War is hell, and for many of the U.S. veterans who served in the Vietnam conflict, the psychological nightmare rages on even 40 years after the last Marine left Saigon. Psychological surveys suggest that some 271,000 veterans of the war may still have full post-traumatic stress disorder, or PTSD. And for many vets, the PTSD symptoms are only getting worse with time.

“Roughly 11 percent of Vietnam veterans, over a 40-year period, continue to suffer from clinically important PTSD symptoms, either having the full diagnosis or very strong features of the diagnosis that interfere with function,” says study author Charles Marmar, director of The Steven & Alexandra Cohen Veterans Center at the NYU Langone Medical Center.

The latest study follows up on participants in the National Vietnam Veterans Readjustment Study conducted in the 1980s. According to Marmar, who co-authored the original report, the work serves a dual purpose in assessing the long-term affects of wartime trauma: “We owe it to the Vietnam generation, it's an amazing sacrifice that they made," he says. "But it's also the path ahead for the Iraq and Afghanistan generation, and we have to do better than we did for Vietnam.”

PTSD may be a relatively recent psychological concept, but historians are exploring its impact on soldiers from the American Civil War and even back to ancient Assyria circa 1300 B.C. Clinical symptoms include reliving events through nightmares or flashbacks, avoiding people or situations that might be reminders of traumatic events, negative changes in feelings toward oneself and others and a state of hyperarousal that makes it hard to concentrate or sleep and includes a common feeling of imminent danger.

Just over 1,800 participants of the original study were still alive when the followup was conducted between 2012 and 2013. Amazingly, 1,450 of those veterans participated again—nearly 80 percent of the initial cohort. The study assessed how many Vietnam vets suffered PTSD symptoms in four categories: re-experience and avoidance, withdrawal and numbing, arousal and emotional control and self-persecution or survivor guilt. Participants shared their experiences via a one-hour self-reported health questionnaire, a one-hour computer-assisted telephone interview and a three-hour clinical diagnostic phone interview.

“It tells you something very profound about the commitment of these veterans, who are now in their mid- to late-60s and still really wanted to tell their story,” says Marmar. “There is something very powerful in the social fabric of the American experience about Vietnam and how controversial Vietnam was, and maybe for these veterans the fact that many of them were unwelcome when they returned. For them it's very important to be able to tell their story now.”

The veterans symptoms were measured on the Mississippi Scale for Combat-Related PTSD, which Marmar calls “maybe the best measure ever developed to capture wartime PTSD-related symptoms and problems.” The responses showed that while 7.6 percent have seen significant decreases in their PTSD symptoms over the past decades, 16 percent had their symptoms become significantly worse. More than one-third of the veterans with current war-zone PTSD also suffer from major depression, according to the research, which appears this week in JAMA Psychiatry. Those categorized as improving or as getting worse experienced 20-point swings on the scale, which Marmar says is a sign of significant change.

The study can't yet explain why some veterans saw improvements with time while others deteriorated. Marmar and his colleagues are now trying to model a wide range of factors to attempt to explain what's at work in the minds of each group. “We're looking at things such as age at entry into the war—because some data suggest that being younger when you enter a war favors a more chronic or worsening PTSD pattern—education level at entry to the war, how many tours of duty were served, levels of war zone exposure, whether or not a soldier is injured in combat and whether someone was welcomed home favorably or unfavorably.”

Marmar suspects that aging is a potential factor that may lead to worsening symptoms. “Imagine someone home from three tours in Iraq who has three kids in the house and a demanding job, many responsibilities and an active social life. They've got a lot to pay attention to and a lot of distraction,” Marmar notes. “Fast forward to age 60-something when they may retire, their social supports may erode, their health gradually declines and they begin to face their own mortality. They don't have the same kinds of structures and responsibilities. More time to reminisce may not be helpful in this situation and may lead to an intensification or reactivation of trauma-related experiences in memory.”

Data from other studies suggest that roughly 70 percent of the men and women who've served in Iraq and Afghanistan do not develop major psychiatric problems. But work like the Vietnam vets study offers some lessons to better help those who do, Marmar adds.

“We can help them to identify these problems earlier, encourage them to seek care, de-stigmatize care and make services more affordable and accessible—including remote technologies like telemedicine and telemental health,” he stresses. Perhaps more important, he notes, is doing everything possible to help veterans protect their two main sources of social support—their families and those they served alongside. “Those two groups are more important than anyone else to protect their mental health over time.”