UC Davis

Iron deficiency (ID) during infancy is harmful to health and development. Iron supplements such as iron drops and fortified infant formula prevent ID effectively but typically provide 10-20x more iron than breast milk and may have adverse health and development effects when provided to infants not at high risk for ID. Adverse effects on growth, gut microbiota development, trace mineral status, neurodevelopment, and risk of morbidity have been observed, but these effects have been poorly understood. These effects and the underlying mechanisms were investigated underlying utilizing a pre-weanling rat supplementation model. In the first study, Sprague Dawley rat litters were randomly assigned to receive daily vehicle control (CON) supplementation, or 10 mg iron/kg body weight (BW) (representative of the typical daily iron intake from fortified formula) as either ferrous sulfate (FS) or ferrous bis-glycinate chelate (FC), a novel bioavailable form of iron. FS and FC groups had comparable liver iron, hemoglobin, and hematocit values that were higher than CON (p < 0.0001) at postnatal day (PD) 15 after 2 weeks of supplementation. BW gain was unaffected by group, but FS brains were heavier than FC brains (p < 0.05). In the second study, short- and long-term effects of routine iron levels on gut microbiota development were assessed. Iron supplementation induced over 10,000-fold loss of Lactobacillus commensal bacteria in the gut compared to CON. Gut microbiome composition and diversity depended on iron form: FS and FC gut microbiome communities were distant, and while iron reduced gut microbiota diversity, FC microbiomes were even less diverse than FS as compared to CON. Long-term effects of iron were revealed when an additional cohort of groups were supplemented with FS, FC, or CON up to weaning: adult gut microbiome compositions 6 weeks after weaning depicted a 10,000-fold loss of Lactobacillus if they had received iron prior to weaning, and overall microbiome also which form was provided (FS or FC). The results of the first two studies concluded that iron provision prior to weaning elevates iron status beyond needs and adversely effects long-term microbiome composition. Additionally, it was concluded that microbiome and development effects depend on the form of iron provided. A final FS dose response study sought to identify the role of the excess iron dose in adverse health and development outcomes and found that increasing daily iron supplementation to 90 mg iron/kg BW further elevated liver iron loading, reduced pre-weanling rat weight gain and brain size, elevated inflammation, and altered levels of copper and zinc in the liver. The results of the final experiment suggest that mineral interactions and inflammatory signaling are implicated in adverse growth and development effects of excess iron. In summary, results from all three studies support that excess iron disrupts growth and development, and these effects depend upon iron form and dose. The findings provide novel evidence it is likely that the gut microbiota, inflammatory signaling, and mineral interactions may play important roles in the adverse outcomes of iron provision during infancy.