High levels of the stress hormone cortisol are closely linked to death from cardiovascular disease, a Dutch study suggests.
In a six-year study of 860 over-65s, those with the highest levels of cortisol had a five-fold risk of death from cardiovascular disease.
No link was found between high cortisol levels and other causes of death.
British experts said the Journal of Clinical Endocrinology and Metabolism study was "helpful".
Cortisol is produced in order to help the body recover from stress and regain its physiological stability.
But very high levels have been linked to risk factors for cardiovascualr disease, such as the metabolic syndrome - symptoms of which include obesity and high blood pressure - and accelerated atherosclerosis - where fatty deposits build up on the walls of the arteries.
In this study, researchers measured urinary cortisol levels in each participant. During the six years covered by the study, 183 people died. Cause of death was ascertained from death certificates.
The third of the subjects with the highest urinary cortisol had a five-fold increased risk of dying of cardiovascular disease.
'A lot to learn'
Nicole Vogelzangs of the University Medical Center, who led the study, said: "Previous studies have suggested that cortisol might increase the risk of cardiovascular mortality, but until now, no study had directly tested this hypothesis.
"The results of our study clearly show that cortisol levels in a general older population predict cardiovascular death, but not other causes of mortality."
"Our study shows that older persons with high levels of cortisol have an increased risk of dying from cardiovascular disease. This finding significantly adds evidence to the belief that cortisol can be damaging to the cardiovascular system."
Ellen Mason, senior cardiac nurse at the British Heart Foundation, said: "Stress is already associated with an increased risk of heart disease and this study throws up more evidence about the role of cortisol.
"However, there are other chemicals in our body besides cortisol which play a part when we're stressed out. So although this study helps, there is still a lot left to learn.
"It's important we all try and find ways to cope with stress which don't involve unhealthy habits that increase your risk of heart disease, such as smoking, drinking too much alcohol and eating foods high in saturated fat and salt."