The study could also have implications for other people, like football players, who get multiple TBIs commonly known as concussions.
"The idea for this actually came from people in the general public. It was a question that was asked a lot," said Bryan. "No one has ever looked at this notion of multiple TBIs."
U. researchers used a database created in 2009 after they studied 161 military personnel stationed in Iraq and evaluated for a possible TBI in 2009.
They found one in five 21.7 percent of service members who had suffered more than one traumatic brain injury had ever entertained thoughts of suicide. For those with one such injury, the portion dropped to less than 7 percent, and down to nothing for those who didn't have a TBI.
When they were asked about suicidal thoughts over the short term, or previous year, the results were similar: 12 percent of those with multiple injuries had thought about taking their own lives, compared with 3.4 percent of those with one injury and zero for those with none.
Up next are more detailed studies on the effects of the injuries, and studying what interventions work to prevent suicide in the long run. Researchers studied the patients during a six-month period as service members thought to have suffered a TBI were referred to an outpatient clinic at a combat support hospital in Iraq. Diagnosis was made by a clinical psychologist; soldiers with moderate to severe injury were evacuated and not included in the research.
For the study released Wednesday, patients were divided into three groups and studied based on the number of similar injuries they had suffered.
A traumatic brain injury is caused by a bump, blow or jolt to the head or a penetrating injury that disrupts the normal function of the brain. It is considered the "signature injury" of the Iraq and Afghanistan conflicts due to the prevalence of improvised explosive devices and other similar weapons.