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

Prevalence of anemia and deficiency of iron, folic acid, and zinc in children younger than 2 years of age who use the health services provided by the Mexican Social Security Institute

BACKGROUND

In Mexico, as in other developing countries, micronutrient deficiencies are common in infants between 6 and 24 months of age and are an important public health problem. The objective of this study was to determine the prevalence of anemia and of iron, folic acid, and zinc deficiencies in Mexican children under 2 years of age who use the health care services provided by the Mexican Institute for Social Security (IMSS).

METHODS

A nationwide survey was conducted with a representative sample of children younger than 2 years of age, beneficiaries, and users of health care services provided by IMSS through its regular regimen (located in urban populations) and its Oportunidades program (services offered in rural areas). A subsample of 4,955 clinically healthy children was studied to determine their micronutrient status. A venous blood sample was drawn to determine hemoglobin, serum ferritin, percent of transferrin saturation, zinc, and folic acid. Descriptive statistics include point estimates and 95% confidence intervals for the sample and projections for the larger population from which the sample was drawn.

RESULTS

Twenty percent of children younger than 2 years of age had anemia, and 27.8% (rural) to 32.6% (urban) had iron deficiency; more than 50% of anemia was not associated with low ferritin concentrations. Iron stores were more depleted as age increased. Low serum zinc and folic acid deficiencies were 28% and 10%, respectively, in the urban areas, and 13% and 8%, respectively, in rural areas. The prevalence of simultaneous iron and zinc deficiencies was 9.2% and 2.7% in urban and rural areas. Children with anemia have higher percentages of folic acid deficiency than children with normal iron status.

CONCLUSION

Iron and zinc deficiencies constitute the principal micronutrient deficiencies in Mexican children younger than 2 years old who use the health care services provided by IMSS. Anemia not associated with low ferritin values was more prevalent than iron-deficiency anemia. The presence of micronutrient deficiencies at this early age calls for effective preventive public nutrition programs to address them.

Predictors of serum ferritin and serum soluble transferrin receptor in newborns and their associations with iron status during the first 2 y of life

BACKGROUND

Adequate iron status at birth may prevent iron deficiency in early childhood.

OBJECTIVES

We aimed to identify predictors of serum ferritin (SF) and serum soluble transferrin receptor (sTfR) in healthy newborns and to relate these iron indexes to iron status in the first 2 y of life.

DESIGN

Using bivariate correlations and linear regression, we related various factors in pregnancy to SF (n=363) and sTfR (n=350) in healthy, term infants. Measurements of cord SF and sTfR were compared with those of SF and sTfR at 6, 12, and 24 mo. All 4 measurements were available for 191 and 169 infants for SF and sTfR, respectively.

RESULTS

Geometric mean (and 95% CI) cord SF and sTfR measurements were 159 (148, 171) microg/L and 7.3 (7.0, 7.6) mg/L, respectively. Cord SF correlated with sTfR (rho=-0.21, P<0.001). In regression analysis, cord SF correlated with smoking and the use of iron supplements during pregnancy (partial r=-0.12 and 0.16; P<0.05 for both). Cord sTfR was associated with first trimester BMI, gestational age, and male sex (partial r=0.30, 0.24, and 0.19, respectively; P<0.01 for all). Cord SF correlated with SF at 6, 12, and 24 mo (rho=0.45, 0.31, and 0.16 respectively; P<0.05 for all). At age 6 mo, 16 of 17 infants with SF <15 mug/L were boys.

CONCLUSIONS

Cessation of smoking and adequate iron prophylaxis during pregnancy may improve iron status in infancy. Cord SF is a predictor of iron status in the first 2 y of life. Boys are at particular risk of low iron status in early infancy.

Iron deficiency and anemia: disparity exists between children in American Samoa and children living within the US

BACKGROUND/OBJECTIVES

Healthy People 2010 emphasizes elimination of health disparity and improvements in anemia and iron deficiency (ID). The study purpose was to (1) determine the prevalence of anemia, ID and ID anemia (IDA) in children living in American Samoa and (2) compare the prevalence to that found in children living in the United States.

SUBJECTS/METHODS

A total of 211 children from American Samoa, aged 1-5 years of age, participated in this cross-sectional study. Prevalence of anemia, ID and IDA were determined and comparison made using data obtained from children living in the United States. Anemia was diagnosed as hemoglobin (Hb) <110.0 g/l, ID as erythrocyte protoporphyrin (EP) >70 mumol/mol heme and IDA as Hb <110.0 g/l and EP >70 mumol/mol heme.

