Body mass index and internalizing symptoms from early childhood through early adolescence: Trend of codevelopment and directionality

Background Higher body mass index (BMI) and internalizing symptoms often codevelop with each other, and both of them have been widely linked to child later maladjustment. However, existing studies on the association between BMI and internalizing symptoms predominantly focus on the between-person association (i.e., the average association for a given group) and use continuous measures of BMI. To address these gaps, using approaches that can effectively partition within-person from between-person variation, this study aimed to delineate temporal dynamics (i.e., directionality) of the associations between BMI and internalizing symptoms (as continuous and clinical cut-off categorical measures for both of them). The trend of codevelopment between BMI and internalizing symptoms is also investigated. Methods This study used data from the Early Childhood Longitudinal Studies, Kindergarten Class of 2010-2011 (ECLS:2011), a nationally representative birth cohort study in the United States. Participants were 17,552 children (48.78% female, M-age = 5.6 years old at the first wave) who were assessed seven times from kindergarten through Grade 5. Results Results of the random intercept, cross-lagged panel model suggested reciprocal within-person associations between BMI and internalizing symptoms from child 7.1 to 11.1 years old. Conclusions Our findings highlight both the necessity of disaggregating between-person and within-person effects in cross-lagged associations between BMI and internalizing symptoms and the importance of interventions that target body weight and mental health issues in middle childhood to reduce the negative impact of both in the long run.