Maternal cortisol and emotional complaints alter breast milk’s microbiome composition

Breast milk (BM) is considered the “gold standard” of nutrition due to its many benefits for the infant. On the other hand, the challenges of pregnancy can lead to increased stress in some women, which may affect BM quality. Although studies have demonstrated a negative link between maternal psychopathology and child development, it remains unclear how maternal psychobiological changes can be intergenerationally transmitted. Aims We investigated the associations between maternal biological stress, depressive symptoms, self-reported stress and anxiety symptoms and the BM microbiome. Further, we analysed these parameters in relation to BM glucocorticoid concentrations and explored the influence of BM glucocorticoids on BM bacterial composition. Methods N=100 women completed standardised questionnaires (e.g. EPDS, STAI, GAS) at 34-36 weeks gestation and in the early postpartum; and sampled saliva at 34-36 and 38 weeks gestation. BM samples were collected in the early postpartum. Microbiota was analysed using 16S rRNA amplicon sequencing. Results Prenatal GAS and pregnancy-related symptoms (sum) were negatively correlated with Alphaproteobacteria (τ = - 0.2137, FDR = 0.0199*; τ = - 0.1805 FDR = 0.0798*), whereas in the postpartum period, the STAI-S scores were negatively correlated with different taxa. Postpartum-related symptoms (sum) were also linked to decreased Propionibacteriales . Salivary cortisol AUCg at 34-36 weeks was negatively correlated with Actinomycetia (τ = -0.1633, FDR = 0.0630*) and Clostridia (τ = -0.1824, FDR = 0.0630*). BM cortisol was negatively correlated with Staphylococcus (τ = - 0.2047, FDR = 0.0885*) and positively correlated with BM alpha diversity. No associations emerged between psychobiological parameters and BM glucocorticoids. Conclusions Increased perinatal emotional complaints and prenatal cortisol AUCg were associated with decreased commensal bacteria, whereas enhanced BM cortisol was linked to increased alpha diversity and reduced Staphylococcus . These findings suggest a negative relation between high maternal psychobiological complaints and commensal milk microbiota.