Rapid growth is a dominant predictor of hepcidin suppression and declining ferritin in Gambian infants

Calcium and Iron Nutrition through the Reproductive Life Course

BACKGROUND

Two essential micronutrients over the life course are calcium and iron, and both are especially important during the reproductive cycle. The role of calcium in maternal and offspring bone health and in the prevention of pre-eclampsia in pregnancy are well described, although results from randomised controlled trials for both outcomes vary. Iron is essential for synthesis of red blood cells, being a core component of haemoglobin, which carries oxygen around the body, and hence is key in the prevention of anaemia and sequelae.

SUMMARY

This article reviews the evidence across the reproductive life course for dietary calcium and iron intakes and health outcomes. For calcium, focusing on bone health and prevention of pre-eclampsia, for iron considering its crucial role in foetal and neonatal development and how requirements may be impacted through inflammation and infection, particularly in environments where iron availability may be low.

The effect of iron supplementation in preterm infants at different gestational ages

BACKGROUND

Iron deficiency (ID) is the most prevalent nutritional deficiency disease in preterm infants, significantly affecting their growth and development. For preterm infants to flourish physically and neurologically, timely iron supplementation is essential. The main goals of this study were to determine whether the present iron supplementation regimen results in iron overload in late preterm infants and whether it can meet the growth requirements of early preterm infants for catch-up.

METHODS

We conducted a prospective follow-up study on preterm infants at the Department of Child Health, West China Second University Hospital, Sichuan University, from January 1, 2020, to August 31, 2020. In this study, 177 preterm infants were divided into two groups based on gestational age-early preterm infants (gestational age < 34 weeks) and late preterm infants (gestational age ≥ 34 weeks and < 37 weeks)-to compare the incidence of iron deficiency, iron status, and physical growth of preterm infants receiving iron supplements (2-4 mg/kg/d).

RESULTS

Iron supplementation considerably reduced the incidence of iron deficiency in preterm infants. The prevalence of iron deficiency in early preterm infants and late preterm infants was 11.3% and 5.1%, respectively, at the corrected gestational age of 3 months; at the corrected gestational age of 6 months, the prevalence was 5.3% and 6.3%, respectively. No preterm infants with iron deficiency were detected in either group at the corrected gestational age of 12 months. Ferritin was substantially lower in early preterm infants (36.87 ± 31.57 ng/ml) than in late preterm infants (65.78 ± 75.76 ng/ml) at the corrected gestational age of 3 months (p < 0.05). A multifactorial regression analysis of factors influencing iron metabolism levels in preterm infants revealed a positive relationship between log10hepcidin, birth weight, and ferritin, with higher birth weights resulting in higher ferritin levels.

CONCLUSIONS

Postnatal iron supplementation at 2-4 mg/kg/d in preterm infants significantly decreases the incidence of ID. There were substantial differences in iron levels across preterm infants of varying gestational ages. A tailored iron supplementation plan based on growth, birth weight, and gestational age may be a more suitable route for iron supplementation. Although the current study found that the postnatal iron status of early preterm infants differed from that of late preterm infants, the actual mechanism of action remains unknown, and large-sample, multicenter clinical studies are required to investigate this further.

Effects of Iron Status on Adaptive Immunity and Vaccine Efficacy: A Review

Vaccines can prevent infectious diseases, but their efficacy varies, and factors impacting vaccine effectiveness remain unclear. Iron deficiency is the most common nutrient deficiency, affecting >2 billion individuals. It is particularly common in areas with high infectious disease burden and in groups that are routinely vaccinated, such as infants, pregnant women, and the elderly. Recent evidence suggests that iron deficiency and low serum iron (hypoferremia) not only cause anemia but also may impair adaptive immunity and vaccine efficacy. A report of human immunodeficiency caused by defective iron transport underscored the necessity of iron for adaptive immune responses and spurred research in this area. Sufficient iron is essential for optimal production of plasmablasts and IgG responses by human B-cells in vitro and in vivo. The increased metabolism of activated lymphocytes depends on the high-iron acquisition, and hypoferremia, especially when occurring during lymphocyte expansion, adversely affects multiple facets of adaptive immunity, and may lead to prolonged inhibition of T-cell memory. In mice, hypoferremia suppresses the adaptive immune response to influenza infection, resulting in more severe pulmonary disease. In African infants, anemia and/or iron deficiency at the time of vaccination predict decreased response to diphtheria, pertussis, and pneumococcal vaccines, and response to measles vaccine may be increased by iron supplementation. In this review, we examine the emerging evidence that iron deficiency may limit adaptive immunity and vaccine responses. We discuss the molecular mechanisms and evidence from animal and human studies, highlight important unknowns, and propose a framework of key research questions to better understand iron-vaccine interactions.

Early iron supplementation in exclusively breastfed Gambian infants: a randomized controlled trial

Objective

To investigate the effect of daily iron supplementation for 14 weeks on the serum iron concentration and other markers of iron status in exclusively breastfed infants in Gambia.

Methods

A placebo-controlled, randomized, double-blind trial was performed in rural Gambia between 3 August 2021 and 9 March 2022. Overall, 101 healthy, exclusively breastfed infants aged 6 to 10 weeks were recruited at vaccination clinics and through community health workers. Infants were randomized to receive iron supplementation (7.5 mg/day as ferrous sulfate in sorbitol solution) or placebo for 98 days. Venous blood samples were collected at baseline and on day 99 to assess the serum iron concentration and other markers of iron and haematological status.

Findings

At day 99, the serum iron concentration was significantly higher in the iron supplementation group than the placebo group (crude difference in means: 2.5 µmol/L; 95% confidence interval: 0.6 to 4.3) and there were significant improvements in other iron and haematological markers. There were 10 serious adverse events (five in each group), 106 non-serious adverse events (54 with iron supplementation; 52 with placebo) and no deaths. There was no marked difference between the groups in maternally reported episodes of diarrhoea, fever, cough, skin infection, eye infection or nasal discharge.

