Breastfeeding limits the adverse impact of socioeconomic status on child health by modifying 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 CHILD cohort, we analyzed modifiable pathways linking SES to child health and found that the infant gut microbiota plays a key mediating role. Breastfeeding was 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, was linked to protection against adverse outcomes from SES. We observed similar associations in the independent COPSAC ₂₀₁₀ cohort, including links among SES, breastfeeding, child health, the microbiota, and B. infantis . Together, these results suggest the 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.