The word "bully" may conjure up images of a 9-year-old punk shaking down a 7-year-old for lunch money. But teenagers experience bullying too, and research shows it can be a red flag for depression and suicidal behavior.

That's true whether teens are doing the bullying, or are victims of it.

"If you are vulnerable and being bullied, it can be the straw that breaks the camel's back," said Madelyn S. Gould, a professor of psychiatry and public health at Columbia University and the New York State Psychiatric Institute who has studied bullying.

That doesn't mean bullying causes suicide. But it is an associated factor. Six teenagers were charged recently in South Haley, Mass., in connection with the case of Phoebe Prince, who killed herself after she complained of being tormented by kids in her high school.

Ann Haas, director of suicide prevention projects at the American Foundation for Suicide Prevention, cautioned against thinking in terms of "cause and effect" when it comes to bullying and suicide. "The key risk factor for suicide in youth is unrecognized, untreated mental disorders, particularly depression," Haas said.

But a study of 2,342 high school students published in 2007 in the Journal of American Academy of Child and Adolescent Psychiatry showed "a clear association" between bullying, depression, suicidal thoughts and suicide attempts, according to Gould, who was one of the authors.

NEGATIVE IMPACTS

Among students who said they were frequently bullied in school, nearly 30 percent reported depression, and 11 percent reported serious thoughts of suicide and suicide attempts.

Among those who frequently bullied others in school, almost 19 percent reported experiencing depression and about 8 percent reported suicidal thoughts or attempts.

In contrast, among kids who said they were never bullied, only 7 percent reported depression, and 3 percent reported suicidal thoughts or suicide attempts.

Overall, the study found about 9 percent of high school students said they were frequently bullied, and 13 percent said they frequently bullied others. These rates were consistent with other studies, the researchers said.

Teens are often secretive about their social lives, but bullying is "something we need to ask our kids about," Gould said.

Remind them that insulting or humiliating someone on Facebook, by text or e-mail can be just as devastating as physical confrontations or pranks.

"In the 21st century electronic age, you can be one step removed from what you're doing," Alec L. Miller, an adolescent psychologist at the Children's Hospital at Montefiore/Albert Einstein College of Medicine in New York. "You're not actually saying something to someone's face.

"You're just writing an e-mail. That makes it a lot easier to bully and harass. We've had bullying for centuries, but this is a new phenomenon."

Miller believes that trash-talk on TV — from the critiques on "American Idol" to in-your-face insults on reality shows — has desensitized us to the harm words can inflict.

"There's a level of mean-spiritedness" that has come to be accepted, he said.

Explain that bullying — whether physical or verbal — "is serious, that it's not in fun, that some people take this very seriously and they can think of hurting themselves," Gould said.

SPEAKING OUT

Encourage kids to take action if they witness bullying. A simple comment like "Cut it out" or "Leave him alone" could help change the dynamic when someone's being picked on.

"Everyone needs to take responsibility for what's happening in the school," Miller said.

Yet teens may fear becoming the bully's next target if they speak out. So be sure to encourage them to tell parents, teachers or guidance counselors, and if you're the one they come to, let school officials and other parents know what's going on.

Despite the popular conception that the social world of every high school in America is run by "mean girls," Gould's research found that rates of bullying behavior — both for victims and perpetrators — were about twice as high among boys as among girls.

Other gender differences: Physical bullying is more prevalent among boys and "relational" bullying — teasing, verbal harassment and social manipulation — is more common among girls. But while girls involved in bullying were far more likely to report depression, suicidal thoughts or suicide attempts than boys, boys both involved in bullying in some way or not involved are four times as likely as girls to die by suicide, Gould said.

Haas added that teens struggling with sexual identity issues may be especially vulnerable to bullies.

Gould said a new study awaiting publication followed adults who reported being bullied in high school to see if it had any lasting impact.

The good news: Most adults who were bullied in high school "were not suicidal, not depressed and not at risk for suicide," she said.

"There is life after high school," Haas said, "but that can take many years for all of us to appreciate."