Mental health problems run in families. This arises from a range of genetic and environmental factors.

Recently, we have seen the impact that the human microbiome has on physical health (e.g inflammatory bowel disease, asthma, obesity) and mental health (depression, anxiety, autism).

Like mental health, the microbiome also runs in families, likely because of environmental transfer of microbiota between family members and, in particular, the seeding of the neonatal microbiome during the birth process. We wondered whether the sharing of microbiomes within families may partially explain familial similarities in mental health.

It is not possible to conduct an experiment, interrupting the transfer of microbiota from mother to child, to see if this had an impact on transfer of intergenerational risk for mental health problems. However, nature (helped along by NHS maternity services) provides us with a natural experiment: Approximately 20-25% of births are via caesarean section, and there is mounting evidence that this results in substantially lower mother-child microbiome transfer than vaginal birth. This microbiome transfer process can be further interrupted by other factors, including prenatal/perinatal antibiotic use and breastfeeding practices.

This study will explore the impact of early-life microbiome transfer on the intergenerational transmission of mental health problems.