Various physical and psychological forms of development take place during the transition from childhood to adolescence, including the onset of puberty, delayed sleep-wake behavior patterns, and increases in internalizing symptomatology. Theory suggests that pubertal processes influence the onset of internalizing symptoms, and this association may differ between boys and girls. The contextual amplification hypothesis suggests that pubertal development interacts with contextual or dispositional factors to impact risk for psychopathology. Family stress and peer stress are two critical factors during early adolescence that have potential moderating effects on the association between pubertal development and internalizing symptoms. In line with the biopsychosocial framework, the current study examined various psychosocial (e.g., family stress, peer stress) and biological (e.g., sleep, genetics) factors that may have effects on the puberty-internalizing relation. Participants were a racially/ethnically and socioeconomically diverse sample of twins who were part of an ongoing longitudinal study (N=818 children; Arizona Twin Project; Lemery-Chalfant et al. 2019). The current study examined the association between puberty and internalizing symptoms, with stress (i.e., family, peer) as potential moderators, and sleep indicators (i.e., objective and self-reported sleep) as potential mediators. Behavior genetic analyses explored the moderated heritability of family stress on internalizing symptoms. Findings revealed that greater pubertal development predicted higher internalizing symptoms in boys, but not girls. For girls, peer stress interacted with pubertal development to predict internalizing symptoms, but simple slopes were not significant. Sleep indicators were not significant mediators between pubertal development and internalizing symptoms for boys or girls. Univariate twin models revealed environmental influences on internalizing symptoms, and both genetic and environmental influences on peer stress. Family stress did not significantly moderate the genetic and environmental influences of internalizing symptoms.

Stress in individuals presents in various forms and may accumulate across development to predict maladaptive physical and psychological outcomes, including greater risk for the onset of internalizing symptoms. Early life stress, daily life experiences, and the stress response of the hypothalamic-pituitary-adrenal (HPA) axis have all been examined as potential predictors of the development of psychopathology, but rarely have researchers attempted to understand the covariation or interaction among these stress domains using a longitudinal design when looking at the influence of stress on internalizing psychopathology. Further, most research has examined these processes in adulthood or adolescence with much less attention given to the influence of these dynamic stress pathways in childhood. Guided by the biopsychosocial model of stress, this study explored early life stress, daily life stress, diurnal cortisol (cortisol AM slope), and internalizing symptoms in a racially/ethnically and socioeconomically diverse sample of twins participating in an ongoing longitudinal study (N=970 children; Arizona Twin Project; Lemery-Chalfant et al. 2013). An additive model of stress and a stress sensitization framework model were considered as potential pathways of stress to internalizing symptoms in middle childhood. Based on a thorough review of relevant literature, it was expected that each stress indicator would individually predict internalizing symptoms. It was also predicted that early life stress would moderate the associations between diurnal cortisol and internalizing symptoms, as well as daily life stress and internalizing symptoms. Multilevel modeling analyses showed that early life stress and cortisol AM slope, but not daily life stress, predicted internalizing symptoms. Early life stress did not moderate the associations between daily life stress and internalizing symptoms or cortisol AM slope and internalizing symptoms. Results support independent additive contributions of both physiological stress processes and early life parental stressors in the development of internalizing symptoms in middle childhood. Future investigation is needed to better understand the sensitizing effects of early parental life stress during this developmental stage.