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 Mage = 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 (β12 = .13; β23 = .12; β34 = .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.