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Bullying by childhood peers leaves a trace that can change the expression of a gene linked to mood.

The Office of Juvenile Justice and Delinquency Prevention defines bullying among children as repeated, negative acts committed by one or more children against another.

Bullying could be verbal or physical, and these days, there are an increasing number of reports of cyber bullying as well. This negative act is not only limited to children; a good number of adults experience bullying at the workplace too. Various studies have been conducted around the world to understand the impact of bullying on victims and its long-term effects.

While earlier studies have listed the affects of bullying from long-term health issues to anxiety and depression in victims, a new study suggests that bullying by peers changes the structure surrounding a gene involved in regulating mood, making victims more vulnerable to mental health problems as they age.

The study, conducted recently by a researcher at the Centre for Studies on Human Stress (CSHS) at the Hôpital Louis-H Lafontaine and professor at the Université de Montréal, was aimed at better understanding the mechanisms that could explain how difficult experiences disrupt our response to stressful situations.

"Many people think that our genes are immutable; however this study suggests that environment, even the social environment, can affect their functioning. This is particularly the case for victimization experiences in childhood, which change not only our stress response but also the functioning of genes involved in mood regulation," lead author of the study Isabelle Ouellet-Morin said.

Another study conducted previously by the same researcher showed that children who were victims to bullying secrete less cortisol - the stress hormone - but had more problems with social interaction and aggressive behavior.

The current study suggests that reduction of cortisol, which occurs around the age of 12, is preceded two years earlier by a change in the structure surrounding a gene (SERT) that regulates serotonin, a neurotransmitter involved in mood regulation and depression, the report says.

For the study, the researchers recruited 28 pairs of identical twins, all of them around 10 years of age, and analyzed them separately on the basis of their experiences of bullying by peers.

"Since they were identical twins living in the same conditions, changes in the chemical structure surrounding the gene cannot be explained by genetics or family environment. Our results suggest that victimization experiences are the source of these changes," says Ouellet-Morin.

According to the author, it would now be worthwhile to evaluate the possibility of reversing these psychological effects, in particular through interventions at school and support for victims.

The study was published in the journal Psychological Medicine.