Veterans with post-traumatic stress disorder may have more to worry about than a debilitating psychiatric condition.
In research published this week in the Journal of the American College of Cardiology, scientists studying a group of male twins who served in the military during the Vietnam era - 1964 to 1975 - found that a diagnosis of PTSD more than doubled the likelihood that they would go on to develop heart disease.
It wasn't just that veterans with PTSD smoked more and exercised less, though they did. The Emory University researchers controlled for those and other influences on cardiovascular health.
The 281 twin pairs in the study were selected from a 30-year-old government research project called the Vietnam Era Twin Registry.
Some had been to Vietnam, while others had never left the United States.
All 562 men had been assessed for PTSD in 1992; 137 of them were found to have it.
None had reported having heart disease when they joined the registry between 1987 and 1992.
Between 2002 and 2010, the researchers evaluated them again for heart disease.
Among the men with PTSD, 22.6 percent had suffered a heart attack, undergone a heart procedure or spent at least a night in the hospital for heart trouble - compared with 8.9 percent of men without the anxiety disorder.
Sophisticated scans showed that the men with PTSD also had less blood flow to heart tissue.
The researchers compared 117 pairs of twins in which one brother had the disorder and the other did not. They found that 22 percent of the men with PTSD had heart disease, compared with only 12.8 percent of their twin brothers.
In other words, being related - and sharing genetic material and, usually, upbringing - narrowed the gap only slightly.
Genetics, in fact, were found to play no role: The gap was the same whether the brothers were identical twins - thus sharing all their DNA - or fraternal ones, who shared half of their DNA.
Something else has to be driving the relationship between PTSD and heart disease, said Dr. Viola Vaccarino, the epidemiologist who led the study.
"People with PTSD are known to have higher levels of stress hormones," she said.
"The repeated activation of the stress system may have adverse effects on the cardiovascular system."