Association of infants' feeding pattern up to 2 years postpartum with mothers' mental and physical health: the Japan Environment and Children's Study

Background: Exclusive breastfeeding, a longer breastfeeding duration, and interaction with the baby during lactation improve mothers' mental health. However, few studies have targeted women around 2.5 years after childbirth, when women are still considered to have been in a period of mental and physical health vulnerability. This study examined this aspect in a large cohort of mother-child pairs. Methods: Data were obtained from 85,735 mothers in an ongoing nationwide birth cohort study in Japan. Exposures were exclusive breastfeeding (yes/no), continued breastfeeding up to 2 years (yes/no), and interaction with the baby during feeding (yes/no). Outcomes were mothers' mental and physical health 2.5 years after childbirth measured using Mental and Physical Component Summary scores (MCS and PCS scores, respectively) from the 8-item Short-Form Health Survey. Generalized additive mixed model analysis was used to derive each estimate for the three exposures and their interactions, with each “no” answer as reference. Results: Exclusive breastfeeding and interaction with the baby during feeding were associated with MCS score increases of 0.28 (95%CI: 0.10–0.47) and 0.41 (95%CI: 0.29–0.54), respectively. However, no associations were found for continued breastfeeding up to 2 years and no interactions were identified. No significant differences were observed for PCS scores. Limitations: All variables were measured using a self-administered questionnaire. Conclusions: Continued exclusive breastfeeding until 6 months and interaction with the baby during feeding may help to promote mother's mental health 2.5 years after childbirth. These findings further strengthen the rationale for the World Health Organization's recommended lactation practices.