In the United States more than one in four children are exposed to weapon-related violence, either as a victim or witness. Now, a new study has found that this exposure increases their risk for issues with mental health.

Using data from a 2011 national survey of children and parents, researchers were also able to estimate that 1 in 33 children have been assaulted in incidents where lethal weapons such as guns and knives were used. This type of exposure increases the likelihood that they will arm themselves or associate with people who carry weapons. They are also more likely to suffer long-term psychiatric consequences, the study authors say.

"Exposure to violence involving highly lethal weapons is associated with higher trauma symptoms, over and above exposure to all other types of violence, making it a strong contributor to adolescent depression, anxiety and aggression," says study coauthor Kimberly Mitchell, a research assistant professor of psychology at the University of New Hampshire's Crimes Against Children Research Center. "These are problems pediatricians encounter often in their practices."

Researchers also found that children that are exposed to weapon-related violence are also more likely to experience seven or more types of victimization in the prior year.

The study, published online in the journal Pediatrics, focused on more than 4,100 children from age 2 to 17 who participated in a telephone survey. For children under the age of 10, the parents or caregivers answered the questions.

From these responses, researchers estimated that more than 17.5 million children have experienced violence that involved weapons such as guns, knives, rocks and sticks. However, exposure to lethal weapons had the strongest consequences. Researchers also discovered that, to a child, simply witnessing an incident involving a lethal weapon was as traumatic as being the victim.

"Our data -- not just in this paper but the whole National Survey of Children's Exposure to Violence research program -- shows that witnessing violence has just as many traumatic psychological consequences for kids," says study coauthor Sherry Hamby, a research professor of psychology from Sewanee University of the South.

"After all, just because the gun was pulled on someone else doesn't mean the witnesses aren't in danger, too," Hamby says. "And sometimes what someone might describe as 'witnessing' involves actual physical danger or injury to kids as well."

"We found youth living in what we're calling a 'weaponized environment' are more likely to report victimization with a weapon," Mitchell says.

The study, however, does not suggest that simply being exposed to guns and knives increases the risk of being traumatized. It is being exposed to violence using guns and knives that causes the trauma.

"Positive firearm experiences for some youth may moderate or buffer the effects of victimization exposure," the authors of the study say.