Bullying can trigger long-lasting effects on children by changing the structure of a gene that regulates serotonin, a neurotransmitter that affects mood and depression, according to a study by University of Montreal researchers. As they age, this can make the children more vulnerable to mental health problems.
"We knew from our previous studies that bullied children secrete less cortisol and had more problems with social interaction and aggressive behavior," said lead author Isabelle Ouellet-Morin, assistant professor of criminology at the university, by email. "But this study indicates that the reduction of cortisol is preceded by a [change in] serotonin." Cortisol is known informally as the "stress hormone" while serotonin is the "happiness hormone."
The study involved 28 pairs of 12-year-old identical twins enrolled in a longitudinal study at the King's College in London. One of each pair had been bullied, while the other had not. Because they are identical and raised in the same families, the changes in their genes could not be attributed to genetics or upbringing. The twins' hormone levels had been equal to their siblings' at age 5, before bullying occurred.
Previous studies have linked bullying victimization to academic difficulties, suicide, and behavioral and emotional problems. Her study helps understand the biology behind this, Ouellet-Morin said.
The next step, she said, is to study the twins at age 18, after the bullying is in their past, to measure their vulnerability to mental health problems. And, society should revisit its attitude toward bullying, she said.
"We need to stop thinking of bullying as a normative experience in adolescence," Ouellet-Morin said. "A growing body of research by our team and many others have shown that the consequences are real and sometimes quite severe."
The study is further evidence that "genes are not immutable," she said. "This shows that victimization in childhood changes not only our stress response but also the functioning of genes."
Although the naturalist Jean-Baptiste Lamarck (1744-1829) has long since been dismissed for his early-18th-century "inheritance of acquired traits" theory, Ouellet-Morin's research shows he was not totally off-track.
"His proposed mechanisms were wrong," Ouellet-Morin said. "But contemporary research shows that if maintained until the reproduction years, changes in [DNA] could, theoretically, be transmitted to a second generation."
The study was published in the December 2012 edition of the journal Psychological Medicine.