More proof on the toll that stress takes is provided by studies of people with post-traumatic stress disorder (PTSD).

It’s long been known that people with PTSD are at higher risk of suffering from heart disease, or having a heart attack or stroke.

But further research on PTSD sufferers has added to our understanding of the damage stress does to the heart.

Just this year, researchers from the U.S. Department of Veterans Affairs, reporting on a study of more than 8,000 veterans living in Hawaii and the Pacific Islands, found people with PTSD had a nearly 50 percent greater risk of developing heart failure over a seven-year follow-up period.

In addition, whether it led to a PTSD diagnosis, combat service was itself a strong predictor of heart failure.

Veterans with combat experience were about five times more likely to develop heart failure than those who had not seen combat.

Why does PTSD cause these heart risks?

In seeking an explanation, another group of researchers found evidence that PTSD leads to overactive nerve activity, dysfunctional immune response, and activation of the hormone system that leads to increased blood pressure.

But they also discovered that cardiovascular events — including stroke and heart attack — could be stressful enough to cause PTSD symptoms.

This puts those patients at greater risk for future adverse cardiovascular events, and sets off a vicious cycle.