RESULTS

Anemia, ID and IDA prevalence was 33, 70 and 33%, respectively. The results of children from the United States were as follows: anemia, 9%; ID, 10% and IDA, 2%. Within American Samoan children, ID is positively associated with being breastfed <6 months (P<0.05) and anemia and IDA with lower household income (P<0.05; P<0.01). Mean Hb was significantly lower (P<0.001) and mean EP was significantly higher (P<0.001) than those within children living in the United States.

CONCLUSION

To meet Healthy People 2010 goals in children aged 1-2 years, the prevalence of ID in children living in American Samoa would need to decrease from 83 to 5% and in children aged 3-5 years from 59 to 1%. It is critical to ensure that populations within the United States and its territories are provided appropriate resources to promote health and prevent disease.

Comparison of the nutritional values of follow-on formulae available in Italy

If breast milk is not available during complementary feeding, 'follow-on' formula milk ensures a balanced intake of nutrients and is undoubtedly more suitable for infants than cows' milk. Formula milk provides a lower intake of proteins and saturated fats and a higher concentration of polyunsaturated fats, iron and zinc than cows' milk. In particular, delaying the introduction of cows' milk until the end of the first year of life, or even until after the second year, appears to play a fundamental role in the prevention of iron deficiency anaemia. It may also prevent excess weight gain and obesity and the development of immunoallergic symptoms, and may be important for neurobehavioural development. More than 30 varieties of follow-on formula milk are currently available in Italy alone. This review outlines the nutritional differences between breast, formula and cows' milks, and compares different brands of formula milk.

Iron status at 1 and 6 years versus developmental scores at 6 years in a well-nourished affluent population

AIM

To examine the association between iron status at 1 and 6 years with development at 6 years.

METHODS

In a longitudinal study of children (n = 77), iron status was measured at 1 and 6 years and the Icelandic Developmental Inventory, which evaluates children's motor and verbal development, was filled in by mothers near the children's sixth birthday.

RESULTS

Children, iron-deficient at 1 year (n = 10), had lower fine motor development scores at 6 years than non-iron-deficient (n = 56) (46.7 +/- 4.1 vs. 49.3 +/- 2.0; p = 0.011). Fine motor scores were also lower in children with depleted iron stores at 1 year (n = 26) than non-iron-depleted children (n = 40) (48.0 +/- 3.3 vs. 49.5 +/- 1.8; p = 0.045). Multiple regression analyses, with iron status indices at 6 years, showed that mean corpuscular volume along with male gender predicted significantly positively for expression (adj. R(2)= 0.15; p = 0.018; n = 73), while regression analyses, including iron status at 1 and 6 years, showed that haemoglobin at 6 years was positively associated with gross motor (adj. R(2)= 0.05; p = 0.038; n = 63).

CONCLUSIONS

In an affluent society, iron deficiency and depleted iron stores at 1 year may contribute to worse fine motor developmental scores at 6 years, while low mean corpuscular volume and haemoglobin at 6 years might affect subsequent expression and gross motor scores negatively.

Iron status of inner-city African-American infants

The iron status of African-American infants continues to be subject to debate. We characterized the iron status of 198 9-month-old inner-city infants (94% fed iron-fortified formula) using a comprehensive panel of measures and assessing lead and inflammation markers. The proportion with iron deficiency was calculated based on three approaches (> or = 2 abnormal iron measures with or without anemia for MCV model--NHANES II, ferritin model--NHANES III, or Sweden/Honduras study) and a promising new measure-body iron, calculated from ferritin and transferrin receptor (TfR). There were no sex differences for any iron measure. Hb < 110 g/l was observed in 25%; Hb < or = 105 g/l in 10.1%. Free erythrocyte protoporphyrin (FEP) values were elevated without elevated lead concentrations or an inflammatory response: mean FEP = 86.6 microg/dl red blood cells [75.5 micromol/mol heme]; 52.3% were > 80 microg/dl (1.42 micromol/l), almost half of which were accompanied by a second abnormal iron measure. The estimated prevalence of iron deficiency was 14.4, 5.3, and 2.5% for the MCV model, ferritin model, and Sweden/Honduras cutoffs, respectively, and 4.1% for body iron < 0 mg/kg. Regulation of iron storage is immature at < 1 year of age, making estimates of iron deficiency that depend on ferritin, including body iron, suspect in this age period. Thus, the "true" prevalence of iron deficiency could not be established with confidence due to major differences in the results, depending on the guidelines used. Functional indicators of poor iron status in young infants are urgently needed.

