LONDON (Reuters) - Work really can kill you, according to a study on Wednesday providing the strongest evidence yet of how on-the-job stress raises the risk of heart disease by disrupting the body's internal systems.
The findings from a long-running study involving more than 10,000 British civil servants also suggest stress-induced biological changes may play a more direct role than previously thought, said Tarani Chandola, an epidemiologist at University College London.
"This is the first large-scale population study looking at the effects of stress measured from everyday working life on heart disease," said Chandola, who led the study. "One of the problems is people have been skeptical whether work stress really affects a person biologically."
Heart disease is the world's leading cause of death. It is caused by fatty deposits that harden and block arteries, high blood pressure which damages blood vessels, and other factors.
The researchers measured stress among the civil servants by asking questions about their job demands such as how much control they had at work, how often they took breaks, and how pressed for time they were during the day.
The team conducted seven surveys over a 12-year period and found chronically stressed workers -- people determined to be under severe pressure in the first two of the surveys -- had a 68 percent higher risk of developing heart disease.
The link was strongest among people under 50, Chandola said.
"This study adds to the evidence that the work stress-coronary heart disease association is causal in nature," the researchers wrote in the European Heart Journal.
Behavior and biological changes likely explain why stress at work causes heart disease, Chandola said. For one, stressed workers eat unhealthy food, smoke, drink and skip exercise -- all behaviors linked to heart disease.
In the study, stressed workers also had lowered heart rate variability -- a sign of a poorly-functioning weak heart -- and higher-than-normal levels of cortisol, a "stress" hormone that provides a burst of energy for a fight-or-flight response.
Too much cortisol circulating in the blood stream can damage blood vessels and the heart, Chandola said.
"If you are constantly stressed out these biological stress systems become abnormal," Chandola said.
Reporting by Michael Kahn; Editing by Maggie Fox and Caroline Drees