A new study of veterans from the Vietnam War has troubling implications for troops who fought much more recently — in Afghanistan and Iraq.

The study suggests that 40 years since the Vietnam War ended, hundreds of thousands of those vets still struggle every day with mental health problems linked to the traumas they experienced. It was published in the latest issue of JAMA Psychiatry.

"This study is officially called the National Vietnam Veterans Longitudinal Study," NPR's Daniel Zwerdling reports.

Daniel says that researchers have been studying Vietnam veterans longer than they've studied any other soldiers. Congress ordered the studies to be done to understand how war affects soldiers over most of their lives.

The good news they found is that between 70 and 75 percent of the Vietnam veterans they've studied have never suffered from mental illness linked to war — no PTSD, depression, alcoholism or drug addiction.

Charles Marmar of NYU's medical school, who led the latest look at nearly 2,000 veterans, says that the lack of mental illness "doesn't mean they haven't been affected by their experience. For sure, to go to war is a profound experience and changes you forever in many ways, but they didn't break down with psychiatric illness."

But there's bad news, too: "Roughly 11 percent of the vets they studied are in serious trouble," Daniel says. "They still suffer from PTSD, or from a disorder like it. That's around 10 times the rate among veterans who didn't serve in Vietnam. The Vietnam vets still get flashbacks, they're irritable, depressed, they can't sleep well."

Many "are quite alienated from family and friends, and have trouble either in the workplace or in their family environments," says Marmar.

When you extrapolate those findings, Marmar says more than 250,000 vets still struggle every day. He says that if the results of the Vietnam veterans study bears out for current troops, society should expect similar numbers with these problems 30 to 40 years from now.

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