Conclusion

In exclusively breastfed Gambian infants, iron supplementation from 6 weeks of age was associated with a significant improvement in markers of iron status at around 6 months of age. There was no indication of adverse effects on growth or infections.

Iron deficiency in healthy, term infants aged five months, in a pediatric outpatient clinic: a prospective study

BACKGROUND

Iron deficiency (ID) is prevalent in Malaysian children. The incidence of ID in infants under 6 months of age is unknown. Our aim was to determine the prevalence of iron deficiency (ID) and iron deficiency anemia (IDA) in healthy, term infants aged below 6 months in our hospital population.

METHODS

A prospective longitudinal pilot study of mother-infant pairs was conducted on infants receiving routine immunizations in a mother and child clinic at a university hospital, in Kuala Lumpur, Malaysia. Mothers completed standardized questionnaires at 3- and 5-month postnatal visits. Maternal and infant full blood count, ferritin, and C-reactive protein (CRP) levels were measured at 3 months and for the infants repeated at 5 months. Infant anthropometric measurements were obtained at both visits. We conducted a univariate analysis to identify factors associated with ID and IDA.

RESULTS

Altogether, 91 mother-infant pairs were enrolled, with 88 completing the study. No infant had ID or IDA at 3 months; the lowest ferritin level was 16.6 µg/L. At 5 months, 5.9% (5/85) of infants had ID, and 2.4% (2/85) had IDA. Median (interquartile range) infant ferritin levels significantly declined from 113.4 (65.0-183.6) µg/L at 3 months to 50.9 (29.2-70.4) µg/L at 5 months, p < 0.001. Exclusive breastfeeding until 3 or 5 months was significantly associated with ID at 5 months (p = 0.020, and p = 0.008, respectively) on univariate analysis. The drop in ferritin between 3-5 months was significantly associated with weight and length gains between 0-3 months (p = 0.018, p = 0.009, respectively). Altogether, 14.3% of infants exclusively breastfed until 5 months developed ID. At 5 months, 3.4% of infants were underweight, 1.1% stunted, and 10.2% wasted.

CONCLUSIONS

In exclusively breastfed term infants, ID occurred by 5 months. Early introduction of iron-rich foods should be considered in exclusively breastfed babies. A high prevalence of wasting suggests a calorie deficit in this population and will lead to stunting if not addressed.

Biology of Anemia: A Public Health Perspective

Our goal is to present recent progress in understanding the biological mechanisms underlying anemia from a public health perspective. We describe important advances in understanding common causes of anemia and their interactions, including iron deficiency (ID), lack of other micronutrients, infection, inflammation, and genetic conditions. ID develops if the iron circulating in the blood cannot provide the amounts required for red blood cell production and tissue needs. ID anemia develops as iron-limited red blood cell production fails to maintain the hemoglobin concentration above the threshold used to define anemia. Globally, absolute ID (absent or reduced body iron stores that do not meet the need for iron of an individual but may respond to iron supplementation) contributes to only a limited proportion of anemia. Functional ID (adequate or increased iron stores that cannot meet the need for iron because of the effects of infection or inflammation and does not respond to iron supplementation) is frequently responsible for anemia in low- and middle-income countries. Absolute and functional ID may coexist. We highlight continued improvement in understanding the roles of infections and inflammation in causing a large proportion of anemia. Deficiencies of nutrients other than iron are less common but important in some settings. The importance of genetic conditions as causes of anemia depends upon the specific inherited red blood cell abnormalities and their prevalence in the settings examined. From a public health perspective, each setting has a distinctive composition of components underlying the common causes of anemia. We emphasize the coincidence between regions with a high prevalence of anemia attributed to ID (both absolute and functional), those with endemic infections, and those with widespread genetic conditions affecting red blood cells, especially in sub-Saharan Africa and regions in Asia and Oceania.

Weak response of bovine hepcidin induction to iron through decreased expression of Smad4

Hepcidin negatively regulates systemic iron levels by inhibiting iron entry into the circulation. Hepcidin production is increased in response to an increase in systemic iron via the activation of the bone morphogenetic protein (BMP) pathway. Regulation of hepcidin expression by iron status has been proposed on the basis of evidence mainly from rodents and humans. We evaluated the effect of iron administration on plasma hepcidin concentrations in calves and the expression of bovine hepcidin by the BMP pathway in a cell culture study. Hematocrit as well as levels of blood hemoglobin and plasma iron were lower than the reference level in calves aged 1-4 weeks. Although intramuscular administration of iron increased iron-related parameters, plasma hepcidin concentrations were unaffected. Treatment with BMP6 increased hepcidin expression in human liver-derived cells but not in bovine liver-derived cells. A luciferase-based reporter assay revealed that Smad4 was required for hepcidin reporter transcription induced by Smad1. The reporter activity of hepcidin was lower in the cells transfected with bovine Smad4 than in those transfected with murine Smad4. The lower expression levels of bovine Smad4 were responsible for the lower activity of the hepcidin reporter, which might be due to the instability of bovine Smad4 mRNA. In fact, the endogenous Smad4 protein levels were lower in bovine cells than in human and murine cells. Smad4 also confers TGF-β/activin-mediated signaling. Induction of TGF-β-responsive genes was also lower after treatment with TGF-β1 in bovine hepatocytes than in human hepatoma cells. We revealed the unique regulation of bovine hepcidin expression and the characteristic TGF-β family signaling mediated by bovine Smad4. The present study suggests that knowledge of the regulatory expression of hepcidin as well as TGF-β family signaling obtained in murine and human cells is not always applicable to bovine cells.

