Breastfeeding may lessen socioeconomic disparities in child health through differences in the infant gut microbiome.

Lower familial socioeconomic status (SES) is linked to increased childhood disease risk. Since SES has no inherent biological basis, identifying how it becomes physiologically embedded is essential for equitable intervention. Using data from the Canadian CHILD birth cohort (n = 2,752) with replication in the Danish Copenhagen Prospective Studies on Asthma in Childhood 2010 (COPSAC2010) cohort (n = 681), we analyze modifiable pathways linking SES to child health and find that the infant gut microbiota plays a key mediating role. Breastfeeding is associated with a stabilized infant microbiota, buffering against environmental impacts and reducing health risks in lower SES contexts. The presence of Bifidobacterium infantis, enriched through breastfeeding, is linked to protection against adverse outcomes from SES. Together, these results suggest that improving breastfeeding rates and restoring breastfeeding-enriched microbes, like B. infantis, may help buffer early biological impacts of social inequality and support healthier trajectories for children growing up in industrialized settings.