The effect of adding rice cereal to formula on calcium and iron bioavailability was studied.

METHODS

Fourteen healthy infants were studied at 2-week intervals to assess the absorption of calcium and iron from formula or formula mixed with rice cereal. Infants were randomly assigned to initiate the study either on a lactose-containing formula (F) or the same formula mixed with 6.5 g/dl of rice cereal (F + R). Calcium and iron absorption were determined using a multiple tracer approach in which calcium and iron isotopes were given orally mixed with either F or F + R and a different tracer of calcium given intravenously. Nine infants underwent calcium and iron studies and five underwent calcium studies only. A tracer amount of 46Ca was administered intravenously. Calcium absorption was determined as the ratio of the recovered oral versus intravenous tracer in the urine during the 24 hr after tracer administration. Iron incorporation into red blood cells (RBCs) was determined from the enrichment of the iron isotopes in the RBCs at 14 days after dosing.

RESULTS

Mean (+/- SD) percent absorption of calcium from F was 58% (+/- 13) and from F + R 57% (+/- 18). Absorption of iron from F was 5.8% (+/- 7) and from F + R 6.3% (+/- 4) (p = 0.06). Analyses of variance for repeated measures indicated no significant correlation between amount of calories, calcium, or iron ingested, and calcium or iron absorbed.

CONCLUSIONS

Adding rice cereal to formula does not impair bioavailability of calcium or iron from infant formulas. Because of the increased total calcium and iron in the mixture of formula and cereal, the overall amount of minerals absorbed from F + R may be greater than from formula alone.

Incidence of iron-deficiency anaemia and depleted iron stores among nine-month-old infants in Vancouver, Canada

The iron status and feeding practices of 434 infants in Vancouver were determined at 39 +/- 1 week of age. Iron-deficiency anaemia (haemoglobin < or = 101 g/L, or < or = 110 g/L with two or three abnormal results from tests of serum ferritin, zinc erythrocyte protoporphyrin and total iron binding capacity) occurred in 7% of infants. Low iron stores (serum ferritin < 10 micrograms/l) occurred in about 24% of infants. Iron-deficiency anaemia was significantly associated (p < 0.001) with duration of breastfeeding. The prevalence of iron-deficiency anaemia among infants breastfed for 8 months was 15%. At 39 weeks (9 months) of age, about 5% and 13% of the infants were bottle-fed with cows milk or low iron infant formula, respectively, and this was also significantly associated (p < 0.02) with low iron stores. Iron-fortified infant cereals had been introduced to 95% of the infants by six months of age. This study shows iron-deficiency anaemia is a problem among a significant number of nine-month-old infants in Canada, and is not explained by failure to introduce iron-fortified infant cereals.

Erythrocyte incorporation and absorption of 58Fe in premature infants treated with erythropoietin

We hypothesized that treatment of very low birth weight premature infants with r-HuEPO would increase erythrocyte incorporation and gastrointestinal absorption of iron. Infants with birth weights < or = 1.25 kg and gestational ages < 31 wk were randomized to receive 6 wk of 500 U of r-HuEPO/kg/wk (epo group, n = 7) or placebo (placebo group, n = 7). All infants received daily enteral supplementation with 6 mg of elemental iron per kg. An enteral test dose of a stable iron isotope, 58Fe, was administered after the 1st ("early dosing") and 4th ("late dosing") wk of treatment. Mean (+/-SD) erythrocyte incorporation of the dose of 58Fe administered determined 2 wk after early dosing was significantly greater in the epo group compared with the placebo group (4.4% +/- 1.6 versus 2.0 +/- 1.4%, p = 0.013). In contrast, after late 58Fe dosing, there was no difference between groups in incorporation (3.8 +/- 1.6% versus 5.5 +/- 2.7%). Within the epo group, percentage erythrocyte incorporation of 58Fe did not differ between early and late dosing, whereas in the placebo group it increased 3-fold (p < 0.01). Percentage absorption of 58Fe was not different between the epo and placebo groups after both early dosing (30 +/- 22% versus 34 +/- 8%) and late dosing (32 +/- 9% versus 31 +/- 6%). Absorption of nonlabeled elemental iron and 58Fe were significantly correlated with one another. The percentage of the absorbed 58Fe dose incorporated into Hb was not different between groups. We conclude that, although erythropoietin treatment stimulates erythrocyte iron incorporation in premature infants, it has no effect on iron absorption at the r-HuEPO dose studied.