Iron status in early infancy is associated with trajectories of cognitive development up to pre-school age in rural Gambia

INTRODUCTION

Iron deficiency is among the leading risk factors for poor cognitive development. However, interventions targeting iron deficiency have had mixed results on cognitive outcomes. This may be due to previous interventions focusing on the correction of iron deficiency anaemia in late infancy and early childhood, at which point long lasting neural impacts may already be established. We hypothesise that the relationship between iron status and cognitive development will be observable in the first months of life and will not be recovered by 5 years of age.

METHODS

Using data from the Brain Imaging for Global Health (BRIGHT) Study in Gambia (n = 179), we conducted mixed effects modelling to assess the relationship between iron status at 5 months of age and trajectories of cognitive development from 5 months- 5 years using (i) a standardised measure of cognitive development (Mullen Scales of Early Learning) and (ii) an eye-tracking assessment of attention processing (visual disengagement time).

RESULTS

All infants were iron sufficient at 1 month of age. At 5 and 12 months of age 30% and 55% of infants were iron deficient respectively. In fully adjusted analyses, infants in the lowest tercile of soluble transferrin receptor (sTfR) (best iron status) achieved MSEL Cognitive Scores on average 1.9 points higher than infants in the highest sTfR tercile (p = 0.009, effect size = 0.48). There was no evidence that this group difference was recovered by 5 years of age. Infants in the lowest sTfR tercile had visual disengagement time 57ms faster than the highest tercile (p = 0.001, effect size = 0.59). However, this difference diminished by early childhood (p = 0.024).

CONCLUSION

Infants are at risk of iron deficiency in early infancy. A relationship between iron status and cognitive development is apparent from 5 months of age and remains observable at 5 years of age. One mechanism by which iron availability in early infancy impacts brain development may be through effects on early attentional processing, which is rapidly developing and has substantial nutritional requirements during this period. To support neurocognitive development, prevention of iron deficiency in pre- and early postnatal life may be more effective than correcting iron deficiency once already established.

Cellular iron governs the host response to malaria

Malaria and iron deficiency are major global health problems with extensive epidemiological overlap. Iron deficiency-induced anaemia can protect the host from malaria by limiting parasite growth. On the other hand, iron deficiency can significantly disrupt immune cell function. However, the impact of host cell iron scarcity beyond anaemia remains elusive in malaria. To address this, we employed a transgenic mouse model carrying a mutation in the transferrin receptor (TfrcY20H/Y20H), which limits the ability of cells to internalise iron from plasma. At homeostasis TfrcY20H/Y20H mice appear healthy and are not anaemic. However, TfrcY20H/Y20H mice infected with Plasmodium chabaudi chabaudi AS showed significantly higher peak parasitaemia and body weight loss. We found that TfrcY20H/Y20H mice displayed a similar trajectory of malaria-induced anaemia as wild-type mice, and elevated circulating iron did not increase peak parasitaemia. Instead, P. chabaudi infected TfrcY20H/Y20H mice had an impaired innate and adaptive immune response, marked by decreased cell proliferation and cytokine production. Moreover, we demonstrated that these immune cell impairments were cell-intrinsic, as ex vivo iron supplementation fully recovered CD4+ T cell and B cell function. Despite the inhibited immune response and increased parasitaemia, TfrcY20H/Y20H mice displayed mitigated liver damage, characterised by decreased parasite sequestration in the liver and an attenuated hepatic immune response. Together, these results show that host cell iron scarcity inhibits the immune response but prevents excessive hepatic tissue damage during malaria infection. These divergent effects shed light on the role of iron in the complex balance between protection and pathology in malaria.

Universal iron supplementation: the best strategy to tackle childhood anaemia in malaria-endemic countries?

Iron deficiency presents a major public health concern in many malaria-endemic regions, and both conditions affect young children most severely. Daily iron supplementation is the standard public health intervention recommended to alleviate rates of iron deficiency in children, but there is controversy over whether universal supplementation could increase the incidence and severity of malaria infection. Current evidence suggests that iron supplementation of deficient individuals is safe and effective in high-transmission settings when accompanied by malaria prevention strategies. However, low-resource settings often struggle to effectively control the spread of malaria, and it remains unclear whether supplementation of iron replete individuals could increase their risk of malaria and other infections. This review explores the evidence for and against universal iron supplementation programmes, and alternative strategies that could be used to alleviate iron deficiency in malaria-endemic areas, while minimising potential harm.

Iron homeostasis in full-term, normal birthweight Gambian neonates over the first week of life

Human neonates elicit a profound hypoferremia which may protect against bacterial sepsis. We examined the transience of this hypoferremia by measuring iron and its chaperone proteins, inflammatory and haematological parameters over the first post-partum week. We prospectively studied term, normal weight Gambian newborns. Umbilical cord vein and artery, and serial venous blood samples up to day 7 were collected. Hepcidin, serum iron, transferrin, transferrin saturation, haptoglobin, c-reactive protein, α1-acid-glycoprotein, soluble transferrin receptor, ferritin, unbound iron-binding capacity and full blood count were assayed. In 278 neonates we confirmed the profound early postnatal decrease in serum iron (22.7 ± 7.0 µmol/L at birth to 7.3 ± 4.6 µmol/L during the first 6-24 h after birth) and transferrin saturation (50.2 ± 16.7% to 14.4 ± 6.1%). Both variables increased steadily to reach 16.5 ± 3.9 µmol/L and 36.6 ± 9.2% at day 7. Hepcidin increased rapidly during the first 24 h of life (19.4 ± 14.4 ng/ml to 38.9 ± 23.9 ng/ml) and then dipped (32.7 ± 18.4 ng/ml) before rising again at one week after birth (45.2 ± 19.1 ng/ml). Inflammatory markers increased during the first week of life. The acute postnatal hypoferremia in human neonates on the first day of life is highly reproducible but transient. The rise in serum iron during the first week of life occurs despite very high hepcidin levels indicating partial hepcidin resistance.Trial Registration: clinicaltrials.gov (NCT03353051). Registration date: November 27, 2017.

