The role of inflammation in the effects of peer victimisation and stressful life events on mental health in childhood

Background: Peer victimisation represents a salient stressor during childhood. However, studies investigating the mechanism of its impact on children’s mental health typically examine socio-cognitive factors as mediators. The current study sought to provide novel insight through testing a potential biological mechanism, inflammation. It also tested for pathway-specific effects by comparing how inflammation may mediate the effect of peer victimisation and that of another important stressor in childhood: adverse life events. Method: Data from 4,583 participants of the Avon Longitudinal Study of Parents and Children (ALSPAC) were used. Path analysis was carried out to investigate whether inflammation (IL-6 and CRP) at age 9 years mediates the effect of peer victimisation and stressful life events at age 8 years on internalising (peer and emotional) or externalising (hyperactivity and conduct) problems (measured at age 11 years), both before and after adjustment for potential confounders. Results: IL-6 partially mediated the effect of peer victimisation on peer problems, even after adjustment for potential confounders. Inflammation did not mediate the effect of stressful life events on either type of internalising problems. Neither stressor predicted externalising problems via inflammation. Conclusion: We did not find evidence that inflammation mediates the effect of stressful life events on mental health in childhood when they are considered alongside experiences of peer victimisation. Inflammation may already represent a form of biological embedding of peer victimisation in the early years