LOS ANGELES — The U.S. military has faced two epidemics over the last decade of war in Afghanistan and Iraq.
One is suicide. The annual rate of military personnel taking their own lives has doubled to about 20 per 100,000. That translated to a record 324 suicides in the Army last year.
The other is concussion, also known as mild traumatic brain injury, or TBI. The proliferation of roadside bombs has subjected thousands of troops to brain-rattling explosions.
Several studies have suggested a link between the two epidemics — that service members who suffered concussions are at greater risk for suicide.
A paper published this week in the journal JAMA Psychiatry helps illuminate the nature of that relationship. Researchers found that military personnel in Iraq who suffered multiple concussions were far more prone to suicidal thoughts than those who sustained just one such injury or never had a concussion.
And by controlling for depression and post-traumatic stress disorder — well-known risk factors for suicide — the study moves closer to establishing TBI as a significant factor in suicides.
Craig Bryan, the lead author of Wednesday’s study, was an Air Force psychologist deployed in Iraq in 2009 to assess and treat TBI. His study is based on 157 military personnel and four civilian contractors who were referred to his clinic for suspected concussions.
Most of the 161 subjects were men in the Army. They were assessed for TBI and questioned about their history of head trauma, depression, PTSD and suicidal ideation.
A statistical analysis was used to establish the relationship between the number of concussions and suicide risk.
Of the 18 subjects who had never suffered a concussion, none reported having had suicidal thoughts in the previous year. Among the 58 with one concussion, 3 percent said they had considered suicide. The rate among those with two or more concussions was 12 percent.
“All of a sudden the likelihood of being suicidal increased dramatically once you had the second head injury,” said Bryan, now head of research at the University of Utah’s National Center for Veterans Studies.
Though some of the subjects in the study had suffered five or more concussions in their lifetimes, Bryan said their risk of suicide was no higher than for those with two such injuries.
How a concussion might increase the risk of suicide remains poorly understood. Mild TBI can impair problem-solving skills and the ability to function socially, and some researchers believe that those deficits increase the likelihood that somebody will consider suicide when faced with certain stressful situations.
While the new study suggests that TBI directly contributes to the risk, it is far from definitive. Another possible explanation for the link is that a character trait — impulsiveness — is driving both phenomena.
It is a well-established risk factor for suicide. And as Bryan pointed out, it also increases the likelihood of suffering a concussion. “Somebody impulsive is more likely to act without foresight and get injured,” he said.
More studies are needed to determine cause and effect, he said.
Also, it is likely that some patients in the study were less than truthful about their medical and psychiatric histories. Studies suggest that troops are reluctant to acknowledge problems that might sideline them.
“They very much want to be returned to duty,” Bryan said. “They feel guilty letting everybody else down while they are in a clinic.”
Some studies have estimated that up to 20 percent of the troops deployed to Afghanistan or Iraq have suffered a concussion. While those caused by bomb blasts have received the most attention, many have also occurred in various accidents outside combat.
The long-term effects of concussions have become a pressing research topic in recent years as a result of the wars. Emerging evidence from football, ice hockey and other contact sports has also shown that repeated injuries may pose a cumulative danger.