The finding is based on roughly two decades spent tracking the bullying histories of 1,420 young people from childhood into early adulthood.
"We've been exploring the long-term consequences of bullying for a while," noted study lead author William Copeland, an associate professor in the department of psychiatry and behavioral sciences at Duke University Medical Center in Durham, N.C.
"At first, that meant looking at the low-hanging fruit, such as the emotional and behavioral impact. But then we decided to look beneath the skin a little bit, to see what, if anything, is going on," he added.
"And what we found is that, in terms of inflammation, the victims of childhood bullying are the worst off as adults -- even after accounting for many other factors. On the other hand, bullies were actually the best off, indicating that physically, in some ways, they are the healthiest of all," Copeland said.
The surprising results came from blood tests for C-reactive protein (CRP) levels, which as they increase are known to signal a higher risk for a number of health complications, including heart disease and metabolic syndrome. Metabolic syndrome is the name for a group of risk factors that raise the risk for heart conditions and other problems including diabetes and stroke.
While CRP levels rose among all the participants over time, those who had been bullied had the highest CRP levels by the time they were in their early 20s, the researchers found. Those who were a victim and instigator of bullying had adult CRP levels equivalent to those with no bullying history at all. The lowest CRP levels were seen among former bullies.
Copeland and his colleagues published the findings online May 12 in the Proceedings of the National Academy of Sciences.
The team's analysis focused on data collected by the Great Smoky Mountains Study, which enrolled mostly white North Carolina children at the ages of 9, 11 and 13.
Until the children reached the age of 16, bullying histories were recorded via parental interviews -- 83 percent of the time involving the mother. Then, when they were between 19 and 21, the interviews were conducted directly with the participants.
The findings held even after accounting for other factors, such as body mass index (a measurement based on height and weight), drug use, overall physical and mental health status, and exposure to other types of childhood traumas.
Why the lower CRP levels in those who bullied? The study authors theorized that bullies may have gained a boost in social status as children that in turn conferred a boost in physical health as adults.
"It's extraordinarily rare to see a childhood experience persist as a physical consequence among adults, but the potency of our findings is clear," Copeland said.
"It's not that this means we should encourage kids to become bullies," he added. "But it does suggest that the biological impact of bullying may be similar to that of physical abuse, sexual abuse or neglect, which -- to me -- is very striking."
Bruce Simons-Morton, associate director for prevention at the U.S. National Institute of Child Health and Human Development in Bethesda, Md., called the study "reasonably novel."
"There has been a lot of research into the social and psychological consequences of bullying and victimization," he noted. "And we pretty well understand by now that persistent victimization leads to a lot of negative development outcomes. But this is particularly interesting, because it finds that there's also a physiological relationship," Simons-Morton said.
"But we have to be careful to say that what we're finding here are associations between bullying and physical affects," Simons-Morton added. "They looked at a relatively large sample of people, and did so for lengthy period of time. But their findings are still not necessarily causal."
What the study clearly does, he said, "is raise a lot of interesting questions that will need to be explored with additional research."
For more on bullying, visit the U.S. Department of Health and Human Services.