The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.

It is still not clear how the experience of being bullied in childhood translates into long-lasting health problems. A new US study has found that victims of bullying have high levels of a protein in their bloodstream that is associated with fighting off an infection – even into early adulthood. This finding may help understand further the association between childhood bullying victimisation and poor health outcomes later.

Research has consistently shown that young victims of bullying show difficulties including symptoms of anxiety, depression and also conduct problems and psychotic symptoms. These problems related to children’s mental health can persist even after the bullying has stopped, sometimes up until mid-life.

There are some hypotheses that bullying victimization is a form of “toxic stress” that can have an impact on physiological responses to childhood adversity. In turn, these responses may help explain why some victims develop health problems.

Mental and physical health problems are often related and although young children are generally healthy, research has started to show that bullied children tend to become adults with health problems.

One such mechanism is the inflammatory response, measured by the release in the bloodstream of a protein called C-reactive protein (CRP). High levels of CRP is a generic response that indicates that the body is either fighting an infectious agent, reacting to an injury or responding to a chronic condition such as arthritis.

Research has shown that CRP can also be elevated among people who experienced maltreatment by an adult in their childhood. This suggests that the body reacts in a similar way to “toxic stress” as it does to an infection.

Bullying as a ‘toxic stress’

Knowing that bullying is associated with high levels of CRP is important for two reasons. First, it would provide further support that childhood bullying victimization should be considered as a toxic stress alongside other forms of abuse including child maltreatment. Second, this would provide a novel lead for identifying new targets for various types of interventions aimed at reducing problems related to the experience of being bullied in childhood.

The new findings from the longitudinal Great Smoky Mountains Study of 1,420 children in the US has looked at CRP levels in children involved in bullying as victims, bullies and bully-victims (participants who both bully others and were also bullied). The authors, led by William E. Copeland at Duke University Medical Center, tested whether study participants who were bullied between the age of nine and 16 showed high levels of CRP in adolescence, and also later in early adulthood.

Their results indicate that the participants who experienced several exposures to bullying had higher levels of CRP compared to participants who were not involved in bullying – either as victims, bullies or bully-victims.

These associations remained even after taking into account the participants' prior CRP level and variables associated with CRP levels such as body mass index, medication and alcohol use. They also took into account variables linked to being involved in bullying, including maltreatment, family dysfunction, and anxiety disorders.

Lasting into early adulthood

The authors then looked at CRP levels as the study participants entered adulthood. They observed a similar pattern of findings: victims of bullying had higher levels of CRP compared to those who were not involved in bullying. Furthermore, participants who were repeatedly bullied showed the highest levels of CRP.

Surprisingly, participants who bullied others showed the lowest levels of CRP in early adulthood amongst all four groups of children examined in this study. These associations also remained after the researcher controlled for prior CRP, variables associated with CRP levels and variables associated with being involved in bullying.

We already know from previous research that being bullied in childhood “gets under the skin” and can influence other mechanisms in the body involved in the physiological responses to stress, such as the hypothalamic-pituitary-adrenal axis. For example, bullied children show a blunted level of cortisol response – a hormone released under stress – when exposed to stress in a laboratory experiment.

A study of identical twin pairs where one twin had been bullied but the other not has shown that while non-bullied twins had a normal increase of cortisol after experiencing a social stress laboratory, their bullied co-twins showed a blunted response. And the more severe and frequent the bullying, the lower the cortisol response.

The new Duke research on the inflammatory process adds to a growing body of evidence that demonstrates that we need to move away from the perception that bullying is harmless and part of normal growing up. Instead, bullying should be considered as another form of toxic stress with potentially profound effects on mental and physical health. These effects have been repeatedly observed in childhood and increasingly so in adolescence and in adulthood too.

Louise Arseneault does not work for, consult to, own shares in or receive funding from any company or organization that would benefit from this article, and has no relevant affiliations.

This article was originally published on The Conversation. Read the original article.