Regulation of iron absorption in infants

BACKGROUND

Iron programs in low- and middle-income countries often target infants and young children. Limited data from human infants and mouse models suggest that homeostatic control of iron absorption is incomplete in early infancy. Excess iron absorption during infancy may have detrimental effects.

OBJECTIVES

Our aims were to 1) investigate determinants of iron absorption in infants aged 3-15 mo and assess whether regulation of iron absorption is fully mature during this period and 2) define the threshold ferritin and hepcidin concentrations in infancy that trigger upregulation of iron absorption.

METHODS

We performed a pooled analysis of standardized, stable iron isotope absorption studies performed by our laboratory in infants and toddlers. We used generalized additive mixed modeling (GAMM) to examine relationships between ferritin, hepcidin, and fractional iron absorption (FIA).

RESULTS

Kenyan and Thai infants aged 2.9-15.1 mo (n = 269) were included; 66.8% were iron deficient and 50.4% were anemic. In regression models, hepcidin, ferritin, and serum transferrin receptor were significant predictors of FIA, whereas C-reactive protein was not. In the model including hepcidin, hepcidin was the strongest predictor of FIA (β = -0.435). In all models, interaction terms, including age, were not significant predictors of FIA or hepcidin. The fitted GAMM trend of ferritin versus FIA showed a significant negative slope until ferritin of 46.3 μg/L (95% CI: 42.1, 50.5 μg/L), which corresponded to an FIA decrease from 26.5% to 8.3%; above this ferritin value, FIA remained stable. The fitted GAMM trend of hepcidin versus FIA showed a significant negative slope until hepcidin of 3.15 nmol/L (95% CI: 2.67, 3.63 nmol/L), above which FIA remained stable.

CONCLUSIONS

Our findings suggest that the regulatory pathways of iron absorption are intact in infancy. In infants, iron absorption begins to increase at threshold ferritin and hepcidin values of ∼46 μg/L and ∼3 nmol/L, respectively, similar to adult values.

Acknowledging the gap: a systematic review of micronutrient supplementation in infants under six months of age

Background: Micronutrient deficiencies remain common worldwide, but the consequences to growth and development in early infancy (under six months of age) are not fully understood. We present a systematic review of micronutrient interventions in term infants under six months of age, with a specific focus on iron supplementation. Methods: We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid) and Embase (Ovid) from January 1980 through December 2019. Interventions included iron or multiple micronutrients (MMNs). Results: Of 11,109 records identified, 33 publications from 24 trials were included (19 iron and five MMN supplementation trials). All but one trial (evaluating only morbidity and mortality) evaluated the effect of supplementation on biochemical outcomes, ten reported on growth, 15 on morbidity and/or mortality and six on neuro-behavioural development. Low- and middle- income countries made up 88% (22/25) of the total trial locations. Meta-analysis was not possible due to extensive heterogeneity in both exposure and outcome measures.  However, these trials indicated that infants less than six months of age benefit biochemically from early supplementation with iron, but the effect of additional nutrients or MMNs, along with the impacts on growth, morbidity and/or mortality, and neuro-behavioural outcomes remain unclear. Conclusions: Infants less than six months of age appear to benefit biochemically from micronutrient supplementation. However, well-powered randomised controlled trials are required to determine whether routine supplementation with iron or MMNs containing iron should commence before six months of life in exclusively breast-fed infants in low-resource settings.

Acknowledging the gap: a systematic review of micronutrient supplementation in infants under six months of age

Background: Micronutrient deficiencies remain common worldwide, but the consequences to growth and development in early infancy (under six months of age) are not fully understood. We present a systematic review of micronutrient interventions in term infants under six months of age, with a specific focus on iron supplementation. Methods: We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid) and Embase (Ovid) from January 1980 through December 2019. Interventions included iron or multiple micronutrients (MMNs). Results: Of 11,109 records identified, 32 publications from 23 trials were included (18 iron and five MMN supplementation trials). All 23 trials evaluated the effect of supplementation on biochemical outcomes, ten reported on growth, 14 on morbidity and/or mortality and six on neuro-behavioural development. Low- and middle- income countries made up 88% (21/24) of the total trial locations. Meta-analysis was not possible due to extensive heterogeneity in both exposure and outcome measures.  However, these trials indicated that infants less than six months of age benefit biochemically from early supplementation with iron, but the effect of additional nutrients or MMNs, along with the impacts on growth, morbidity and/or mortality, and neuro-behavioural outcomes remain unclear. Conclusions: Infants less than six months of age appear to benefit biochemically from micronutrient supplementation. However, well-powered randomised controlled trials are required to determine whether routine supplementation with iron or MMNs containing iron should commence before six months of life in exclusively breast-fed infants in low-resource settings.

Effects of iron deficiency and iron supplementation at the host-microbiota interface: Could a piglet model unravel complexities of the underlying mechanisms?

Iron deficiency is the most prevalent human micronutrient deficiency, disrupting the physiological development of millions of infants and children. Oral iron supplementation is used to address iron-deficiency anemia and reduce associated stunting but can promote infection risk since restriction of iron availability serves as an innate immune mechanism against invading pathogens. Raised iron availability is associated with an increase in enteric pathogens, especially Enterobacteriaceae species, accompanied by reductions in beneficial bacteria such as Bifidobacteria and lactobacilli and may skew the pattern of gut microbiota development. Since the gut microbiota is the primary driver of immune development, deviations from normal patterns of bacterial succession in early life can have long-term implications for immune functionality. There is a paucity of knowledge regarding how both iron deficiency and luminal iron availability affect gut microbiota development, or the subsequent impact on immunity, which are likely to be contributors to the increased risk of infection. Piglets are naturally iron deficient. This is largely due to their low iron endowments at birth (primarily due to large litter sizes), and their rapid growth combined with the low iron levels in sow milk. Thus, piglets consistently become iron deficient within days of birth which rapidly progresses to anemia in the absence of iron supplementation. Moreover, like humans, pigs are omnivorous and share many characteristics of human gut physiology, microbiota and immunity. In addition, their precocial nature permits early maternal separation, individual housing, and tight control of nutritional intake. Here, we highlight the advantages of piglets as valuable and highly relevant models for human infants in promoting understanding of how early iron status impacts physiological development. We also indicate how piglets offer potential to unravel the complexities of microbiota-immune responses during iron deficiency and in response to iron supplementation, and the link between these and increased risk of infectious disease.

