Bullies may enjoy health benefits that last into adulthood from their behaviour, researchers said. And in turn, children who are bullied can suffer long-lasting inflammation.
"Our study found that a child's role in bullying can serve as either a risk or a protective factor for low-grade inflammation," William Copeland, one of the researchers and an associate professor of psychiatry and behavioral sciences, said. "Enhanced social status seems to have a biological advantage." Lest readers think researchers are suggesting children be raised to be bullies, Copeland, of Duke University School of Medicine in the US state of North Carolina, added: "However, there are ways children can experience social success aside from bullying others."
The work was published online in the Proceedings of the National Academy of Sciences.
Researchers used the Great Smoky Mountains Study, which has gathered information from 1,420 people from 11 North Carolina counties for more than 20 years. The researchers looked at a marker of inflammation called C-reactive protein. The participants were interviewed and provided blood samples.
C-reactive protein is affected by conditions such as poor nutrition, lack of sleep and infection. "But we've found that they are also related to psychosocial factors," Copeland said.
The researchers looked at victims, "pure" bullies and children who were both. Bullying involves repeatedly mistreating another person to improve or retain one's status.
Earlier studies have shown that victims of bullies suffer socially and emotionally into adulthood, including increased depression and anxiety. Such children, the researchers said, also report physical problems such as pain and susceptibility to illness.
But, the study said, little is known about how the experience of being bullied is "biologically embedded to influence health status". One potential mechanism is chronic, low-grade inflammation.
In adults, a high social status, including income or education level, is associated with lower levels of inflammatory markers, the researchers wrote.
"The finding of lower increases in [C-reactive protein] levels for pure bullies into adulthood is novel," the researchers said, adding that previous work tended to focus on the those who struggled through adversity.