MONDAY, June 20 (HealthDay News) -- Because millions of kids in the United States are affected by bullying, some people may shrug it off as just a part of growing up. But experts warn that it should be treated as a serious issue and not accepted as normal childhood behavior.

Estimates indicate that nearly 30 percent of U.S. teens -- or about 5.7 million -- have bullied someone, been targeted by bullies or both, according to the National Youth Violence Prevention Center.

Widespread use of the Internet has also taken bullying to a new frontier in online chat rooms, email and on social networking sites. Facing this growing problem, experts at Loyola University Medical Center in Maywood, Ill., warned that if bullying is not addressed head-on, this very real problem could do lasting harm to children's health and well-being.

"Being the target of a bully involves real suffering," Dr. Earlene Strayhorn, a child and adolescent psychiatrist at Loyola University, said in a university news release. "The constant stress of physical assaults, threats, coercion and intimidation can take a heavy toll on a child's psyche over time. The abuse may end at some point but the psychological, developmental, social and emotional damage can linger for years, if not a lifetime."

Because bullies thrive on intimidation and control, they often target those who are timid, passive and have fewer friends. They also choose victims who are younger, smaller and are less able to defend themselves. These victims may experience a number of adverse effects, including anxiety, fear and the inability to focus on schoolwork. Over time, Strayhorn noted, a bullied child's sense of self-esteem and self-worth can suffer, resulting in withdrawal, depression and insecurity.

"There have even been a number of instances in which victims have committed or attempted suicide in a desperate effort to find reprieve from bullying," said Strayhorn. "Some victims have violently struck back at their tormentors; in some cases targeting innocent bystanders."

Bullying differs from typical childhood teasing mainly because it is relentless, Strayhorn explained. Unlike more normal behavior among children, bullying can also include:

• Physical violence
• Coercion
• Name-calling
• Social ostracism
• Social isolation
• Verbal or written threats
• Murder or sexual assaults, which have occurred in extreme cases of bullying

Strayhorn advised parents who suspect their child is being bullied to take the following steps:

• Reassure bullying victims that they are not alone or at fault. Tell them that no one deserves to be bullied for any reason.
• If the bullying is occurring at school, meet with the appropriate school official and demand intervention to diffuse the situation.
• If the bullying is occurring outside of the school, tell children to seek safety in numbers and remain with friends or adults in the environment where bullying takes place.
• If the bullying has taken place over a length of time, consult a child or adolescent mental health professional to help your child develop coping strategies to deal with the situation.
• In extreme cases, contact the appropriate legal authorities.

More information

The American Academy of Pediatrics provides more information on bullying.