Serum transferrin receptor in children: usefulness for determinating the nature of anemia in infection

OBJECTIVES

To know the variations of serum transferrin receptor (sTfR) and its indices depending on the status of body iron and the presence of infection in children, to evaluate their usefulness for recognizing the nature of anemia in infection, and to know the role of erythropoietic activity in these conditions.

DESIGN AND METHODS

Three hundred and sixty-eight children between 1 and 10 years were included: 206 healthy children; 60 iron deficient anemic children (IDA); 102 with anemia and infectious disease, 58 of them meeting criteria for IDA. We measured hemoglobin, red cell indices, reticulocytes, transferrin saturation, serum ferritin, erythrocyte protoporphyrin, serum erythropoietin, and sTfR. Statistic method: ANOVA test, multiple linear regression, and ROC curve.

RESULTS

sTfR, sTfR/ferritin ratio, and sTfR-logferritin index values were found to increase significantly in IDA children. These values were significantly lower in infectious anemia than iron deficiency states. Serum erythropoietin only was elevated significantly in iron deficiency states. In children without infection, mean corpuscular hemoglobin, erythrocyte protoporphirin, erythropoietin logarithm, and total-iron-binding-capacity logarithm predicted 81% of sTfR variability. sTfR and its indices showed a very high sensitivity and specificity for recognizing iron deficiency states. In children with IDA and infection sensitivity for sTfR/ferritin ratio was low (area under the curve: 0.71; 95% confidence interval: 0.64-0.88). For discriminating the nature of anemia in infection the cut-off point obtained for sTfR, sTfR/ferritin ratio, and sTfR-F index were 3, 70, and 1.8, respectively, and their sensitivity and specificity were also very high.

CONCLUSIONS

sTfR, sTfR/ferritin ratio, and sTfR-F index are useful parameters for recognizing iron deficiency and the nature of anemia in infection. In IDA+infection, sTfR/ferritin ratio should not be recommended in the diagnosis of iron deficiency. In iron deficiency, erythropoietic activity has a secondary role as predictor factor of sTfR levels.

Iron deficiency in infancy: applying a physiologic framework for prediction

BACKGROUND

Infants aged 6-24 mo are at high risk of iron deficiency. Numerous studies worldwide have sought to identify predictors of iron deficiency in this age group.

OBJECTIVE

The objectives of the study were to apply a physiologic model to identify risk factors for iron deficiency and to consider those risk factors under different conditions of iron supplementation. We predicted that factors related to iron status at birth (lower gestational age and lower birth weight), postnatal needs for iron (more rapid growth), and bioavailable iron (more cow milk) would be major risk factors.

DESIGN

The physiologic framework was assessed in 1657 Chilean infants (aged 12 mo) with birth weights >or=3 kg who were randomly assigned at age 6 mo to high or low iron supplementation or no added iron. Based on venous blood, the analysis used mean corpuscular volume and concentrations of hemoglobin, free erythrocyte protoporphyrin, and ferritin. Logistic regression models were used to identify predictors of iron deficiency anemia and iron deficiency without anemia.

RESULTS

The prevalence of iron deficiency (>or=2 abnormal iron measures) was 34.9% at age 12 mo. Of 186 infants with hemoglobin concentrations <110 g/L, 158 (84.9%) were iron deficient. The only consistent (and the strongest) predictor of iron deficiency or iron deficiency anemia was lower 6-mo hemoglobin. Factors related to poorer iron status at birth (lower birth weight, shorter gestation though full-term, or both) were predictors in the no-added-iron and high-iron groups. Otherwise, predictors varied by iron supplementation.

CONCLUSION

Variations in predictors of iron deficiency or iron deficiency anemia according to iron supplementation suggest that direct comparisons across studies are tenuous at best without data on early iron status and certainty that specific conditions are comparable.

Partially hydrolyzed guar gum increases intestinal absorption of iron in growing rats with iron deficiency anemia

OBJECTIVE

The objective of this study was to evaluate the effect of partially hydrolyzed guar gum (PHGG) dietary fiber towards intestinal iron absorption, for dietary intake and on the growth of rats with iron deficiency anemia in comparison to those fed on a diet with cellulose and without dietary fiber.

