Bidirectional associations between mental health problems and language ability across 8 years of childhood.

Research examining the development of behavior, emotions and language, and their intertwining is limited as only few studies had a longitudinal design, mostly with a short follow-up period. Moreover, most studies did not evaluate whether internalizing symptoms and externalizing symptoms are independently associated with language ability. This study examines bidirectional associations between internalizing symptoms, externalizing symptoms and language ability in childhood in a large, population-based cohort. Longitudinal data from the Millennium Cohort Study, a cohort of children in the United Kingdom followed from birth to 11 years (n = 10,878; 50.7% boys), were analyzed. Internalizing and externalizing symptoms were based on parent reports. Language ability (higher scores reflecting poorer ability) was assessed by trained interviewers at ages 3, 5, 7 and 11 years. Structural Equation Models (SEM) were performed, including random-intercept cross-lagged panel models (RI-CLPM) and cross-lagged panel models (CLPM). Internalizing symptoms, externalizing symptoms and language ability were stable over time and co-occur with each other from early life onwards. Over time, externalizing symptoms in early childhood were associated with less growth in language skills and with increases in internalizing symptoms. In late childhood, language ability was negatively associated with later internalizing and externalizing symptoms. The early start, co-occurrence and persistent nature of internalizing symptoms, externalizing symptoms and (poorer) language ability highlights the importance of comprehensive assessments in young children who present problems in one of these domains. Specifically, among children in the early grades of elementary school, those with language difficulties may benefit from careful monitoring as they are more likely to develop difficulties in behavior and emotions.