MONDAY, March 2 (HealthDay News) -- Post-traumatic stress disorder (PTSD) increases the risk of suicide in young adults, says a U.S. study of 1,698 participants who were tracked for 15 years after they started first grade in Baltimore public schools.

Interviews were conducted with the participants when they were young adults (average age 21) to assess the incidence of traumatic events, suicide attempts and the development of PTSD. Of the group, 1,273 had experienced a traumatic event, and 100 of those exposed to trauma (8 percent) developed PTSD.

Suicide had been attempted by 10 percent of those with PTSD, compared with 2 percent of the youths who experienced trauma but did not develop PTSD and 5 percent of those never exposed to a traumatic event.

The study was published in the March issue of the journal Archives of General Psychiatry.

"The mechanisms involved in the association between PTSD and suicide attempts are not known," wrote Holly C. Wilcox, of Johns Hopkins University School of Medicine, and colleagues. "There could be a common pre-existing predisposition to PTSD and suicide attempts that was present before the trauma occurred. Studies of early trauma and suicidal behaviors have implicated depression and impulsivity as possible mediators or possible pre-existing susceptibility traits."

They noted that previous research found that up to 20 percent of suicide attempts by young people can be attributed to sexual abuse during childhood.

"Although we did not focus explicitly on child sexual abuse, our results point to the need to base risk estimates of attempted suicide on data that take into account the psychiatric response to the trauma. By distinguishing between trauma-exposed persons without and with PTSD, we found that it is PTSD that is associated with an increased risk of a suicide attempt. Whether or not this finding applies to sexual abuse in childhood or adulthood should be investigated in future studies."

In 2005, suicide was the third leading cause of death among young people in the United States.

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