Researchers already know that many kids who are bullied appear to suffer socially, psychologically and even physically years later. According to a new study, the physical consequences might be explained by an increase in low-grade inflammation throughout the body.

Kids who are bullied tend to be sick more often than their peers and may have stomach aches, sleep problems and headaches and lose their appetites, researchers write in the journal PNAS. In the new study, bullied kids had higher inflammation levels as young adults than their uninvolved classmates.

“We’re pretty confident that this is a bullying effect,” said William Copeland, who led the study at Duke University School of Medicine in Durham, North Carolina.

Inflammation might explain the connection between bullying and physical health, Copeland told Reuters Health.

An increase in inflammation could lead to health problems like heart disease down the line, he said.

The authors followed 1,420 kids from age nine to 21, interviewing the kids and their mothers along the way about bullying involvement and taking blood samples from the kids every year or two.

They measured the level of C-reactive protein, a marker often used to gauge body-wide inflammation levels, in the blood samples.

The marker can be affected by any number of stressors or changes in the environment, like lack of sleep or psychological problems, Copeland said.

C-reactive protein levels went up for all kids as they got older, but kids who had been repeatedly bullied saw more of an increase in inflammation than a group that was not involved at all in bullying.

The more often kids reported being bullied, the more the inflammation marker increased over time.

“We’ve known for a number of years that a variety of early life traumas ranging from sexual and physical abuse to mental abuse and neglect lead to a variety of bad health outcomes in just about every area of health that you want to measure,” said Dr. Andrew H. Miller, a psychiatrist at Emory University School of Medicine in Atlanta, Georgia.

One of the “common denominators” in many ills like cancer and heart disease is inflammation, he told Reuters Health.

“The idea that bad things happening to you leads to inflammation has been what we are beginning to think may be the link between bad events early in life and bad health outcomes later,” said Miller, who wasn’t involved in the new study.

The elevated levels of C-reactive protein in victims of bullying indicate they might have a three- to four-fold increased risk of developing heart disease or diabetes, Miller said. But to know if that connection is going to pan out, researchers would have to wait until the participants entered their 40s or 50s.

“The kids that we’re looking at, none of them yet have cardiovascular disease,” Copeland said. “Whether the levels they’re displaying suggest that they’re going to get heart disease, we have to follow them later to see that.”

The study also found that kids who were bullies but were never bullied themselves had less of an increase in inflammation over time than the group of kids not involved in bullying in any way.

“That’s a difficult finding to work with,” Copeland said. “You don’t want to encourage folks to bully.”

“Bullying is a way of enhancing social status and achieving success,” he said. “There are other ways people can enhance social status or success without wreaking havoc on others.”

Miller cautioned against deciding bullies come out ahead in the long run when the inflammation measure only ran to young adulthood.

“I wouldn’t put a lot of stock in that one,” he said. “Life teaches many lessons that occur after 21.”

Kids with the highest levels of inflammation were the ones who had experienced bullying repeatedly over a long period of time, or in multiple settings, Copeland said.

Parents and caretakers should deal with the potential long-term effects of bullying only after stopping the bullying from taking place, he said.

“The obvious answer for all of this is to prevent it from happening,” Copeland said, and that’s a difficult goal even with the many comprehensive anti-bullying campaigns in effect in schools.

“You don’t treat the child without getting them out of the traumatic experience first,” he said.

SOURCE: PNAS, online May 12, 2014