More violent behavior among young people are likely from a head injury sustained during their lifetime, according to an eight-year study from the University of Michigan School of Public Health.

In addition, the research found that young people, who suffered a recent head injury (within a year of being questioned for the study), were even more likely to report violent behavior. The researchers defined a head injury as having been knocked unconscious or sustaining a concussion or a fractured skull.

The report is one of the few studies to examine long-term effects of head injuries in a general population of young adults. Most other similar studies were conducted in prison populations. The research study appeared in the current issue of the journal Pediatrics.

Recently, there has been more media and research attention regarding youth, college and professional athletes who suffer head injuries and concussions while playing.

This study is broader, but confirms previous findings about the connection between violence and head injuries, said lead author Sarah Stoddard, a research assistant professor at the School of Public Health.

These are not necessarily sports-playing injuries. They could be from a car accident or from previous violent behavior, but it does support some of the sports research that's been going on with concussions, said Stoddard, who also is a research fellow at the University of Michigan School of Nursing.

Stoddard used data from the School of Public Health's Flint Adolescent Study, which looks at many issues regarding urban youth. Marc Zimmerman, professor of public health and chair of the University of Michigan Department of Health Behavior and Health Education, is the principal investigator of the study.

The researchers followed a group of ninth-graders from four schools in Flint, Michigan, into young adulthood. They conducted annual interviews over eight years. About 23 percent of participants, who were asked if they had ever sustained a head injury in fifth and sixth year, reported more violent behavior in the eighth year of the study.

Further, Stoddard and Zimmerman examined the proximal relationship between a head injury and violent behavior. They found that an injury reported in the seventh year of the study predicted violent behavior in the eighth year.

We found that the link between a head injury and later violence was stronger when a head injury was more recent, even after controlling for other factors including previous violent behavior, Stoddard said.

The results also suggest that adolescents and young adults, who have suffered a head injury that did not interfere with their ability to participate in an hour-long interview, may still experience significant adverse developmental or behavioral effects.

Traumatic brain injury is a serious public health issue, the researchers say. An estimated 1.7 million people annually sustain a traumatic brain injury, and that only includes people who get medical care, so the number is likely much higher.

Roughly 75 percent of head injuries are mild and many do not receive medical attention, but any traumatic brain injury disrupts the function of the brain. Long-term impact can include changes in cognition, language and emotion, including irritability, impulsiveness and violence.