New research provides evidence of a connection between childhood peer victimization, inflammation, and peer problems. The findings, published in Brain, Behavior, & Immunity – Health, suggest that heightened inflammation plays a role in the link between bullying and social difficulties.
Childhood bullying, a pervasive issue that affects many children, has long been recognized as a significant stressor during the formative years. Prior research has shown that peer victimization can lead to a range of negative outcomes, including poor mental health and social difficulties. However, this new study sought to delve deeper into the underlying mechanisms that link bullying experiences to these adverse consequences.
The motivation behind this research stems from the need to better understand the specific ways in which peer victimization affects children’s mental health. While previous studies have explored socio-cognitive mechanisms that contribute to the impact of bullying, such as hostile attributions and poor coping strategies, the role of biological processes, particularly inflammation, had largely been overlooked. To address this gap in knowledge, the researchers aimed to investigate whether inflammation mediated the effect of peer victimization on mental health in childhood.
“I have a long-standing interest in the effect of adverse experiences on child cognition and mental health, and the role of inflammation in explaining some of that effect. My previous research has established a link between stressful life events, inflammation and child mental health but in this study we wanted to explore the specific role of a very salient childhood life stressor: peer victimisation,” said study author Eirini Flouri, a professor of developmental psychology at University College London and director of the CUBIC Lab.
The study drew from the Avon Longitudinal Study of Parents and Children (ALSPAC), an ongoing cohort study based in the UK. The research team utilized data from a substantial sample of children, totaling 4,583 participants, to examine the relationship between peer victimization, stressful life events, inflammation, and mental health.
At the heart of the study were detailed measures of peer victimization and stressful life events during middle childhood (around ages 7-8) and assessments of inflammation at age 9. Peer victimization was assessed through a child-reported Bullying and Friendship Interview Schedule, which included questions about overt victimization (such as physical violence or teasing) and relational victimization (such as spreading rumors or excluding the victim from social groups). Stressful life events were measured using a checklist completed by mothers, covering a variety of potentially upsetting events experienced by the child.
The researchers focused on two key markers of inflammation: interleukin 6 (IL-6) and C-reactive protein (CRP). Blood samples were collected from participants at age 9, and IL-6 and CRP levels were measured through laboratory assays. These markers provided insights into the participants’ inflammatory response, a crucial component of the study.
“We compared the effects of overt peer victimization (at age 8 years) with those of general stressful life events (measured with a checklist of 17 life stressors) at that age on mental health (emotional symptoms, peer problems, conduct problems, hyperactivity) at the end of primary school (age 11 years),” Flouri explained. “We then tested if inflammation (measured with IL-6 and CRP at age 9 years) explained those effects. We used data from a large birth cohort study in the United Kingdom, so our findings pertain to the general child population.”
The researchers confirmed that peer victimization, especially overt victimization, had a significant impact on children’s mental health. Children who experienced peer victimization, particularly in the form of overt bullying, were more likely to encounter social difficulties and exhibit internalizing problems, such as emotional issues and peer relationship problems.
The most notable discovery was the partial mediation of the effect of overt peer victimization on peer problems by interleukin 6 (IL-6). In simple terms, IL-6 played a role in explaining why some children who were bullied experienced difficulties in forming relationships with peers. This suggests that inflammation may be a biological mechanism through which bullying affects social development.
“We did not find evidence that inflammation explains the effect of stressful life events on mental health in childhood when they are considered alongside experiences of overt peer victimization,” Flouri told PsyPost. “However, inflammation explained part of the effect of peer victimization on a mental health difficulty, peer problems. Inflammation may already represent a form of biological embedding of overt peer victimization in the early years. If these links are causal, they suggest that inflammation may be biologically embedding the effects of peer victimization, resulting in long-term difficulties interacting and integrating with others.”
Interestingly, the study found that while IL-6 played a role in mediating the impact of overt peer victimization on peer problems, it did not mediate the effect of stressful life events on mental health. This highlights the specificity of inflammation as a mediator in the context of bullying, indicating that not all childhood stressors operate through the same biological pathways.
“Our study showed that overt peer victimization had a larger effect than exposure to stressful life events on peer problems, and that this effect was partially mediated by IL-6,” Flouri explained. “Importantly, the indirect effect of overt peer victimization via IL-6 was robust to adjustment for other stressors experienced during childhood in addition to several potential confounding factors, but it was also very specific: inflammation could only explain part of the effect of overt peer victimisation only on peer problems.”
“This outcome specificity was somewhat surprising. Stressful life events were, as expected, related to mental health problems in children, but when considered alongside overt peer victimisation they did not have an indirect effect on mental health via inflammation. This was unexpected. Together, these findings indicate that, when exposure to stressors in childhood is comprehensively considered, inflammation may have a very specific role in explaining the effect of specific stressors on specific mental health outcomes in children in the general population.”
While IL-6 partially mediated the effect of peer victimization, it’s essential to note that the mediation effect was relatively small. This suggests that other factors, beyond inflammation, also contribute to the relationship between bullying and social difficulties. However, the mediation effect remained robust even after accounting for confounding factors and other stressors experienced during childhood.
Like any scientific study, this research has its limitations. It’s crucial to recognize that this study is observational, and thus, it cannot establish causality. While the findings suggest a potential link between peer victimization, inflammation, and mental health outcomes, more research is needed to confirm causation.
“Inflammation was not related to externalizing problems at all,” Flouri added. “But then again, this was not unexpected for us. We are now expanding some of the work on peer victimization and inflammation, and the preliminary findings are very interesting, so watch this space!”
The study, “The role of inflammation in the effects of peer victimisation and stressful life events on mental health in childhood“, was authored by Ellie Roberts, Marta Francesconi, and Eirini Flouri.
