While bullying has been around for at least as long as there have been schoolyards, the phenomenon has gained much more attention, partly because of a number of high-profile suicides. Indeed, bullying has been linked to the idealization of suicide in many victims.

However, researchers say that bullying does not need to end in the suicide of a victim for it to have long-lasting consequences. A new study published in the Journal of Adolescent Psychology has found that a significant portion of bullying victims suffer from post-traumatic stress disorder, which can linger into adulthood.

When most people think of PTSD, they think of war or natural disasters, times of extreme tragedy. This study, published by Thormod Idsoe, Atle Dyregrov, and Ella Cosmovici Idsoe, found that about 33 percent of bullying victims suffer from PTSD. In addition, 40 to 60 percent of adults who have been bullying victims suffer from high levels of the signs of PTSD as well.

PTSD is defined by intrusive memories, avoidance behavior, and physiological stress activation, which is the reaction that the body has to stress. In children, these symptoms can have a disruptive effect on daily lives.

"Pupils who're constantly plagued by thoughts about or images of painful experiences, and who use much energy to suppress them, will clearly have less capacity to concentrate on schoolwork," Idsoe said in a statement. "Nor is this usually easy to observe - they often suffer in silence."

The researchers examined data from 963 14- and 15-year-old students. They found that girls were more likely to display symptoms of PTSD than boys were, even though boys were more likely to report being a victim of bullying. Their study found that 2.27 times more likely to report being a victim of frequent bullying; 27.6 percent of boys and 40.5 percent of girls had symptoms of PTSD.

Researchers are not sure why some victims of bullying reported PTSD while others did not. "We...found that those with the worst symptoms were a small group of pupils who, in addition to being victims of bullying, frequently bullied fellow pupils themselves," Idsoe said. "One explanation, for example, could be that difficult earlier experiences make the sufferers more vulnerable, and they thereby develop symptoms and mental health problems more easily."

Researchers found that, while many schools take bullying seriously and administer counseling to victims, many end counseling too early. Idsoe said that PTSD could persist for years in some children and that follow-up care is likely necessary.