Trace Element Interactions, Inflammatory Signaling, and Male Sex Implicated in Reduced Growth Following Excess Oral Iron Supplementation in Pre-Weanling Rats

Iron supplements are frequently provided to infants in high-income countries despite low incidence of iron deficiency. There is growing concern regarding adverse health and development outcomes of excess iron provision in early life. Excess iron may directly damage developing organs through the formation of reactive oxygen species, alter systemic inflammatory signaling, and/or dysregulate trace mineral metabolism. To better characterize the in vivo effects of excess iron on development, we utilized a pre-weanling rat pup model. Lewis rat litters were culled to eight pups (four males and four females) and randomly assigned to daily supplementation groups receiving either vehicle control (CON; 10% w/v sucrose solution) or ferrous sulfate (FS) iron at one of the following doses: 10, 30, or 90 mg iron/kg body weight—FS-10, FS-30, and FS-90, respectively—from postnatal day (PD) 2 through 9. FS-90 litters, but not FS-30 or FS-10, failed to thrive compared to CON litters and had smaller brains on PD 10. Among the groups, FS-90 liver iron levels were highest, as were white blood cell counts. Compared to CON, circulating MCP-1 and liver zinc were increased in FS-90 pups, whereas liver copper was decreased. Growth defects due to excess FS provision in pre-weanling rats may be related to liver injury, inflammation, and altered trace mineral metabolism.

Child linear growth trajectories during the first three years of life in relation to infant iron status: a prospective cohort study in rural Vietnam

Background

Early childhood growth patterns have long-term consequences for health and disease. Little is known about the interplay between growth and iron status during childhood. We explored the interplay between linear growth and iron status during early childhood, by assessing child growth trajectories between 6 and 36 months (m) of age in relation to infant iron status at 6 months of age.

Methods

A cohort study of infants born to women who had previously participated in a cluster randomized controlled trial of antenatal micronutrient supplementation, conducted in rural Vietnam. The relationship between child linear growth trajectories and infant iron status (ferritin concentration) was examined using latent growth curve modeling. Primary outcomes were height for age z scores (HAZ) and growth trajectory between 6 and 36 m of age.

Results

A total of 1112 infants were included in the study. Mean [SD] HAZ scores decreased over time from –0·58 [0·94] at 6 m, to –0·97 [0·99] at 18 m, to –1·14 [0·89] at 36 m of age. There was a steep linear decline in the HAZ scores between 6 and 18 m of age, followed by a slower linear decline from 18 to 36 m of age. Ferritin concentration at 6 m of age was inversely associated with HAZ score at 6 m of age (-0·145, 95% CI [-0.189, -0.101]). There was no association between infant ferritin at 6 m of age and child growth trajectory between 6 and 36 m of age.

Conclusions

Iron status at six months of age did not influence a child’s later linear growth trajectory in this cohort of rural Vietnamese children. Longitudinal studies with repeated ferritin and height measurements are required to better delineate this relationship and inform public health interventions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40795-022-00505-y.

Iron supplementation of breastfed Gambian infants from 6 weeks to 6 months of age: protocol for a randomised controlled trial

Background: A recent analysis showed that plasma iron concentrations decline rapidly from birth in Gambian infants, irrespective of sex or birthweight, to concentrations well below normal expected values for iron-replete children older than two months of age (typically >10 μmol/L). The development and function of neural and immune cells may thus be compromised before the minimum age at which children should receive iron supplementation as per World Health Organisation recommendations. Methods: This study is a two-arm, double-blind, placebo-controlled, randomised superiority trial. Infants will be randomised to receive iron drops (7.5mg/day of iron as ferrous sulphate) or placebo daily for 98 days, to test the impact on serum iron concentrations in healthy, breastfed infants (n = 100) aged 6-10 weeks at enrolment. Participants will be visited daily and supplemented by the field team. Daily health and weekly breastfeeding questionnaires will be administered. Anthropometry, and venous blood and faecal samples will be collected at enrolment and after 98 days of supplementation with serum iron as the primary endpoint. Low birthweight (less than 2.5kg at birth) and infants born prematurely (< 37 weeks) will not be excluded. Formula-fed and infants with any illness will be excluded. An additional study exploring maternal stakeholder perspectives of the intervention will be conducted by means of maternal interviews and four focus group discussions with local stakeholders. Discussion: Most breast-fed Gambian infants have very low circulating iron levels by five months of age. This study will introduce iron supplements much earlier in infancy than has previously been attempted in a low-income setting with the primary aim of increasing serum iron concentration. Trial registration: Clincaltrials.gov ( NCT04751994); 12 th February 2021.

Serum erythroferrone levels during the first month of life in premature infants

OBJECTIVE

To examine erythroferrone (ERFE)-hepcidin iron regulation in premature infants under intensive care at risk of iron metabolic disorders.

STUDY DESIGN

A retrospective cohort recruited 31 infants with a birth weight of <1500 g hospitalized in a tertiary center. Their hematological status was measured at birth and 2 and 4 weeks of life.

