Breastfeeding duration and vagal regulation of infants and mothers

•Vagal regulation, indexed by RSA, supports self-regulation and social engagement•The longer breastfeeding duration is associated with lower infant RSA throughout the still-face paradigm•The longer breastfeeding duration is associated with higher overall RSA levels in mothers throughout the still-face paradigm•Continuation in breastfeeding contributes to infant adaptive vagal regulation during an interaction