Erythrocyte incorporation of iron is similar in infants fed formulas fortified with 12 mg/L or 8 mg/L of iron

Although feeding of formulas with iron concentration of 215 mumol/L (12 mg/L) is a reliable means of preventing iron deficiency, high intakes of iron may adversely affect absorption of copper and zinc. Because data are not available to establish whether fortification at a lower level would result in equivalent iron absorption, we tested the hypothesis that iron absorption is greater by infants fed formulas with an iron concentration of 215 mumol/L (12 mg/L) than by those fed formulas with an iron concentration of 143 mumol/L (8 mg/L). Fifty-two normal infants entered the study at 112 +/- 4 d of age, and 46 of these were successfully studied until 196 d of age. Using the stable isotope 58Fe, we determined erythrocyte incorporation of iron by infants fed Formula 8 [iron approximately 143 mumol/L (8 mg/L)] and by infants fed Similac with Iron [iron approximately 215 mumol/L (12 mg/L)]. On each of three test days beginning at 154 d of age, a major portion of the formula was labeled with 58Fe. Geometric mean erythrocyte incorporation of iron adjusted for plasma ferritin concentration at 168 d of age was 4.82 mumol/d (0.269 mg/d) by infants fed Formula 8 and 5.21 mumol/d (0.291 mg/d) by infants fed Similac with Iron. Corresponding values at 196 d of age were 5.12 and 5.41 mumol/d (0.286 and 0.302 mg/d). The differences in quantity of iron incorporated into erythrocytes by infants fed Formula 8 and Similac with Iron were not statistically significant (P = 0.66 at 168 d of age, P = 0.75 at 196 d of age) and were judged to be nutritionally trivial. Because we were unable to provide support for our hypothesis that iron absorption is greater by infants fed formulas providing 215 mumol (12 mg) of iron per liter than by those fed formulas providing 143 mumol (8 mg) of iron per liter, we conclude that, pending the results of further studies, It is reasonable to decrease the iron concentration of iron-fortified infant formulas.

Strategies for the prevention of iron deficiency: iron in infant formulas and baby foods

Iron deficiency is the most prevalent nutrition deficiency among infants and young children in industrialized as well as developing countries. It is a condition that is preventable through appropriate dietary measures. The infant born at term is endowed with a sizable amount of iron, which allows the infant to be fed a nearly iron-free diet (e.g., breast milk) for 4-6 months without becoming overtly iron deficient. This has led some to conclude that depletion of iron stores in healthy infants is a normal and, hence, innocuous process that usually gives way to gradual repletion of iron stores as dietary diversification leads to greater iron intakes. Preservation of maternal iron stores at the expense of infant iron stores may have offered survival advantages to the human species during evolution. But there is no evidence that depletion of iron stores can offer advantages to infants in industrialized or developing countries. On the contrary, there is ample documentation of shortterm as well as long-term adverse effects from iron deficiency. Prudence therefore dictates that a high priority be assigned to the prevention of iron depletion and deficiency among infants and young children worldwide.

Application of magnetic sector thermal ionization mass spectrometry to studies of erythrocyte iron incorporation in small children

The optimal evaluation of iron metabolism requires the administration of two isotopes of iron. However, high-precision measurement of isotopic ratios from blood samples obtained after administration of two stable isotopes of iron to human subjects has not previously been reported. Using a cation-exchange system to isolate iron from blood samples, we found that high-precision (< 0.2%) measurements of 58Fe/56Fe and 57Fe/56Fe could be performed using magnetic sector thermal ionization mass spectrometry. Clinical studies in four 1-year-old infants showed that this technique could be used to demonstrate a lower rate of iron absorption in small children given an iron supplement (57Fe) with milk compared to those given iron (58Fe and ferrous sulfate) with ascorbic acid. This technique will enable the evaluation of iron metabolism in populations in whom the use of radioactive iron tracers is not appropriate.

Minerals and trace elements in infant nutrition

Little information is available on absorption and metabolism of minerals and trace elements during infancy. The lack of data is related to the methodological problems involved in these studies. By using stable isotopes as labels, studies can be conducted in infants without introducing exposure to radiation, or any other risk, and studies on bioavailability of minerals and trace elements during early life can therefore be performed. This paper discusses results from studies of trace element/mineral absorption and metabolism in infants, based on stable isotope techniques.

