A tour of duty in Afghanistan or Iraq — even one involving combat — does not increase a service member's risk of suicide, according to a study that tracked more than 150,000 troops for up to eight years.
The study, published Tuesday in the Journal of the American Medical Assn., challenges the common assumption that the stresses of being in a war zone and exposure to the horrors of battle are behind a sharp increase in the military's suicide rate over the last decade.
"People have said, 'Of course it's multiple deployments, it's the length of deployments, it's combat. That's a no-brainer,'" said Matthew Nock, a Harvard University psychologist and suicide expert who was not involved in the study. "But that appears not to be the case."
The study found that those most likely to take their own lives were men who had reported a history of mental health troubles.
Traditionally, screening of recruits, health and fitness standards and access to medical care have given service members a suicide rate that was about half that of their civilian peers.
But since the wars began with the invasion of Afghanistan in late 2001, the military has essentially caught up. Last year, there were 524 suicides among active-duty service members, reservists and National Guard members, according to data compiled by The Times.
The biggest rise occurred in the Army and Marines from 2005 to 2009.
The new analysis relied on data from the Pentagon's largest-ever attempt to measure the effects of war on military personnel. Known as the Millennium Cohort Study, the project began enrolling subjects in 2001 and surveying them about their mental health and other aspects of their lives. The study plans to track them through 2068.
The suicide researchers, led by Cynthia LeardMann, an epidemiologist at the Naval Health Research Center in San Diego, followed subjects who enrolled from 2001 to 2007, and used death records to identify suicides through the end of 2008. Of the 151,560 people in the study, 83 took their own lives.
The analysis found that men were twice as likely as women to commit suicide. Depression also doubled the risk, and alcohol abuse more than doubled it.
The suicide rate for service members who never went to war; those who went but did not see combat; and those who witnessed death, abuse or maiming were statistically the same.
The number or length of deployments had no bearing on the risk. Nor did the researchers see any bump in the suicide rate among veterans who had recently left the service, a transition period that some experts have worried is particularly difficult and dangerous.
Researchers had no clear reason why the suicide rate has been increasing.
LeardMann speculated that the general stresses of wartime — regardless of where a service member is stationed — might be behind a rise in psychological problems, which in turn is fueling the increase in suicide.
Other experts have suggested that people who volunteer for service during war may be more likely to have preexisting mental illness.
A recent Times article looking at suicides among service members who never deployed to war zones found several cases in which recruits were struggling with the direction of their lives and joined the military in search of purpose.
Some outside experts cautioned that more time might be needed to see the full psychological effects of the wars and that deployment might still be a factor in suicide among some segments of the military.
"It may be that severe, repeated combat exposure does play a role for a small subset of war fighters," David Rudd, a psychologist and director of the National Center for Veterans Studies, a collaboration between the University of Utah and the University of Memphis, said in an email.
He noted that the study used a broad definition of combat exposure and did not attempt to parse suicide risk by the intensity of what service members had experienced.
Dr. Timothy Lineberry, a psychiatrist and suicide expert at the Mayo Clinic in Rochester, Minn., said the study, in one respect, was good news. "The things we see associated with suicide outside the military are the same things we see associated with suicide in the military," he said.
That suggests that identifying and treating depression and alcohol abuse could prevent suicides, he and others said.
Over the last few years, the military has expanded its treatment options and encouraged service members to seek help. Those efforts, however, have not decreased the suicide rate.