Sibling Exposure Boosts Infant Gut Microbiome Recovery

New research indicates that having older siblings may help infants born via Cesarean section recover their gut microbiome more closely to that of vaginally delivered babies by age one, potentially reducing associated health risks.

The findings come from a study published in Nature Communications, which analyzed data from the COPSAC2010 birth cohort in Denmark and validated the results in the independent Canadian CHILD cohort. Researchers developed a restoration score to measure how closely the gut microbiome of one-year-olds resembled that of infants delivered vaginally.

In the COPSAC2010 cohort, which included 700 children, the study found that early-life gut bacteria and having older siblings were significant predictors of microbiome restoration by age one. This restoration was linked to increased abundances of specific bacteria associated with microbiome recovery.

The beneficial effect of sibling exposure appeared to be mediated through these restoration-associated bacteria, suggesting a direct microbial mechanism by which older siblings influence gut microbiome development in younger children.

Importantly, the restoration score — which incorporated delivery mode, sibling exposure, and early bacterial patterns — was also associated with later asthma outcomes. Higher restoration scores correlated with lower asthma risk, suggesting that microbiome recovery may play a protective role against respiratory conditions.

The researchers replicated these findings in the CHILD cohort, confirming that the relationship between early-life bacteria, sibling exposure, and microbiome restoration holds across different populations and strengthens the validity of the observations.

While the study identifies strong associations, it does not establish causation. The researchers note that environmental and ecological interactions within the household likely contribute to microbial exchange, but further study is needed to fully understand the mechanisms involved.

These insights highlight the potential of early-life exposures — particularly sibling contact — to modulate the long-term effects of Cesarean delivery on gut microbiome development and related health outcomes.