Child Maltreatment and Mental Health in Middle Childhood: A Longitudinal Study in Japan.

Toxic stress caused by child maltreatment can lead to adverse mental health outcomes in later life, yet unmeasured confounding has been a major issue in many previous studies. To examine the association between child maltreatment and resilience and behavior problems among early elementary school-age children, we used data from a population-based longitudinal survey targeting all first-grade children in 2015 in Adachi City, a ward in Tokyo, Japan. Children whose caregivers provided valid responses during the 2015 (first grade; ages 6-7 years), 2016 (second grade; ages 7-8 years), and 2018 (fourth grade; ages 9-10 years) waves of the study were included in the analysis (n = 2,920). Fixed-effects regression models revealed that child maltreatment was inversely associated with resilience (ß = -0.89, 95% confidence interval (CI): -1.05, -0.72) and prosocial behavior (ß = -0.03, 95% CI: -0.05, -0.003) and positively associated with behavior problems (ß = 0.32, 95% CI: 0.27, 0.37) over 4 years of follow-up (2015-2018), after controlling for all time-invariant confounders and measured time-varying confounders and survey year. These associations were consistent across sex. Child maltreatment may hamper the development of resilience and prosocial behavior and induce behavior problems in early elementary school children over time. Future researchers should identify modifiable protective factors for better mental health among maltreated children.