Malaria is a cause of iron deficiency in African children

Abstract

Malaria and iron deficiency (ID) are common and interrelated public health problems in African children. Observational data suggest that interrupting malaria transmission reduces the prevalence of ID¹. To test the hypothesis that malaria might cause ID, we used sickle cell trait (HbAS, rs334 ), a genetic variant that confers specific protection against malaria², as an instrumental variable in Mendelian randomization analyses. HbAS was associated with a 30% reduction in ID among children living in malaria-endemic countries in Africa (n = 7,453), but not among individuals living in malaria-free areas (n = 3,818). Genetically predicted malaria risk was associated with an odds ratio of 2.65 for ID per unit increase in the log incidence rate of malaria. This suggests that an intervention that halves the risk of malaria episodes would reduce the prevalence of ID in African children by 49%.

Extended Data Fig.1. A meta-analysis of previous African studies investigating the effect of α-thalassemia and G6PD A and A-polymorphisms on uncomplicated febrile malaria.

Overall represents a fixed-effect meta-analysis of study-specific incidence rate ratio (IRR) by genetic polymorphism. Error bars indicate 95% confidence intervals. n shows the number of individuals included in the analysis. Few studies included G6PD homozygous females and numbers were small (Table S2). Het, heterozygous; Hom, homozygous.

Extended Data Fig.2. A meta-analysis of the effect of sickle cell trait on iron deficiency anemia (IDA).

Overall represents a fixed-effect meta-analysis of cohort-specific odds ratios. Error bars indicate 95 % confidence intervals. n shows the number of individuals included in the analysis. Numbers for IDA are fewer compared to those for ID since not all children had hemoglobin concentrations measured.

Extended Data Fig.3. A meta-analysis of the effect of sickle cell trait on iron deficiency (ID) regression-corrected for inflammation.

ID was defined using ferritin levels adjusted for the effects of inflammation using a regression-correction approach as developed by BRINDA. Overall represents a fixed-effect meta-analysis of cohort-specific odds ratios. Error bars indicate 95 % confidence intervals. n shows the number of individuals included in the analysis.

Extended Data Fig.4. A meta-analysis of the effect of sickle cell trait on uncomplicated febrile malaria.

Overall represents a fixed-effect meta-analysis of study-specific incidence rate ratio (IRR). Error bars indicate 95 % confidence intervals. n shows the number of individuals included in the analysis.

Extended Data Fig.5. How HbAS,a genetic proxy for malaria exposure,may protect children from iron deficiency.

a, Individuals carrying normal beta hemoglobin gene (HbAA) are not protected from malaria. Malaria up-regulates production of hepcidin through inflammatory and non-inflammatory pathways and by increasing the prevalence of other infections. Hepcidin in turn blocks iron absorption.b,Sickle cell trait (HbAS) partially protects individuals from malaria infection, therefore inflammation is reduced leading to reduced hepcidin stimulation and increased iron absorption.

Extended Data Fig.6. Relationship between geometric mean hepcidin concentrations, malaria parasitemia and inflammation.

Error bars indicate 95 % confidence intervals. n indicates biologically independent samples. Horizontal dotted line indicates the threshold of hepcidin above which iron absorption is inhibited (5.5 μg/L). Inflammation was defined as CRP >5 mg/L, ACT >O.6g/L or AGP >1 g/L. Malaria was defined as a blood slide positive for asexual P. falciparum parasites. Hepcidin was measured in the Burkina Faso, Western Kenya, Uganda, The Gambia, and Kilifi, Kenya cohorts.

Fig.1. Sickle cell trait (HbAS) is associated with protection from ID.

a, Map of malaria in Africa showing the predicted posterior predictions of age-standardized P. falciparum prevalence (PfPR_2-10) taken from Snow et al. and the location of the current study sites with data on sickle cell trait (HbAS). The map was reproduced with permission.b, Prevalence (%) of malaria parasitemia, HbAS and ID for each study site.c, Summary results of the effect of HbAS on ID by study site. ‘Overall’ represents a fixed-effect meta-analysis of study-specific odds ratios (ORs).d, ORs for the associations between sickle cell trait and the variables age, sex, inflammation and underweight. For age, sex and inflammation, n =7,453 biologically independent samples were used, and for underweight, n = 6,428 biologically independent samples were used. Inflammation was defined as CRP >5 mgl^-1 or ACT > O.6gl^-1 or AGP >lgl^-1. Underweight was defined as a WHO 2006 reference weight-for-age z score <-2. All error bars indicate 95% CIs. HbAA, normal hemoglobin.

Fig.2. How malaria might cause a hepcidin-mediated blockade of iron absorption and recycling leading to ID.

The prevalences (%) of ID (a) and IDA (b) were lower in African children carrying sickle cell trait (HbAS), a genetic variant that protects against malaria, than in those with normal hemoglobin (HbAA) in malaria-endemic sites but not in sites without malaria. P values were derived from logistic regression analyses adjusted for age,sex, inflammation and study site. c, Geometric means of hepcidin concentrations were higher in children with malaria parasitemia or severe malaria compared to those without. P values were derived from two-tailed Student’s t-tests. d, Prevalence (%) of inflammation was lower in individuals with HbAS than in those with HbAA in malaria-endemic sites but not in sites without malaria.P values were derived from logistic regression analyses adjusted for age, sex and study site. e, Geometric means of hepcidin concentrations increase with increasing CRP concentrations and remain above threshold for iron absorption at almost all deciles of CRP in children with malaria parasitemia. The brown line shows children with malaria parasitemia, and the blue line shows those without parasitemia. The yellow line shows the point at which inflammation is clinically diagnosed. The red horizontal line indicates the threshold of hepcidin above which iron absorption is inhibited (5.5μgl^-1). Data were pooled for malaria-endemic sites and for sites without malaria (Jackson Heart Study (JHS) and Nairobi). Hepcidin levels were measured in the Burkina Faso, Western Kenya, Uganda, The Gambia and Kilifi, Kenya cohorts. CRP levels were measured in all sites except The Gambia.n indicates biologically independent samples. All error bars indicate 95% CIs. Cp, ceruloplasmin; DMT1, divalent metal transporter 1; FPN, ferroportin; GIT, gastrointestinal tract; Par, malaria parasitemia; Pf,P. falciparum; RBC, red blood cell; Tf, transferrin; TfR, transferrin receptor.