Being bullied raises the blood's level of C-reactive protein, or CRP, a marker of systemic inflammation and a risk factor for cardiovascular and other diseases.
Scientists followed 1,420 boys and girls ages 9 to 21, interviewing bullies, victims and their parents. They assessed CRP levels with periodic blood tests.
After controlling for initial levels of CRP and for many factors that affect it — sex, age, race and various health and socioeconomic issues — the researchers found that CRP levels in victims increased in direct proportion to the number of bullying incidents they experienced.
Bullies, in contrast, had low increases in CRP, even lower than those in children not involved in bullying at all. The finding suggested that a bully's increased social status might have biological advantages, the scientists said. Their study was published online on Monday in The Proceedings of the National Academy of Sciences.
"The only other kind of social adversity where we see this kind of long-term effect is in children who are physically abused or neglected," said the lead author, William E. Copeland, an associate professor of psychiatry at Duke.
Image: Bullied boy, via Shutterstock