RESULTS

ERFE was positively correlated with the reticulocyte hemoglobin content at 2 (r² = 0.2374) and 4 weeks (r² = 0.6005). An assumed negative correlation between ERFE and hepcidin was not determined during the neonatal period. Hepcidin was positively correlated with the leukocyte count (r² = 0.3089) and ferritin (r² = 0.7476) at birth and C-reactive protein (r² = 0.3591) at 2 weeks and negatively correlated with the reticulocyte count (r² = 0.2887) at 4 weeks.

CONCLUSION

The vulnerability of the ERFE-hepcidin pathway within 4 weeks may contribute to iron imbalance in premature infants.

Iron status in early childhood is modified by diet, sex and growth: Secondary analysis of a randomized controlled vitamin D trial

BACKGROUND & AIMS

During early childhood the risk of iron deficiency (ID) is high. Serum ferritin serves as a marker of iron status. We explored prevalence of ID and iron deficiency anemia (IDA), and identified determinants of iron status in infants and toddlers.

METHODS

We performed a secondary analysis of the Vitamin D intervention in infants (VIDI) study in Finnish healthy term infants. According to study protocol, at 12- and 24-months of age iron status, growth and dietary intakes were evaluated. ID was defined as serum ferritin <10 μg/L and IDA as serum ferritin <10 μg/L and Hb <112 g/L. For the present study, altogether 766 children provided data (N = 498 infants at 12 months, N = 508 toddlers at 24 months).

RESULTS

ID prevalence increased from 14% in infants to 20% in toddlers. IDA prevalence was 3% at both time points. In infants, ID and IDA were more common in boys than in girls (19% vs. 9%, p = 0.001 and 5% vs. 1%, p = 0.039) but no sex-difference in toddlers was observed. Of infants, 30% had daily iron intake below average requirement of 5 mg/day. Higher daily iron intake per body weight (mg/kg) independently associated with higher infant serum ferritin (B (95% CI) 0.30 (0.04, 0.56), p = 0.026). Correlation between iron intake and ferritin was stronger in infants with ID than in infants without ID. Breastfeeding was more common (63% vs. 35%, p < 0.001) among ID infants than in infants without ID. In toddlers, frequent consumption of milk products independently associated with lower ferritin (B (95% CI) -0.03 (-0.05, -0.01), p = 0.001). Consumption of meat and fish associated with better iron status. Serum ferritin at both time points associated with duration of gestation and growth. The association of growth and ferritin was age-dependent in boys, while in girls, faster growth associated consistently with lower ferritin.

CONCLUSIONS

In Northern European healthy infants and toddlers ID is common. The intake of iron remains below recommendations and food consumption and iron intake associate with iron status. Further studies are warranted to assess significance of ID on child development and clinical health outcomes. The project protocol is registered at ClinicalTrials.gov: NCT01723852.

Association of vitamin A with anemia and serum hepcidin levels in children aged 6 to 59 mo

OBJECTIVE

This study evaluates the association of serum retinol, hepcidin levels, and anemia in children.

METHODS

This cross-sectional study included 312 children, ages 6 to 59 mo, from Rio de Janeiro, Brazil. The association between hepcidin and retinol levels, hematologic parameters, and body mass index (BMI) was analyzed using a generalized linear model with and without adjustment for C-reactive protein (CRP) level. Logistic regression analysis was used to test anemia as an outcome and serum retinol level as a predictive variable using the odds ratio (OR) function.

RESULTS

Anemia was present in 14.6% of the children, 5.8% presented iron deficiency anemia, and 9.6% had vitamin A deficiency. The increase in serum retinol levels reduced the chances of anemia (OR = 0.13; confidence interval = 0.29-0.59). When CRP level was not adjusted for in the multiple regression analyses, retinol, ferritin levels, and BMI/age were predictors of serum hepcidin levels (β = -3.36, 0.14, 1.02, respectively; P = 0.032). Accordingly, serum retinol levels were inversely associated with CRP levels (β = -0.025 and P < 0.001).

CONCLUSIONS

The association between serum retinol and hepcidin levels in children ages 6 to 59 mo seems to be dependent on inflammation. Taken together, the results reinforce the need for the development of further studies to better understand the relationship between vitamin A and anemia of inflammation.

Isotopic measurement of iron requirements in sub-Saharan African children

BACKGROUND

Prevention of iron deficiency in African children is a public health priority. Current WHO/FAO estimations of iron requirements are derived from factorial estimates based on healthy, iron-sufficient "model" children using data derived mainly from adults.

OBJECTIVES

In this study, we aimed to quantify iron absorption, loss, and balance in apparently healthy 5- to 7-y-old children living in rural Africa.

METHODS

We directly measured long-term iron absorption and iron loss in a 2-y observational study in Malawian children (n = 48) using a novel stable iron isotope method.

RESULTS

Of the 36 children with height-for-age and weight-for-age z scores ≥-2, 13 (36%) were iron deficient (soluble transferrin receptor >8.3 mg/L) and 23 were iron sufficient. Iron-deficient children weighed more than iron-sufficient children [mean difference (95% CI): +2.1 (1.4, 2.7) kg; P = 0.01]. Mean iron losses did not differ significantly between iron-deficient and iron-sufficient children and were comparable to WHO/FAO median estimates of 19 µg/(d × kg). In iron-sufficient children, median (95% CI) dietary iron absorption was 32 (28, 34) µg/(d × kg), comparable to WHO/FAO-estimated median requirements of 32 µg/(d × kg). In iron-deficient children, absorption of 28 (25, 30) µg/(d × kg) was not increased to correct their iron deficit, likely because of a lack of bioavailable dietary iron. Twelve children (25%) were undernourished (underweight, stunted, or both).

CONCLUSIONS

Our results suggest that WHO/FAO iron requirements are adequate for healthy iron-sufficient children in this rural area of Malawi, but iron-deficient children require additional bioavailable iron to correct their iron deficit.

