Hair cortisol as a biomarker of chronic stress: influence of school context and bullying

Background: Bullying has been identified as the most common form of aggression and the main source of stress during childhood and adolescence. The study aimed to analyze the effects of school context and bullying (victim, bully and bully/victim roles) as chronic stressors, using hair cortisol as a biomarker. Moreover, executive function was examined for its relationship with cortisol as well as its influence on bullying and academic skills. Method: The study included 659 eleven-year-old preadolescents from the INMA cohorts of Gipuzkoa and Sabadell. Bullying (Olweus Bully Victim Questionnaire) and variables related to the school context were used as stressors: perception of the school environment (Kidscreen-27 questionnaire), problems with peers (SDQ: strength and difficulties questionnaire) and academic skills (ad hoc questionnaire). Hair samples were used to measure cortisol levels. Additionally, executive function was evaluated using the Cups Task neuropsychological test. To test our hypothesis, structural equation modeling was conducted. Results: In this study, it was found that being a bully/victim in bullying situations is associated with higher hair cortisol concentrations (b=0.075; p=0.056). Additionally, higher hair cortisol concentrations were associated with worse executive functions across all models (victims: b=0.113; p=0.004; bullies: b=0.112; p=0.004; bullies/victims: b=0.112; p=0.004). Finally, having a poorer relationship with peers, a poorer perception of a school environment or lower academic skills did not affect hair cortisol levels (p>0.05). Conclusions: The present study examines the relationship between school context in general and bullying in particular with hair cortisol concentrations as an indicator of chronic stress for the first time. Despite concluding that the role of bully/victim appears to be related to hair cortisol concentrations, more research is needed to study this relationship.