MATERIALS AND METHODS

Male Wistar rats (n=24) weaned at 21 days were fed with AIN93-G diet without iron for 2 weeks in order to induce iron deficiency anemia. At 36 days old, the anemic rats were divided into three groups: (1) PHGG group-100g of PHGG per kg of diet; (2) Cellulose group-100g of cellulose per kg of diet; (3) Control group-diet without dietary fiber. All the diets had 25mg of elemental iron/kg of diet added to lead to recovery from iron deficiency anemia.

RESULTS

The final hemoglobin values in g/dl, for the PHGG group, the cellulose group and the control group were, respectively: 11.3+/-1.2, 8.6+/-0.7 and 8.1+/-0.9 (P<0.001). The levels of hepatic iron, in mug/g of dry tissue, in the same order, were: 322.2+/-66.6, 217.2+/-59.1 and 203.7+/-42.4 (P<0.001). Apparent iron intestinal absorption was, respectively: 67.5+/-8.9%, 35.4+/-15.3% and 31.3+/-24.9% (P<0.001). The three groups consumed similar quantities of diet. The changes in weight and in body length were similar in the three groups studied.

CONCLUSION

PHGG led to greater intestinal absorption of iron, regeneration of hemoglobin and hepatic levels of iron than diet with cellulose and diet control.

Does inadequate maternal iron or DHA status have a negative impact on an infant's functional outcomes?

Marginal intake of iron and omega-3 long-chain fatty acids (DHA) is prevalent among pregnant women. It is not clear to what extent poor iron or DHA status during pregnancy impacts on an infant's functional outcomes. A few studies suggest that inadequate maternal iron or DHA status may be associated with suboptimal functional outcomes in infants. In addition, there is a lack of prospective studies using randomized, double-blind design or experimental studies with appropriate animal models. Although both nutrients are involved in early brain development and their metabolism is interrelated, no study has examined the interaction between iron and omega-3 fatty acids during pregnancy.

CONCLUSION

Long-term studies on large cohorts of pregnant women and their infants are needed to determine whether inadequate iron or DHA status during pregnancy is detrimental to infant neurodevelopment.

A novel method for the filterless preconcentration of iron

A novel method of analysis of iron by filterless preconcentration is presented. This is the first example of efficient preconcentration of a refractory transition metal where coprecipitation and columns were omitted. The method applies a manifold of flow injection analysis (FIA) to iron species that are preconcentrated on the inner walls of a tubular reactor. It was found that the adsorption of iron species to the walls was particularly pronounced in reactors of nylon material and enrichment factors of 30-35 could be attained, as dependent on the length of the reactor and on the time of preconcentration. In the preconcentration step of the FIA accessory, the optimum efficacy was obtained when the acidity of the samples was adjusted by HCl to pH = 2.5 whereas the ammonia preconcentration buffer should be kept alkaline at pH = 9.8. After being preconcentrated on the tubular reactor, the iron species were eluted by hydrochloric acid and analysed by flame atomic absorption spectrometry (FAAS). An unprecedented low limit of detection (LOD, 3sigma) of 1.8 microg L(-1) was thus obtained for the analysis of iron by FAAS, and the calibration line was linear up to 100 microg L(-1). A high sampling frequency of 40 per hour was obtained and the protocol allowed analysis of small amounts of iron in drinking water, in digested samples and in saline water. The major influence of interferences originated from ligands that are known to complex strongly to iron species. The method thus developed was uncomplicated in operation and it exhibited an excellent long-term stability and a high selectivity. Further, it was environmentally safe owing to production of non-toxic waste disposals. Equally high enrichment factors (EF) were obtained for Fe(ii) and Fe(iii), which is explained by the very low solubility product of both species.

Iron status of young Vietnamese children in Australia

OBJECTIVE

The aim of this study was to estimate the prevalence of iron deficiency in Vietnamese children living in Australia and to identify risk factors associated with iron deficiency.

METHODS

A cohort of healthy term Vietnamese infants, were followed from birth (n = 210) to 18 months (n = 174) with anthropometry, dietary intake and feeding practices measured at seven time points. Socio-demographic data were collected from the parents at the first home visit. At 18 months iron status was examined by full blood count and plasma ferritin concentration in 129/152 (85%) of the eligible children. Iron depletion was defined as a plasma ferritin level < 10 microg/L. Iron deficiency without anaemia was defined as iron depletion plus MCV < 70fl and iron deficiency anaemia was defined as iron deficiency anaemia plus Hb < 110 g/L.

