Higher than average death rates among Vietnam War veterans with post-traumatic stress disorder (PTSD) suggest that combat trauma may still be affecting veterans' health even decades after the war, according to a new study.

U.S. veterans of the Vietnam War followed from the 1980s to 2011 were almost twice as likely to die during that period if they had PTSD compared to those without the disorder.

The findings can inform healthcare for Vietnam veterans, now mostly in their 60s and older, and prevention efforts for the next generation of soldiers, the study team writes in the American Journal of Epidemiology.

"The study offers really valuable empirical information that can help us better understand how to care for our Vietnam veterans . . . and also more recent veterans," said study author Nida Corry, of Abt Associates in Durham, North Carolina.

PTSD can develop after a person has been through a traumatic event like combat, child abuse or sexual abuse, terrorism attacks and other disasters, according to the Department of Veterans Affairs. Symptoms can include flashbacks, avoiding reminders of the traumatic events, changes in beliefs and activities and being overly alert, according to the VA.

A study published earlier this year estimated that more than 1 in 10 Vietnam war zone veterans still have PTSD or some symptoms of the disorder (see Reuters Health story of July 22, 2015, here: http://reut.rs/1NsyrVe).

Previous studies have also suggested that Vietnam vets - especially those who served in the war zone - are at increased risk of death, and that the added risk may be related to PTSD. However, those studies were often limited, according to the authors of the current study.

For the current study, the researchers from Abt Associates, New York University in New York City and other organizations analyzed information collected from 1987 to 2011 on nearly 2,400 Vietnam veterans, including 1,632 who served in the combat theater, which included Vietnam, Laos and Cambodia.

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Overall, about 9 percent of theater vets had PTSD at the time of the initial interviews in the 1980s, which was significantly higher than the 1 percent rate in vets who served outside the war zone.

About 16 percent of all Vietnam veterans who were alive in the 1980s are now dead, with most deaths due to cancer and heart disease, the authors estimate.

Male Vietnam War theater veterans who had PTSD were about 87 percent more likely to die between 1987 and 2011 than those without the condition - even after adjusting for demographic, social and economic factors.

"What we found is that having PTSD was associated with a greater risk of death from cancer and external causes," Corry said, such as traffic accidents, suicide, murder and other accidental injuries.

Male and female veterans who were exposed to high levels of stress in the war zone - but not necessarily diagnosed with PTSD - were also at increased risk of death during the study period, the researchers found.

The combination was even deadlier. Veterans with high levels of war zone stress exposure who developed PTSD were at the greatest risk of death, Corry said.

The study can't explain why PTSD and war zone stress raise the risk of death, but the explanation is likely complex, said Alan Peterson, a PTSD researcher from The University of Texas Health Science Center at San Antonio.

For example, he said, PTSD may create a consistent level of stress in the body - like a false alarm for impending danger - that eventually affects different organ systems throughout the body.

"There is this physiological arousal that in theory affects all organ systems and that's going to wear over time," said Peterson, who was not involved in the new study.

The study authors point out that Vietnam vets still make up the majority of living veterans, so it's important to keep studying the long-term mental and physical health effects of their wartime experiences and to understand how they might interact with the aging process.

Corry said findings like these - and other analyses of the same data - may provide an opportunity to provide better care for veterans through earlier screenings and treatments.

"This is sort of the best data we have to foreshadow those long term needs," she said.