Breastfeeding and externalising problems: A quasi-experimental design with a national cohort

Lisa-Christine Girard, Orla Doyle, Richard E. Tremblay

Research output: Contribution to journalArticlepeer-review


Objective: Evidence from correlational studies supporting the benefits of breastfeeding on children’s externalising problems is mixed. Quasi-experimental approaches can help in better understanding possible ‘effects’. We aimed to investigate the longitudinal impact of breastfeeding on externalising problems from childhood into adolescence.

Study Design: Participants included ~ 5,000 full-term children, from the Growing Up in Ireland child cohort. Externalising problems (conduct problems and hyperactivity) were assessed using both the parent and teacher versions of the Strengths and Difficulties Questionnaire when children were age nine and 13. Maternal reports were used to collect retrospective information on breastfeeding. Propensity score matching, adjusting for multiple testing, was used to compare the average treatment effects for children who were breastfed.

Results: Post matching results revealed statistically significant reductions in hyperactivity at age nine, using both maternal and teacher reports (difference score -0.48, 95% CI -0.85, -0.11; and -0.51, 95% CI -0.90, -0.12, respectively), for children who were breastfed between 6 and 12 months, but not thereafter. These effects were not maintained at age 13. Moreover, no effects of breastfeeding on conduct problems were found at any age, regardless of duration, using either maternal or teacher report.

Conclusions: While some benefits of breastfeeding were found, compatible with a temporary modest reduction in hyperactivity, related to being breastfed for 26-50 weeks, these results must be viewed in the context of reliance of propensity score matching on observable characteristics. Additionally, our results are suggestive of a potential non-linear dose-response of breastfeeding on hyperactivity.
Original languageEnglish
Pages (from-to)877-884
JournalEuropean Child and Adolescent Psychiatry
Issue number7
Early online date24 Nov 2017
Publication statusPublished - Jul 2018


  • conduct problems
  • hyperactivity
  • breastfeeding
  • longitudinal cohort study
  • quasi-experimental approach


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