A double stable isotope technique for measuring iron absorption in infants

A stable isotope technique has been developed which uses 57Fe and 58Fe as labels and which enables the simultaneous measurement of Fe absorption from two test meals in infants. The method was evaluated by measuring Fe absorption from a commercial whey-adjusted infant formula in nine healthy infants aged 13-25 weeks. Each infant was fed 210 ml formula, labelled with either 57Fe or 58Fe, on four consecutive mornings, in random order. The total Fe content in each feed was 2.5 mg Fe; either as 2.5 mg 57Fe, or 0.6 mg 58Fe plus 1.9 mg Fe with normal isotopic composition. Isotopic enrichment of Fe in erythrocytes was measured by thermal ionization mass spectrometry 14 d after the last administration, and Fe absorption was calculated based on isotope ratio shifts, total circulating Fe and intake of each isotope. Geometric mean absorption for the 57Fe and 58Fe labels was 6.72 and 6.58% respectively, and the absorption of the two isotopes was not significantly different (Student's paired t test). By this technique, paired comparisons of Fe absorption can be obtained and systematic studies of the influence of dietary factors on Fe absorption during infancy can be conducted.

Low iron stores in infants and children with treated phenylketonuria: a population at risk for iron-deficiency anaemia and associated cognitive deficits

A retrospective study of 53 patients with phenylketonuria (PKU), whose disease was managed with a low-phenylalanine diet, revealed a high incidence of iron depletion (as reflected by subnormal serum ferritin concentrations). Serum ferritin concentrations under 10 micrograms/l were found in one out of six infants aged 5-12 months. Concentrations under 16 micrograms/l were found in 16 of 22 children aged 1-3 years and in 11 of 25 children aged 4-12 years. Dietary iron, estimated from prescribed intakes of medical foods, exceeded the Canadian recommended nutrient intake, suggesting that low stores of iron may be secondary to reduced bioavailability and absorption of iron. These findings suggest that the current dietary management of PKU is associated with an increased risk for low iron stores. Investigators have reported an association in young children between iron-deficiency anaemia and both cognitive and motor disturbances. Children with PKU, already at risk of neurological damage because of phenylalanine neurotoxicity, may be at increased risk as a result of iron depletion. Serum ferritin as well as haemoglobin concentration should be monitored, along with plasma phenylalanine and tyrosine, to ensure optimum treatment of affected children.

Interactions between infections, malnutrition and iron nutritional status in Pakistani infants. A longitudinal study

The interactions between infections, malnutrition and poor iron nutritional status in infants at weaning ages are poorly defined. Therefore, four groups of infants from an area with a high incidence of malnutrition (Lahore, Pakistan) were enrolled in a prospective, randomized nutritional intervention study. Between 122 and 365 days of age, the infants from one community received either a milk cereal without iron fortification (n = 29), a milk cereal fortified with ferrous fumarate (7.5 mg/100 g; n = 30), or a milk cereal fortified with ferric-pyrophosphate (7.5 mg/100 g; n = 27). Forty-four infants from a neighbouring community did not receive a nutritional supplement and served as the control group. Calculated mean daily energy- and protein intake with the cereals was between 259-287 kcal, and 9.6-10.6 g at 12 months of age, respectively. Mean daily iron intake with the fortified cereals was between 4.1-5.1 mg at corresponding age. Nutritional supplementation resulted in significantly lower incidence of malnutrition and higher weight gain. Incidence of acute diarrhoea was significantly (p less than 0.05) lower in the supplemented groups. The infants fed the iron-fortified milk cereals had significantly higher hemoglobin (mean 10.4 vs. 9.8 g.dl-1) and serum ferritin (mean 13.3 vs. 8.5 ng.ml-1) values than the infants fed the non-fortified milk cereals. However, no differences in the incidence of infections were found between the supplemented groups. It is concluded that poor nutritional intake between 122 and 365 days of age substantially contributed to the high incidence of diarrhoea and malnutrition in Pakistani infants.

Nutritional anemias

Prevention of nutritional deficiencies should be attained by the consumption of a good diet. Unfortunately, in the case of iron, this is not always possible, and it is advantageous to fortify food with iron. Milk-based formulas and cereals are the most commonly used iron-fortified products in infancy and early childhood. Bioavailability of iron from cereals is low and more clinical studies on the field are necessary to demonstrate the effectiveness of iron-fortified cereals in infants and children of developing countries. Infections and excessive blood loss in infancy related to the use of fresh, pasteurized or powdered cow milk result in much of the anemia we currently see in industrialized countries. Vitamin A deficiency interacts with iron metabolism and recent intervention studies have shown that anemia in Vitamin A deficient children can be successfully treated with oral supplements.