Nearly 1 in 5 U.S. soldiers had a common mental illness, such as depression, panic disorder or ADHD, before enlisting in the Army, according to a new study that raises questions about the military's assessment and screening of recruits.

More than 8% of soldiers had thought about killing themselves and 1.1% had a past suicide attempt, researchers found from confidential surveys and interviews with 5,428 soldiers at U.S. Army installations.

The findings, published online in two papers in JAMA Psychiatry, point to a weakness in the recruiting process, experts said. Applicants are asked about their psychiatric histories, and those with certain disorders or past suicide attempts are generally barred from service.

"The question becomes, 'How did these guys get in the Army?'" said Ronald Kessler, a Harvard University sociologist who led one of the studies.

A third study looked at the increased suicide rate among soldiers from 2004 to 2009. The study, which tracked nearly 1 million soldiers, found that those who had been deployed to Afghanistan or Iraq had an increased rate of suicide.

But it also found that the suicide rate among soldiers who had never deployed also rose steadily during that time. The study did not explain the cause.

The Pentagon did not make officials available to discuss the studies.

The three studies are the first from a massive research initiative started in 2009 by the Army and the National Institutes of Mental Health in response to the surge in suicides.

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