Stress system reactivity moderates the association between cumulative risk and children's externalizing symptoms.

This study examined children's stress system reactivity via the autonomic nervous system (ANS) and hypothalamic pituitary adrenal axis (HPAA) during an acute stressor as moderators of predicted relations between cumulative risk (CR) and mental health symptoms in a sociodemographically diverse sample of young children (n = 58). We employed a reliable stressor paradigm to allow assessment of individual differences in respiratory sinus arrhythmia (RSA) and pre-ejection period (PEP), indexing ANS reactivity, and salivary cortisol, indexing HPAA reactivity. Children's behaviours were assessed using the Child Behaviour Checklist (CBCL). Cumulative risk was indexed by eight parent-reported sociodemographic and psychosocial risk factors. There was a significant main effect of CR on externalizing but not internalizing behaviours. Significant moderations emerged showing that among children with high CR, less RSA withdrawal during the acute stressor and less cortisol recovery following the stressor were associated with to greater externalizing behaviours. Among children with low CR, RSA and cortisol recovery were unrelated to internalizing or externalizing symptoms. Cortisol and PEP reactivity were not significant moderators. Results highlight the relevance of stress system function for understanding differential susceptibility to the early emergence of externalizing symptoms, linked to cumulative risk exposure.