The critical roles of iron during the journey from fetus to adolescent: Developmental aspects of iron homeostasis

Iron is indispensable for human life. However, it is also potentially toxic, since it catalyzes the formation of harmful oxidative radicals in unbound form and may facilitate pathogen growth. Therefore, iron homeostasis needs to be tightly regulated. Rapid growth and development require large amounts of iron, while (especially young) children are vulnerable to infections with iron-dependent pathogens due to an immature immune system. Moreover, unbalanced iron status early in life may have effects on the nervous system, immune system and gut microbiota that persist into adulthood. In this narrative review, we assess the critical roles of iron for growth and development and elaborate how the body adapts to physiologically high iron demands during the journey from fetus to adolescent. As a first step towards the development of clinical guidelines for the management of iron disorders in children, we summarize the unmet needs regarding the developmental aspects of iron homeostasis.

Hepcidin-Mediated Hypoferremia Disrupts Immune Responses to Vaccination and Infection

BACKGROUND

How specific nutrients influence adaptive immunity is of broad interest. Iron deficiency is the most common micronutrient deficiency worldwide and imparts a significant burden of global disease; however, its effects on immunity remain unclear.

METHODS

We used a hepcidin mimetic and several genetic models to examine the effect of low iron availability on T cells in vitro and on immune responses to vaccines and viral infection in mice. We examined humoral immunity in human patients with raised hepcidin and low serum iron caused by mutant TMPRSS6. We tested the effect of iron supplementation on vaccination-induced humoral immunity in piglets, a natural model of iron deficiency.

FINDINGS

We show that low serum iron (hypoferremia), caused by increased hepcidin, severely impairs effector and memory responses to immunizations. The intensified metabolism of activated lymphocytes requires the support of enhanced iron acquisition, which is facilitated by IRP1/2 and TFRC. Accordingly, providing extra iron improved the response to vaccination in hypoferremic mice and piglets, while conversely, hypoferremic humans with chronically increased hepcidin have reduced concentrations of antibodies specific for certain pathogens. Imposing hypoferremia blunted the T cell, B cell, and neutralizing antibody responses to influenza virus infection in mice, allowing the virus to persist and exacerbating lung inflammation and morbidity.

CONCLUSIONS

Hypoferremia, a well-conserved physiological innate response to infection, can counteract the development of adaptive immunity. This nutrient trade-off is relevant for understanding and improving immune responses to infections and vaccines in the globally common contexts of iron deficiency and inflammatory disorders.

FUNDING

Medical Research Council, UK.

Artemisinin Activity in Red Blood Cells from Anemic Children

Artemisinin combination therapies are the current frontline therapy for falciparum malaria. Artemisinin is activated by heme iron, and the consequent production of reactive oxygen species and carbon-centered radicals results in rapid parasite clearance. Red blood cells (RBCs) from anemic iron-deficient individuals have decreased levels of heme, and such deficiencies are highly prevalent among children and pregnant women in malaria-endemic countries. We, therefore, investigated the possibility that host anemia could impair artemisinin activity and alter the drug sensitivity of artemisinin-resistant strains of Plasmodium falciparum. We collected RBCs from anemic (n = 35) and nonanemic (n = 11) Gambian children between the ages of 2 and 24 months. Parasites grown in RBCs from both groups were assessed in vitro using the ring-stage survival assay with artemisinin-resistant and artemisinin-sensitive strains of P. falciparum. No differences were found in artemisinin sensitivity (P > 0.05), and there was no correlation between artemisinin activity and host hemoglobin levels. Standard antimalarial drug activity assays for representatives of the major classes of antimalarial drugs found no differences in the IC₅₀ values against P. falciparum between anemic and nonanemic RBCs. We conclude that host anemia does not influence artemisinin activity.

Iron deficiency

Iron deficiency is one of the leading contributors to the global burden of disease, and particularly affects children, premenopausal women, and people in low-income and middle-income countries. Anaemia is one of many consequences of iron deficiency, and clinical and functional impairments can occur in the absence of anaemia. Iron deprivation from erythroblasts and other tissues occurs when total body stores of iron are low or when inflammation causes withholding of iron from the plasma, particularly through the action of hepcidin, the main regulator of systemic iron homoeostasis. Oral iron therapy is the first line of treatment in most cases. Hepcidin upregulation by oral iron supplementation limits the absorption efficiency of high-dose oral iron supplementation, and of oral iron during inflammation. Modern parenteral iron formulations have substantially altered iron treatment and enable rapid, safe total-dose iron replacement. An underlying cause should be sought in all patients presenting with iron deficiency: screening for coeliac disease should be considered routinely, and endoscopic investigation to exclude bleeding gastrointestinal lesions is warranted in men and postmenopausal women presenting with iron deficiency anaemia. Iron supplementation programmes in low-income countries comprise part of the solution to meeting WHO Global Nutrition Targets.

The effect of iron dosing schedules on plasma hepcidin and iron absorption in Kenyan infants

BACKGROUND

In adults, oral iron doses increase plasma hepcidin (PHep) for 24 h, but not for 48 h, and there is a circadian increase in PHep over the day. Because high PHep decreases fractional iron absorption (FIA), alternate day iron dosing in the morning may be preferable to consecutive day dosing. Whether these effects occur in infants is uncertain.

OBJECTIVE

Using stable iron isotopes in Kenyan infants, we compared FIA from morning and afternoon doses and from consecutive, alternate (every second day) and every third day iron doses.

METHODS

In prospective studies, we measured and compared FIA and the PHep response from 1) meals fortified with a 12-mg iron micronutrient powder given in the morning or afternoon (n = 22); 2) the same given on consecutive or alternate days (n = 21); and 3) a 12-mg iron supplement given on alternate days or every third day (n = 24).

