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On-the-Job Exercise Not Always Heart-Healthy

Study finds stress levels may reduce benefits

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FRIDAY, Aug. 8, 2003 (HealthDayNews) -- For years, fitness gurus have extolled the virtues of exercise as a way to reduce the risk of heart disease.

But if you get that exercise on the job, it's not necessarily improving your heart health, claims a new study.

In fact, the study says, physically demanding jobs may cause faster progression of atherosclerosis, or hardening of the arteries.

The culprit, however, appears to be not the activity itself, but the stress that often accompanies physically demanding jobs, says the study, which appears in the July issue of the American Journal of Medicine.

"It's not the activity itself at work, but rather what tends to go along with it," says study leader James Dwyer.

"The modern structure of the work force is that jobs that involve more physical activity tend to involve more stress," adds Dwyer, a professor of preventive medicine at the University of Southern California's Keck School of Medicine. "Those who are left doing physically demanding work tend to be in jobs that involve insecurity and stresses."

Dwyer and his colleagues followed 500 healthy, 40- to 60-year-old employees of a utility company for three years each, for a total of six years. The study gauged stress through questions such as how much sleep employees lost because of concerns about work or whether they lacked time to go to lunch.

Researchers measured the progression of atherosclerosis using high-resolution ultrasound to look at the thickness of the arteries in the neck at 18-month intervals. Both work and leisure-time exercise were monitored.

By looking at both the stress and physical activity, Dwyer says, researchers resolved an apparent contradiction: How could exercise be harmful to cardiovascular health?

"Those people who were high on that psychological stress scale showed more rapid progression of the underlying disease," Dwyer says. "And that relationship explained the apparent adverse effect of physical activity at work."

But he adds that not all physically active jobs would necessarily be stressful. Aerobics instructors, for example, might enjoy their work and derive the same health benefits of exercise as their students, Dwyer says.

The study also confirms the benefits of leisure-time exercise. Compared with those who exercised vigorously at least three times a week, atherosclerosis progressed twice as fast in moderate exercisers such as regular walkers and three times as fast in couch potatoes, the study says.

The researchers say their study, supported by the National Institutes of Health, differs from other recent research on workplace and leisure-time activity because it measured the progression of atherosclerosis during its development while monitoring exercise at the same time. Some other studies, the researchers say, relied on subjects' memories of past activity, after heart attacks had occurred.

Dr. Richard A. Stein, an associate chairman of medicine at Beth Israel Medical Center's Singer Division in New York City, says research findings on possible relationships between stress and coronary disease vary widely.

The latest study raises an "interesting question" about job stress and coronary disease, says Stein, a professor of clinical medicine at the Weill Cornell Medical Center in New York City and a spokesman for the American Heart Association.

Some studies, he says, have concluded that workplace stress increased the risk of coronary disease. But a study on air traffic controllers showed no increase in heart attack risk. "And that certainly is as stressful a job as I can imagine," Stein says.

In addition, he says, the physiological reaction to stress has a lot to do with how you respond to the source of stress. For example, one person might be stressed by arriving to find a pile of papers on the desk, while another might not.

Among those in the study, Stein says, "exercise relating to the job did not seem to be protective" against atherosclerosis. That could be explained in part by links between high stress levels and work-related exercise, he says, but further study would be needed to determine whether that's the case.

More information

For more on atherosclerosis, check with the American Heart Association. Test your knowledge of exercise and its effects on heart health by taking this online quiz by the National Heart, Lung, and Blood Institute.

SOURCES: James Dwyer, Ph.D., professor, preventive medicine, Keck School of Medicine, University of Southern California, Los Angeles; Richard A. Stein, M.D., associate chairman, medicine, Beth Israel Medical Center, and professor, clinical medicine, Weill Cornell Medical Center, New York City; July 2003 American Journal of Medicine
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