Physical activity on the job should be good
for a person's blood vessels--unless the job has a lot of stress,
which can cancel the activity's value, a study indicates.
"If you are performing the activity in a psychologically taxing
context, you are not going to see the benefit," said researcher
Cheryl Nordstrom. "The stress seems to negate it."
Another expert, however, considers that conclusion provocative
but not yet proved.
Nordstrom and her colleagues at the University of Southern
California's Keck School of Medicine looked at 447 utility workers
just after deregulation increased competition among utilities.
Results were presented March 2 at a meeting of the American Heart
Association in San Antonio.
The workers, ages 40-60, held jobs such as managers, meter
readers or administrative assistants. Nordstrom would not identify
the company or the type of utility, saying the researchers had
None of the workers was diagnosed at the start of the study as
having atherosclerosis, thickening of the arteries. Over three
years, the scientists used ultrasound imaging to measure any
thickening of the carotid arteries, which carry blood to the brain.
Thickening of these arteries in the neck can signal a buildup of
artery-clogging plaque deposits in other large vessels, including
ones in the heart.
Stress can raise clotting factors in the blood and may prompt
the release of fat into the bloodstream, which can lead to clogging
of the arteries. Physical activity, on the other hand, has been
shown to reduce levels of these fatty acids.
Researchers found, to their surprise, that people who got the
most physical activity on the job had the greatest thickening of
the arteries, Nordstrom said.
Conventional wisdom is that being active improves cardiovascular
health. And a separate part of the study supported the conventional
wisdom. This section found that the people who were most physically
active off the job--working up a sweat by exercising an average of
five times a week--had less progression toward atherosclerosis,
What could account for the difference between activity on the
job and activity off it? The scientists went back to a stress
questionnaire they had done earlier on the same people. The
questionnaire asked people about such things as whether there had
been a marked increase in their workload, and whether they had
trouble sleeping because their jobs were still on their minds.
The researchers found that the people who worked the hardest,
and who worked the most hours, reported the greatest job stress,
Nordstrom said. And when the researchers did statistical analysis,
it turned out that the job stress was most closely associated with
the increase in carotid thickening, she said.
"When I look at them together, the effect of the (physical)
activity drops out," Nordstrom said. "It becomes slightly
protective, which I would expect. But the stress indicators were
"These findings suggest that protective effects of physical
activity may be blocked or counteracted when activity is performed
in a psychologically stressful context," the researchers reported
in the abstract they presented at the conference.
Another expert, however, has his doubts. The USC conclusion that
job stress can lead to atherosclerosis is supported by some
previous studies but not by others, said Dr. Richard Stein, chief
of cardiology at Brooklyn Hospital Center in New York City and a
spokesman for the heart association. And the USC research also
leaves a lot of questions unanswered, he said.
For instance, the study did not ask the participants directly if
they felt anxious. "The guys might not have perceived stress,"
Stein said. "We are making an assumption."
The claim that job stress offsets the value of exercise is
"intriguing, but doesn't justify the conclusion," Stein said.
However, the report is worth following up, and "if this holds up
to that type of criticism, it is a very interesting observation,"