Examining systemic inflammation as a pathway linking peer victimization to depressive symptoms in adolescence.

Background: Adolescents exposed to victimization are at an increased risk for a variety of adverse mental health outcomes, including depressive symptoms. Yet, the biological pathways underlying these associations remain poorly understood. Focusing on within-person processes, we examined whether low-grade systemic inflammation mediated the longitudinal associations between peer victimization and depressive symptoms in adolescence.

Methods: 207 adolescents (at baseline M = 12.69 years; SD = 0.49; 43.5% female) participated in a multi-wave longitudinal study, with assessments repeated every 6 months over 1.5 years. At each assessment wave, participants self-reported their peer victimization experiences and depressive symptoms. Dried blood spots were collected at each wave using a finger prick procedure to assay a key marker of low-grade systemic inflammation, interkeukin-6 (IL-6). Data were analyzed using random-intercept cross-lagged panel models.

Results: The cross-lagged paths from IL-6 to depressive symptoms were significant across all models and waves (β = .13; β = .12; β = .08), indicating that when adolescents' levels of low-grade systemic inflammation were above their person-specific average, they reported increased levels of depressive symptoms in the subsequent months. However, no significant cross-lagged within-person associations emerged between peer victimization and either IL-6 or depressive symptoms.

Conclusions: The findings provide no evidence for the hypothesized mediating role of inflammation in the within-person associations between peer victimization and depressive symptoms. Nevertheless, they extend prior research by indicating that elevated levels of low-grade systemic inflammation predict the development of depressive symptoms in adolescence.