Previous studies have found a higher incidence of heart disease among low-level workers, said Eric Brunner, an assistant professor of epidemiology at University College, London, and a member of the research team.

"This report is about mechanism," he said. "There is evidence now that socioeconomic status is related to heart rate and heart variability."

Metabolic Syndrome Link

The researchers had an ideal group to study -- 2,197 men in the British civil service, where all workers are meticulously graded by salary. Lower heart rate variability -- a lessened response to outside stimuli -- and faster heart rates were consistently found among the men with lower positions and less job control.

The heart rate of men in low-level positions averaged 3.2 more beats per minute than men in top-level positions, a statistically significant difference, the researchers reported.

The 20-year study also found that a higher heart rate and lower heart variability were closely associated with the incidence of metabolic syndrome, a combination of factors that increases the risk of heart disease.

That association persisted when the researchers accounted for factors such as smoking, poor diet and lack of exercise, the researchers reported in the June 7 issue of Circulation.

Consider Changing Jobs

The study suggests that the autonomic nervous system, which controls such subconscious functions as heartbeat, somehow responds to environmental factors, the researchers noted.

There is a lesson in the study for employers, Brunner said. "The ideal would be that the work situation would change, and there are signs of that," he said, at least in Great Britain, "where there is more attention being paid to making the workplace a more comfortable environment."

But the hard fact of working life is that senior executives have the most control over their conditions "and as you proceed down the work hierarchy, it becomes increasingly difficult to take control over problematical situations," he said.

And so the best advice for workers at the bottom of the ladder is that "someone who feels stressed out or unhappy about a job should take very good care of themselves and give consideration to changing jobs," Brunner said.

Women Weren't Included

Dr. Rita Redberg, a professor of medicine at the University of California, San Francisco, called the new study "very interesting," but said it wasn't conclusive because there were gaps in the research.

To start with, women weren't included in the study, she noted. And the researchers didn't report on "end points," such as an increase in heart attacks and other cardiac problems in the lower-level employees, she added.

"Heart rate variability is probably related to a lot of different things that have to do with fitness," she said. "You can't control for all of the other risk factors that might be responsible for the association they attribute to job status."

Redberg's conclusion: "It's a hypothesis-generating study, but we still need more data."

More information: The National Institute of Occupational Safety and Health has more on the hazards of job stress.