Intranasal oxytocin increases breast milk oxytocin, but has a reduced effect in depressed mothers: A randomized controlled trial.

UNLABELLED: Oxytocin (OT) plays pivotal roles in stress regulation, mother-infant bonding, and breastfeeding, all of which are adversely impacted by postnatal depression (PND). In a double-blind, randomized controlled trial, we assessed endogenous OT concentrations first in the breast milk of new mothers at baseline, and second following the administration of exogenous OT compared to a placebo delivered via a nasal spray. METHOD: Participants were mothers (N = 62, aged 23-42 years) and their infants (aged 3-9 months). Each mother underwent screening for PND symptoms using the Edinburgh Postnatal Depression Scale (EPDS). N = 26 mothers scored above the cut-off point (≥9) on the EPDS, and N = 36 mothers scored below. Breast milk samples, collected during breastfeeding, were assayed for OT content. RESULTS: Baseline endogenous OT concentration in breast milk was not associated with maternal low mood. Exogenous OT administration was associated with a significant increase in breast milk OT, but with reduced effect in mothers experiencing symptoms of PND compared to control mothers. CONCLUSIONS: Future studies should test if breast milk OT exhibits a protective role against the developmental disadvantages of maternal PND on children. The current findings may reflect a possible disruption of the interaction between the central and peripheral OT pathways during breastfeeding in mothers experiencing symptoms of PND. These insights shed new light on the potential biological mechanisms involved in the transference of mental health vulnerabilities from mothers to infants.