Iron Supplements with Distinct Absorption Efficiencies May Differentially Affect Infant Gut Microbiome

Abstract

Iron supplementation is widely used to treat iron deficiency anemia (IDA) in human infants, but its effects on the developing gut microbiome remain inconsistent across studies. Differences in supplement formulation may influence iron absorption efficiency and the amount of unabsorbed iron reaching the colon, thereby differentially shaping microbial composition and function. This study analyzed 16S rRNA sequencing data from 6-month-old healthy (n=37) and anemic (n=40) infants to determine whether two iron supplements, ferrous sulfate (FeSO₄) and micronutrient powder (MNP), differentially affect gut microbial diversity, taxonomic composition, and functional potential. In particular, MNP was hypothesized to have greater iron absorption potential compared to FeSO₄ as it contains additional iron absorption enhancers. These outcomes were assessed in diversity analyses, core microbiome and indicator species analysis, differential abundance (DESeq2), and predicted functional profiling (PICRUSt2). No significant differences in overall microbial diversity were observed across supplementation groups. However, targeted taxonomic and functional shifts were identified in anemic infants. FeSO₄ was associated with an increased number of unique taxa, the enrichment of opportunistic genera, and depletion of commensals. Moreover, both FeSO₄ and MNP altered the relative abundance of commensal and opportunistic genera. At the functional level, both supplements were associated with the under-representation of metabolic pathways compared to no supplementation. MNP additionally promoted pathways relating to amino acids, cofactors, and vitamin metabolism. Together, these findings suggest that iron supplement formulations with distinct absorption efficiencies can differentially influence the infant gut microbiome through taxonomic and functional changes without broad community-level structural shifts.