While most of the media coverage of post-traumatic stress disorder (PTSD) focuses on the rough transition home experienced by veterans of Operation Enduring Freedom in Afghanistan and Operation Iraqi Freedom in Iraq, the disorder has been experienced by veterans from earlier conflicts, dating back to World War II, as well as a number of civilians.

By studying veterans from the Vietnam War, researchers are able to see the long-term consequences of having PTSD on a person's health. A new study says male twin veterans with PTSD who served during the Vietnam War are twice as likely to develop heart disease during a 13-year period, compared to those without PTSD.

The study, funded by the National Institutes of Health, looked into the presence of heart disease in 340 identical twins and 222 fraternal twins from the Vietnam Era Twin Registry. They found that the incidence of heart disease was 22.6 percent in twins with PTSD (177 veterans) and 8.9 percent in those without PTSD (425 veterans).

"This study provides further evidence that PTSD may affect physical health," said Dr. Gary H. Gibbons, director of the NIH's National Heart, Lung, and Blood Institute.

The researchers also found that among the 234 twins where one brother had PTSD and the other didn't, the incidence of heart disease was almost double, with 22.2 percent of those with PTSD compared to 12.8 percent of those without.

The study focused on twins because it allowed the researchers to control for influences of genes as well as the environment when it came to how heart disease and PTSD developed. People with heart disease included anyone who had a heart attack, an overnight hospitalization for heart-related symptoms, and anyone who had any kind of procedure on their heart. They were also able to see the reduced blood flow to the heart in veterans with PTSD using nuclear scans.

"This study suggests a link between PTSD and cardiovascular health," Dr. Viola Vaccarino, lead researcher and chair of the department of epidemiology at the Rollins School of Public Health, said. "For example, repeated emotional triggers during everyday life in persons with PTSD could affect the heart by causing frequent increases in blood pressure, heart rate, and heartbeat rhythm abnormalities that in susceptible individuals could lead to a heart attack."

The emotional triggers in PTSD are caused by anxiety from traumatic events a person has seen or experienced — in this case the Vietnam War — and can happen at any moment. People with PTSD experience a "fight-or-flight" response even when they are no longer in danger. Symptoms often include flashbacks, frightening thoughts, depression, avoidance, being easily startled, and having angry outbursts.

The disorder affects almost 7.7 million adults in the U.S., and according to a 2006 analysis of military records from the National Vietnam Veterans Readjustment Study, 15 to 19 percent of Vietnam veterans experienced PTSD at some point after the war. With regards to the Iraq and Afghanistan conflicts, of the 1.7 million soldiers who served, 20 percent have been diagnosed with PTSD.

The Department of Veterans Affairs tracked veterans from Iraq and Afghanistan who were diagnosed with PTSD and mild traumatic brain injury, and found signs of heart disease, diabetes, slowed metabolism, and obesity among the young veterans — all of which are more common illnesses in middle to older age adults.

"Future research to clarify the mechanisms underlying the link between PTSD and heart disease in Vietnam veterans and other groups will help to guide the development of effective prevention and treatment strategies for people with these serious conditions," Gibbons said.

Source: Vaccarino V, et al. Post-traumatic stress disorder and incidence of coronary heart disease: a twin study. Journal of the American College of Cardiology. 2013.