RESULTS

The prevalence of iron deficiency was iron depletion 19.4% (95% CI: 13.0%, 27.3%), iron deficiency without anaemia 3.1% (95% CI: 0.9%, 7.8%) and iron deficiency anaemia 3.9% (95% CI: 1.3%, 8.8%). Multiple regression analysis showed three significant predictors of iron deficiency: cows milk intake (negative effect), meat, fish or poultry intake (positive effect) and weight gain (negative effect). A cows milk intake > or = 650 mL/day was a risk factor for iron deficiency.

CONCLUSION

Prevalence of iron deficiency at 18 months was high despite appropriate infant feeding practices during the first year. Modification of the diet in the second year of life may decrease the risk of iron deficiency in Vietnamese children.

Dietary iron intake is positively associated with hemoglobin concentration during infancy but not during the second year of life

Iron status during infancy and early childhood reflects highly dynamic processes, which are affected by both internal and external factors. The regulation of iron metabolism seems to be subjected to developmental changes during infancy, although the exact nature of these changes and their implications are not fully understood. We wanted to explore the association between dietary iron intake and indicators of iron status, and to assess temporal changes in these variables. This was done by secondary analysis of data from a recently conducted dietary intervention trial in which healthy, term, well-nourished infants were randomly assigned to consume iron-fortified infant cereals with regular or low phytate content, or iron-fortified infant formula. Dietary iron intake from 6 to 8 mo and from 9 to 11 mo was associated with hemoglobin (Hb) concentration at 9 mo (r = 0.27, P < 0.001) and 12 mo (r = 0.21, P = 0.001), respectively, but iron intake from 12 to 18 mo was not associated with Hb at 18 mo. In contrast, iron intake from 6 to 11 mo was not associated with serum ferritin (S-Ft) at 9 or 12 mo, whereas iron intake from 12 to 17 mo was positively associated with S-Ft at 18 mo (r = 0.14, P = 0.032). These shifts in associations between dietary iron intake, and Hb and S-Ft, respectively, may be due to developmental changes in the channeling of dietary iron to erythropoiesis relative to storage, in the absence of iron deficiency anemia. These observations should be taken into consideration when evaluating iron nutritional status during infancy and early childhood.

Iron deficiency and iron deficiency anaemia during infancy and childhood

The present definition of iron deficiency and iron deficiency anaemia is under debate. Our present figures for the prevalence of iron deficiency in infants and toddlers are thus disputed.

CONCLUSION

Better understanding of the regulation of iron metabolism and requirement during the critical early period of growth and development is needed for relevant control of iron deficiency anaemia.

Nutrition in the 21st century: what is going wrong

"Things sweet to taste prove in digestion sour" (Shakespeare, Richard II, Act 1, Scene 3, line 236)

Iron deficiency and risk factors for lower iron stores in 6–24-month-old New Zealanders

OBJECTIVES

To determine the prevalence of biochemical iron deficiency and identify factors associated with ferritin levels among 6-24-month-old urban South Island New Zealand children.

DESIGN

Cross-sectional survey conducted from May 1998 to March 1999.

SETTING

The cities of Christchurch, Dunedin and Invercargill.

SUBJECTS

A total of 323 randomly selected 6-24-month-old children participated (response rate 61%) of which 263 provided a blood sample.

METHODS

A complete blood cell count, zinc protoporphyrin, serum ferritin and C-reactive protein were measured on nonfasting venipuncture blood samples, 3-day weighed food records and general questionnaire data were collected.

RESULTS

Among children with C-reactive protein<10 mg/l (n=231), 4.3% had iron deficiency anaemia, 5.6% had iron deficiency without anaemia, and 18.6% had depleted iron stores, when a ferritin cutoff of < or =12 g/l was used. Age (negative), sex (girls>boys), ethnicity (Caucasian>non-Caucasian), weight-for-age percentiles (negative) and birth weight (positive) were associated with ferritin after adjusting for infection and socioeconomic status. When current consumption of iron fortified formula and >500 ml of cows' milk per day were included, these were associated with a 22% increase and 25% decrease in ferritin, respectively (R2=0.28).

CONCLUSIONS

The presence of suboptimal iron status (29%) among young New Zealand children is cause for concern, even though severe iron deficiency is rare, because children with marginal iron status are at risk of developing severe iron deficiency if exposed to a physiological challenge.

