Iron and the Human Gut Microbiota

Fractional iron absorption from iron-fortified foods or oral iron supplements is generally low; often less than 10% of the iron dose is absorbed. Thus, the majority of iron passes unabsorbed into the colon where it might favor growth of potential enteropathogens, for which iron is crucial for replication and virulence, over important commensal “barrier” strains such as bifidobacteria and lactobacilli, which require little or no iron. Studies conducted in African infants and children have shown that in settings with poor hygiene and a high burden of infection and inflammation, iron fortification and supplementation adversely affect the gut microbiota: by decreasing beneficial bifidobacteria and lactobacilli, by increasing enteropathogens (e.g., pathogenic Escherichia coli), and by increasing gut inflammation. These adverse changes in the gut microbiota provide a plausible mechanism for the reported increased risk of diarrhea with provision of iron to infants and children in low-resource settings. Providing a low dose of iron that is highly bioavailable and co-provision of prebiotic galacto-oligosaccharides have recently been shown to be promising strategies to mitigate adverse effects of iron on the infant gut microbiota.