Patalay P, et al. - Using data on individuals from the Millennium Cohort Study, researchers conducted this longitudinal study to investigate body mass index (BMI) and internalizing symptoms from early childhood to midadolescence for comorbidity, codevelopment, and temporal precedence and to examine the sex differences and socioeconomic impacts in their association. For this analysis, they included data from 17,215 candidates with socioeconomic information in early childhood and BMI or internalizing symptoms during at least 1 assessment from 3 to 14 years of age. No connections were found between body mass index and internalizing symptoms in early childhood, between midchildhood and adolescence, however, relationships were seen in their codevelopment, with a higher probability of comorbidity. In middle childhood, the appearance of cross-domain temporal pathways implies that social, physiologic, and psychological processes start to have a progressively important role in these health outcomes. By targeting both childhood health outcomes, efforts to prevent and intervene early can be supported.