Decades after the end of the U.S. war in Vietnam, more than one in ten American veterans from the conflict still experience at least some symptoms of post traumatic stress disorder (PTSD), according to a new study.

One third of veterans with PTSD also suffer from major depressive disorder, the research team reports in JAMA Psychiatry.

For some of these aging veterans, mounting health problems and declining cognitive function can exacerbate PTSD, as can the social isolation that often accompanies retirement, said lead study author Dr. Charles Marmar, chairman of psychiatry and director of the veterans’ center at New York University Langone Medical Center.

“All of these make it more difficult to suppress and control traumatic memories,” he said by email.

To assess PTSD, Marmar and colleagues followed up with 1,450 Vietnam veterans who had participated in a study in the 1980s assessing their quality of life about ten years after the end war.

For the current study, researchers mailed questionnaires and conducted phone interviews to assess four aspects of PTSD: re-experiencing and avoidance, withdrawal and numbing, arousal and emotional control and self-persecution or survivor guilt.

Almost 11 percent of the war zone veterans had either full-blown PTSD or at least some symptoms that impacted their daily lives, researchers estimated. That compares with roughly 15 percent in the 1980s.

PTSD from any cause, including for veterans who didn’t fight in the war zone, afflicted about 12 percent of men and 8.5 percent of women, the researchers found.

Based on this representative sample of vets, the authors conclude that roughly one in four Vietnam war zone veterans alive today have experienced PTSD or some symptoms of the condition at some point in their lifetime.

The study highlights the need to diagnose and treat not just PTSD, but also what’s known as sub-threshold PTSD, or symptoms that impair daily life without meeting the current clinical definition of full-blown disease, Dr. Charles Hoge, author of an editorial accompanying the study and a senior scientist at Walter Reed Army Institute of Research.

“The study confirms what we know from several decades of PTSD research and clinical care – that war-zone PTSD can at times have a chronic and even lifelong impact,” Hoge said by email. “The most important take-home message for Vietnam veterans is that there are many more treatment options available now than when they returned from Vietnam, and it’s never too late to receive treatment.”

For some Vietnam veterans, PTSD may be particularly acute because they lacked social support when they returned home from war, said Dr. Alan Peterson, a psychologist at the University of Texas Health Science Center in San Antonio who specializes in combat-related PTSD.

“Our nation turned its back on many of our Vietnam veterans after they were involuntarily drafted into service,” Peterson said by email. “It has been a long and uphill road to recovery for many of them.”

Depression, while common in the elderly, may be even more common among Vietnam veterans, particularly if they have PTSD and avoid many activities that might also make them happy such as having intimate relationships and friendships and enjoying leisure activities such as sports or going to the movies, he added.

Signs that veterans have PTSD can include withdrawal from family and friends, inability to get restful sleep, deterioration of work or school performance, rage behavior, excessive use of alcohol or drugs, engaging in risky behaviors or talking about suicide, Hoge said.

Treatment for PTSD can include a combination of medication and psychotherapy, Hoge said.

“It has been suggested that no one comes home unchanged after a deployment to a war zone,” Peterson said. “However, most will naturally recover over time, especially with support of friends and family who are willing to talk with them about their experiences and encourage them to gradually get back into the normal routine of life.”