Childhood bullying has been linked to a number of physical and mental health effects, including lower self-worth, depression, and serious illnesses later in life. But until now, researchers had largely focused on examining these effects in victims of abuse, not the bullies themselves. This may soon change, as a long-term study published today in Proceedings of the National Academy of Sciences was able to demonstrate that "pure bullies," people who have never experienced bullying themselves, do in fact face a long-lasting health effect from abusing others. As it turns out, that effect is actually beneficial — even when compared to people who aren't involved in bullying at all.

"Pure bullies had the lowest blood levels of C-reactive protein (CRP), a marker for inflammation," says William Copeland, an epidemiologist at Duke University and co-author of the study. "This is kind of a beneficial outcome," because CRP is a risk factor for a variety of health problems down the road, such as cardiovascular disease and metabolic syndrome, Copeland says. These findings therefore suggest that "the bullying experience was protective for the bullies."

In the study, researchers tracked over 1,000 children living in western North Carolina over seven years. They interviewed these kids multiple times starting at age nine, and then returned to interview them again in their early 20s. During each interview the scientists took blood samples, and asked participants a number of questions, including if they had experienced bullying over the course of the last three months. This allowed researchers to see and analyze changes in CRP levels over time, starting even before the bullying occurred.

"Some people ask, ‘Well aren't the victims more frail to begin with?'" Copeland says. "But we know that that's not the reason for these results because we can really isolate these other things on later CRP levels and account for any sort of behavior problems before the children were bullies or victims." The results, he says, are clear. "We're still seeing these lower levels [in bullies]."

As expected, Copeland adds, the victims had the highest levels of CRP. Interestingly, however, people who were both bullies and victims as children did not experience a positive or negative inflammatory effect. "They fell right in line with what folks were uninvolved in bullying have," Copeland says. This means that their experiences might be canceling each other out. That's especially surprising, Copeland says, because previous studies have found that "bully-victims" actually have the worst outcomes in terms of mental health.

The researchers aren't sure what causes these changes in CRP levels, but previous studies have suggested that stressors such as bullying and childhood maltreatment might affect how the body responds to stress in the long run. "There may be a dysregulation of our internal stress response system," Copeland says, "such that because of the experiences of bullying, cortisol gets revved up too often and too early in childhood." Cortisol is an anti-inflammatory stress hormone, and if it gets over-excited repeatedly and for long periods at a time, the body's stress-response system essentially "burns out," leaving the body vulnerable to inflammation.

But pure bullies, Copeland says, don't experience this kind of stress. In fact, they often experience increased social status. "Obviously this doesn't mean that we are encouraging kids to go out and bully others," Copeland says. "There are many other ways to achieve that besides wreaking this havoc on other people, like athletics, clubs, social activities."

The researchers caution, however, that high CRP levels don't necessarily mean that a person is in poor health. Rather, the marker is "a nice index of future health risk in people who are in their 20s and 30s."

Andrea Danese, a developmental psychobiologist at King's College London who did not participate in the study, said in an email to The Verge that "this new study is a helpful addition to the literature in showing that these effects extend to another important childhood stressor, namely bullying." Danese is part of a team of researchers who found similar effects in adults who experienced childhood maltreatment and social isolation at a young age. But Danese was unsure about how to interpret the results regarding the protective effects of bullying others. "The results about the protective effects of being a pure bully are less clear," he said, and "less supported by collateral information."

Copeland and his team are, for now, focused on analyzing the rest of the data they collected. They also plan to keep studying the study's participants, to find out more about the how these increased CRP levels might translate into serious health problems later in life. "It can't be overemphasized," he says, "how extraordinary it is to see these effects so long down the road."