Researchers have known that bullying can take a psychological toll on both bullies and victims, but it's been unclear just how long those effects would last.
One report published earlier this month found bullying targeting lesbian, gay and bisexual youth contributed to their feelings of depression and worthlessness as young adults.
In the new study, depression and anxiety tied to bullying at school persisted at least through people's mid-twenties. Worst off were those who had been both bullies and targets of bullying, according to findings published Wednesday in JAMA Psychiatry.
"It's obviously very well established how problematic bullying is short-term," said William Copeland, a clinical psychologist who led the new study at Duke University Medical Center in Durham, N.C.
"I was surprised that a decade down the road after they've been victimized, when they've kind of transitioned to adulthood, we would still see these emotional marks for the victims and also the bullies/victims."
His team's research included 1,420 youth from Western North Carolina who were asked about their experiences with bullying at various points between age 9 and 16, then were followed and assessed for psychiatric disorders through age 26.
Just over one-quarter of kids and their parents
After adjusting for the participants' history of family hardships, the researchers found that, compared to young adults with no history of bullying, former victims were at higher risk for a range of psychiatric conditions.
For example, 6 percent of uninvolved youth went on to have an anxiety disorder, versus 24 percent of former bullying victims and 32 percent of youth who had been both bullies and targets of bullying.
Kids who originally reported both bullying and being bullied were the most likely to be diagnosed with panic disorder or depression as young adults or to consider suicide.
"It's not surprising that that would be the case, because in part they're reacting to the trauma of being bullied and they also carry with them the experience of having bullied," said Dr. Mark Schuster, chief of general pediatrics at Boston Children's Hospital and a professor at Harvard Medical School, who wasn't involved in the new research.
"These folks are the ones who get bullied and instead of experiencing empathy … they're more reactive and they see bullying as more of a way of getting attention," Copeland told Reuters Health.
Youth who were just bullies and never picked-on themselves were at four times higher risk for antisocial personality disorder, which is characterized by a lack of empathy and mistreatment of others.
Psychiatric disorders in childhood and kids' family problems were tied to bullying but didn't fully explain future problems, Copeland and his colleagues found. Some of the adult disorders seemed to stem from the bullying itself, they said.
The study "calls attention to just how serious bullying can be, and it reinforces what we've been learning, which is that bullying is not just a rite of passage, it's not just part of growing up and all kids experience it and they're stronger for it," Schuster told Reuters Health.
"From everything we understand at this point, it can have serious long-term consequences."
Researchers said schools, parents and doctors need to work together to try to prevent bullying in the first place.
But for kids who have experienced bullying, Schuster said a supportive adult can go a long way toward preventing future psychological consequences.
"In part they need an adult who can help them navigate this, who can help put an end to the bullying and can create a safe haven for them," he said.
"Having to keep the secret that you're bullied and not having anyone to turn to for advice and support makes it that much harder."