RESULTS

In total, 65.7% of infants were anemic. In study 1, PHep did not differ between morning and afternoon (P = 0.072), and geometric mean FIA[-SD, +SD](%) did not differ between the morning and afternoon doses [15.9 (8.9, 28.6) and 16.1 (8.7, 29.8), P = 0.877]. In study 2, PHep was increased 24 h after oral iron (P = 0.014), and mean FIA [±SD](%) from the baseline dose [23.3 (10.9)] was greater than that from the consecutive day dose (at 24 h) [20.1 (10.4); P = 0.042] but did not differ from the alternate day dose (at 48 h) [20.9 (13.4); P = 0.145]. In study 3, PHep was not increased 48 and 72 h after oral iron (P = 0.384), and the geometric mean FIA[-SD, +SD](%) from doses given at baseline, alternate days, and every third day did not differ [12.7 (7.3, 21.9), 13.8 (7.8, 24.2), and 14.8 (8.8, 24.8), respectively; P = 0.080].

CONCLUSIONS

In Kenyan infants given 12 mg oral iron, morning and afternoon doses are comparably absorbed, dosing on consecutive days increases PHep and modestly decreases iron absorption compared with alternate day dosing, and dosing on alternate days or every third day does not increase PHep or decrease absorption. This trial was registered at clinicaltrials.gov as NCT02989311 and NCT03617575.

Hepcidin, Serum Iron, and Transferrin Saturation in Full-Term and Premature Infants during the First Month of Life: A State-of-the-Art Review of Existing Evidence in Humans

Neonates regulate iron at birth and in early postnatal life. We reviewed literature from PubMed and Ovid Medline containing data on umbilical cord and venous blood concentrations of hepcidin and iron, and transferrin saturation (TSAT), in human neonates from 0 to 1 mo of age. Data from 59 studies were used to create reference ranges for hepcidin, iron, and TSAT for full-term-birth (FTB) neonates over the first month of life. In FTB neonates, venous hepcidin increases 100% over the first month of life (to reach 61.1 ng/mL; 95% CI: 20.1, 102.0 ng/mL) compared with umbilical cord blood (29.7 ng/mL; 95% CI: 21.1, 38.3 ng/mL). Cord blood has a high concentration of serum iron (28.4 μmol/L; 95% CI: 26.0, 31.1 μmol/L) and levels of TSAT (51.7%; 95% CI: 46.5%, 56.9%). After a short-lived immediate postnatal hypoferremia, iron and TSAT rebounded to approximately half the levels in the cord by the end of the first month. There were insufficient data to formulate reference ranges for preterm neonates.

Standardized serum hepcidin values in Dutch children: Set point relative to body iron changes during childhood

BACKGROUND

Use of serum hepcidin measurements in pediatrics would benefit from standardized age- and sex-specific reference ranges in children, in order to enable the establishment of clinical decision limits that are universally applicable.

PROCEDURE

We measured serum hepcidin-25 levels in 266 healthy Dutch children aged 0.3-17 years, using an isotope dilution mass spectrometry assay, standardized with our commutable secondary reference material (RM), assigned by a candidate primary RM.

RESULTS

We constructed age- and sex-specific values for serum hepcidin and its ratio with ferritin and transferrin saturation (TSAT). Serum hepcidin levels and hepcidin/ferritin and TSAT/hepcidin ratios were similar for both sexes. Serum hepcidin and hepcidin/ferritin ratio substantially declined after the age of 12 years and TSAT/hepcidin ratio gradually increased with increasing age. Serum hepcidin values for Dutch children <12 years (n = 170) and >12 years (n = 96) were 1.9 nmol/L (median); 0.1-13.1 nmol/L (p2.5-p97.5) and 0.9 nmol/L; 0.0-9.1 nmol/L, respectively. Serum ferritin was the most significant correlate of serum hepcidin in our study population, explaining 15.1% and 7.9% of variance in males and females, respectively. Multivariable linear regression analysis including age, blood sampling time, iron parameters, ALT, CRP, and body mass index as independent variables showed a statistically significant negative association between age as a dichotomous variable (≤12 vs >12 years) and log-transformed serum hepcidin levels in both sexes.

CONCLUSIONS

We demonstrate that serum hepcidin relative to indicators of body iron is age dependent in children, suggesting that the set point of serum hepcidin relative to stored and circulating iron changes during childhood.

The Importance of Iron Status for Young Children in Low- and Middle-Income Countries: A Narrative Review

Early childhood is characterised by high physiological iron demand to support processes including blood volume expansion, brain development and tissue growth. Iron is also required for other essential functions including the generation of effective immune responses. Adequate iron status is therefore a prerequisite for optimal child development, yet nutritional iron deficiency and inflammation-related iron restriction are widespread amongst young children in low- and middle-income countries (LMICs), meaning iron demands are frequently not met. Consequently, therapeutic iron interventions are commonly recommended. However, iron also influences infection pathogenesis: iron deficiency reduces the risk of malaria, while therapeutic iron may increase susceptibility to malaria, respiratory and gastrointestinal infections, besides reshaping the intestinal microbiome. This means caution should be employed in administering iron interventions to young children in LMIC settings with high infection burdens. In this narrative review, we first examine demand and supply of iron during early childhood, in relation to the molecular understanding of systemic iron control. We then evaluate the importance of iron for distinct aspects of physiology and development, particularly focusing on young LMIC children. We finally discuss the implications and potential for interventions aimed at improving iron status whilst minimising infection-related risks in such settings. Optimal iron intervention strategies will likely need to be individually or setting-specifically adapted according to iron deficiency, inflammation status and infection risk, while maximising iron bioavailability and considering the trade-offs between benefits and risks for different aspects of physiology. The effectiveness of alternative approaches not centred around nutritional iron interventions for children should also be thoroughly evaluated: these include direct targeting of common causes of infection/inflammation, and maternal iron administration during pregnancy.