Why are so many American soldiers killing themselves? The answer is more complicated than PTSD from war. According to the largest study ever undertaken focusing on suicide rates in the military, suicide rates among soldiers in Iraq and Afghanistan more than doubled from 2004 to 2009, with more than 30 suicides per 100,000. But the rate among those who never deployed was even higher, tripling to between 25 and 30 per 100,000 people. What's going on?

"A simple explanation that war is hell and you send people to war and bad things happen to those people is an incomplete explanation," says Michael Schoenbaum, the lead author on the study. Researchers at the National Institute of Mental Health studied the records of nearly a million soldiers. (Perhaps that’s a big enough number to quiet the naysayers, including the Army general who blogged about suicide being selfish.) The research published as three separate papers in The Journal of the American Medical Association Psychiatry.

The report found significant rates of mental illness among soldiers. Around a quarter of troops reporting having some form of psychiatric disorder, and one in 10 have multiple mental health issues. Suicide rates were reported highest among men and deployed women, white servicemembers, those who are junior in rank, and those who are recently demoted. Previous deployment was also a significant factor.

Suicide rates have historically been lower in the military, because recruiting tends to weed out some at-risk people (like elderly men, for example, who have a higher suicide rate than the population at large). That changed in 2008, when the number of military suicides surged ahead. The suicide rate for civilians of similar age and demographics to the Army has remained relatively level at around 19 per 100,000 people. But during the last decade of war, that's changed. In 2013, the Department of Veterans Affairs released the startling figure that 22 veterans were killing themselves every day, or one soldier every 65 minutes.

But the study's author's suggest that the recruitment process might not be screening people effectively. One-third of post-enlistment suicide attempts are associated with mental health problems that existed before enlisting in the Army, which also suggests restricted access to guns and other means of suicide. Further, two trends in the Army for recruitment and retainment purposes that were previously thought to have increased the risk of suicide were also debunked as being factors in military suicides. The trends, the use of waivers and “stop-loss,” were found to make no difference in the rate of suicide. Waivers are used to relax qualifications for new soldiers, whether that’s due to lack of education or conduct record, and “stop-loss” is forcing soldiers to remain in service past the end of their deployment.

“Mental disorders are leading causes of US military morbidity," the report says. "Indeed, health care visits and days out of role owing to mental disorders in the US military are exceeded only by those owing to injuries. This is partly because selection and retention criteria lead to low rates of chronic physical disorders, but military service also has unique stressors that can increase mental disorders."

The number of hospital days due to mental health disorders also doubled for U.S. military members between 2006 and 2010. The report says that most mental disorders develop in childhood and adolescence, and are too mild to lead to rejection from the military, despite the fact they they could lead to more severe episodes in the future.