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By IRA DREYFUSS : Associated Press Writer
Jun 16, 2003 : 3:43 pm ET
WASHINGTON -- New research labels as an
"illusion" a major study's conclusion that couch potatoes who take
up at least moderate regular exercise can reduce their risk of dying
early.
The apparent benefit "can be entirely
attributed to measurement error," said researcher Paul T. Williams,
a biostatistician in the Life Sciences Division of Lawrence Berkeley
National Laboratory in Berkeley, Calif.
However, the lead scientist in the original
study says additional data from the research project can prove him
right. And other experts say that even if Williams' analysis is
correct, other studies have shown so many health benefits from
exercise that it must extend lifespan.
Williams examined a landmark study published
in 1995 in the Journal of the American Medical Association by
scientists at the Cooper Institute, a Dallas-based organization that
studies exercise and lifestyle. However, his conclusions could be
applied to other studies that used the research format employed by
the Cooper Institute project, Williams said.
The Cooper Institute team looked at data on
9,777 men who had taken two treadmill exercise tests almost five
years apart. The scientists then followed the men for more than five
years. The researchers adjusted statistically for age and other risk
factors, so they could focus on seeing if exercise affected the risk
of death.
Men in the least-fit 20 percent on both
treadmill tests were most likely to die, the study found. However,
men whose times had improved enough on the second test to pull
themselves out of the least-fit group had a lower risk of death, the
study found.
Men who were unfit on the first test and fit
on the second had a 44 percent reduction in their risk of death,
compared with men who were unfit on both tests, the study found.
The researchers concluded that getting out of
the least-fit group could pull people out of the group at highest
risk of early death. The finding is commonly cited to support
current federal guidelines on physical activity, which call for
doing at least 30 minutes of moderate activity on most, if not all,
days of the week.
But Williams contends the researchers did not
account sufficiently for the fact that the treadmill test is not a
perfect measurement of physical ability. The test has a good day-bad
day problem: A person might go longer in one test and shorter in
another while having the same underlying fitness, he said.
In his experiment, Williams ran numbers on a
computer model. He created two hypothetical treadmill tests, and
varied the scores according to his assumptions of measurement error.
His results were the same as the Cooper
scientists described in the JAMA article, Williams said.
And if the article's results can be explained
by measurement error, scientists must reject the conclusion that
there were improvements due to physical activity, Williams said. "It
hasn't been proved that changing to moderate exercise would affect
your life expectancy," he said.
Williams believes physical activity can
improve health, but that moderate activity such as brisk walks are
not enough to reap a big benefit. "Real health benefits are achieved
with more vigorous exercise," he said. "If you are unfit and you
become substantially fit, I believe that will change your life
expectancy."
Williams' challenge is itself challenged by
Steven N. Blair, president and CEO of the Cooper Institute, who led
the JAMA article study team as a scientist, before his promotion.
Men whose fitness improved on the treadmill
tests also reported a corresponding change in their physical
activity, Blair said. Those self-reports are a sign that the
improved lifespans were the result of improved living, not a glitch
in the methodology, he said.
A colleague of Blair, digging deeper into the
Cooper Institute data, said he was seeing physical changes which
also argue that the lifespan improvements are real.
"The idea that people don't change on
repeated measures is absolute nonsense. They do, and we've got the
data to prove it," said Tony Jackson, a professor of health and
human performance at the University of Houston.
"People who actually changed their treadmill
times altered their body composition in desirable ways," Jackson
said.
At Stanford University, medical professor and
physical activity researcher William Haskell felt Williams made a
point in criticizing the design of the Cooper study. "It does raise
an issue about how much weight we should be putting on those
studies," he said.
Haskell, who also is a member of the Cooper
Institute's board of scientific advisers, does not consider the case
closed. He's waiting for Blair's response.
Another institute board member, I-Min Lee of
the Harvard School of Public Health, noted that some measurement
error is a normal part of science. But, she said, other studies give
lots of reasons to think that moderate exercise should improve
health enough to reduce the risk of an early death.
"If (Blair's) study were the only one, I
probably wouldn't put as much weight on it, but it is a piece of the
puzzle that fits into the larger picture," Lee said.
Other studies have shown that exercise
reduces such health risks as body fat, cholesterol levels and
insulin sensitivity, and those improvements are markers of long-term
good health, