School children who are bullied are more than twice as likely to think about killing themselves and to make suicide attempts as their peers who aren't bullied, according to a new analysis.
Researchers also found that cyberbullying, such as harassment over the Internet, was more closely linked to suicidal thoughts than in-person bullying.
"We found that suicidal thoughts and attempted suicides are significantly related to bullying, a highly prevalent behavior among adolescents," Mitch van Geel told Reuters Health in an email.
Van Geel is the study's lead author from the Institute of Education and Child Studies at Leiden University in the Netherlands.
He said it's estimated that between 15 and 20 percent of children and teens are involved in bullying as the perpetrator, victim or both.
"Thus efforts should continue to reduce bullying among children and adolescents, and to help those adolescents and children involved in bullying," he wrote.
While previous studies have found links between bullying and suicidal thoughts and attempted suicides, less is known about whether the association differs between boys and girls. Also, fewer studies have examined the role of cyberbullying.
For the new analysis, published in JAMA Pediatrics, the researchers searched databases for previous studies published on bullying.
They found 34 studies that examined bullying and suicidal thoughts among 284,375 participants between nine and 21 years old. They also found nine studies that examined the relationship between bullying and suicide attempts among 70,102 participants of the same age.
Overall, participants who were bullied were more than twice as likely to think about killing themselves. They were also about two and a half times more likely to attempt killing themselves.
In one study included in the analysis, for instance, researchers found that about 3 percent of students from New York State who were not bullied thought about or attempted suicide. That compared to 11 percent of students who were frequently bullied.
The extra risk of suicidal thoughts and suicide attempts tied to bullying was similar among participants of different age groups and among boys and girls.
Suicidal thoughts were more strongly linked to cyberbullying than to traditional bullying, but the researchers caution that this finding is based on data from only a handful of studies.
"At this point, this is speculative and more research is definitely needed on cyberbullying," van Geel wrote.
It could be, however, that cyberbullying victims feel belittled in front of a wider audience and may relive the attacks because they are stored on the Internet, he added.
"I think it fits with a literature that's been around for some time that suggests the kids who are worse off are the kids who can't escape from bullying," William Copeland told Reuters Health.
Copeland, who was not involved with the new study, has researched bullying at the Duke University School of Medicine in Durham, North Carolina.
He cautioned that the studies included in the analysis can't prove bullying caused suicidal thoughts or suicide attempts. It could be, for example, that kids who attempt or think about suicide are more likely to be bullied.
Copeland said there are an increasing number of school-based programs aimed at preventing bullying.
"I don't think we know quite as much about targeting kids who have been bullied and preventing those suicidality behaviors," he added.
Copeland said parents can ask their kids about how things are going and whether anyone is giving them problems at school or online to help the children open up about bullying.
"Some people have the assumption that bullying is a part of growing up, that bullying is relatively harmless, or even that it may build character," van Geel wrote.
"There are now meta-analyses that demonstrate that bullying is related to depression, psychosomatic problems and even suicide attempts, and thus we should conclude that bullying is definitely not harmless," he added.