A double-masked, randomized control trial of iron supplementation in early infancy in healthy term breast-fed infants

OBJECTIVES

To test whether iron supplementation affects hematologic, biochemical, and developmental status in term breast-fed infants.

STUDY DESIGN

Term breast-fed infants (n=77) were randomly selected to receive either 7.5 mg per day of elemental iron as ferrous sulfate or placebo from 1 to 6 months of age. Investigators and families were unaware of group assignment. Complete blood count and ferritin, red cell superoxide dismutase, catalase, plasma ferric reducing antioxidant power, and zinc and copper levels were analyzed at 1, 3.5, 6, and 12 months of age. Bayley mental and psychomotor developmental indexes (MDI and PDI) and visual acuity (with the use of Teller acuity cards) were assessed from 12 to 18 months of age. Analysis performed by analysis of variance and t tests was by intention to treat.

RESULTS

Iron supplementation resulted in higher hemoglobin and mean corpuscular volume at 6 months of age and significantly higher visual acuity and PDI at 13 months of age (100+/-12 vs 93+/-9 [+/-SD]). Treatment and placebo groups did not differ in anthropometric indexes, compliance, biochemical status, or demographic characteristics.

CONCLUSIONS

Iron supplementation of breast-fed infants appears safe and might have beneficial hematologic and developmental effects for some infants.

Effects of weaning cereals with different phytate contents on hemoglobin, iron stores, and serum zinc: a randomized intervention in infants from 6 to 12 mo of age

BACKGROUND

Weaning foods frequently contain phytate, an inhibitor of iron and zinc absorption, which may contribute to the high prevalence of iron and zinc deficiency seen in infancy.

OBJECTIVE

The objective was to investigate whether either an extensive reduction in the phytate content of infant cereals or the use of milk-based, iron-fortified infant formula would improve iron and zinc status in infants.

DESIGN

In a double-blind design, infants (n = 300) were randomly assigned to 3 cereal groups from 6 to 12 mo of age: commercial milk-based cereal drink (MCD) and porridge (CC group), phytate-reduced MCD and phytate-reduced porridge (PR group), or milk-based infant formula and porridge with the usual phytate content (IF group). Venous blood samples were collected at 6 and 12 mo. Dietary intake was recorded monthly. After the intervention, 267 infants remained in the analysis.

RESULTS

Hemoglobin concentrations of < 110 g/L, serum ferritin concentrations of < 12 microg/L, and serum zinc concentrations of < 10.7 micromol/L had overall prevalences at baseline and 12 mo of 28% and 15%, 9% and 18%, and 22% and 27%, respectively. After the intervention, there were no significant differences in any measure of iron or zinc status between the CC and the PR groups. However, hemoglobin was significantly higher (120 g/L compared with 117 g/L; P = 0.012) and the prevalence of anemia was lower (13% compared with 23%; P = 0.06) in the PR group than in the IF group, which could be explained by differences in daily iron intake between the 2 groups.

CONCLUSION

Extensive reduction in the phytate content of weaning cereals had little long-term effect on the iron and zinc status of Swedish infants.

The diagnostic criteria for iron deficiency in infants should be reevaluated

Diagnostic criteria for iron deficiency (ID) and iron deficiency anemia (IDA) in infants are poorly defined. Our aim was to establish appropriate cut-off values for hemoglobin (Hb), plasma ferritin, erythrocyte mean cell volume (MCV), zinc protoporphyrin (ZPP) and soluble transferrin receptors (TfR) in infancy. Exclusively breast-fed infants (n = 263) in Honduras and Sweden were randomly assigned to receive iron supplementation or placebo, and blood samples were obtained at 4, 6 and 9 mo of age. Reference ranges were determined using three different approaches for defining iron-replete infants. The usefulness of several variables for predicting the Hb response to iron was evaluated. We found the following 2 SD cut-off values in iron-replete infants: Hb <105 g/L at 4-6 mo and <100 g/L at 9 mo; ZPP >75 micro mol/mol heme at 4-6 mo and >90 micro mol/mol heme at 9 mo; ferritin <20 micro g/L at 4 mo, <9 micro g/L at 6 mo and <5 micro g/L at 9 mo; and TfR >11 mg/L at 4-9 mo. The Hb response to iron was not a useful definition of IDA at 4 mo of age. Hb, MCV and ZPP at 6 mo as well as growth variables predicted the Hb response at 6-9 mo, but ferritin and TfR at 6 mo did not. We conclude that there is need for a reevaluation of the definitions of ID and IDA in infants.