Duration of Breastfeeding Mediates the Association Between Early Socioeconomic Risk and Child Vocabulary at Age 4

Objective: Early-life socioeconomic disadvantage is associated with both obesity and lower cognitive abilities in childhood. One theorized underlying mechanism is breastfeeding duration because breast milk contains nutrients that can promote healthy adiposity profiles and stimulate brain development. However, studies have rarely examined these potential associations with child body mass index (BMI) in high-income Western countries, much less investigated breastfeeding duration as a mediator of the relationship between childhood socioeconomic status (SES) and later child vocabulary. The current study aimed to prospectively examine associations between early-life family socioeconomic risk and both child BMI and vocabulary at age 4 in a Norwegian cohort and the potential mediating contribution of breastfeeding duration. Methods: The Behavior Outlook Norwegian Developmental Study (BONDS) followed 1159 families and their children from 6 months of age onward. Parents reported on SES and breastfeeding duration in infancy, and child BMI and vocabulary ability were assessed at age 4. Direct and indirect effects were estimated using a path model that adjusted for several demographic and perinatal covariates (e.g., parental nativity and birthweight). Results: Family socioeconomic risk was significantly and negatively related to child vocabulary but was unrelated to child BMI. In addition, breastfeeding duration mediated the association between family socioeconomic risk and child vocabulary, with greater family socioeconomic risk associated with a shorter breastfeeding duration, which, in turn, predicted poorer child vocabulary. Conclusion: The current findings suggest that longer breastfeeding duration is a viable target for preventatively promoting child vocabulary, especially among families at socioeconomic risk.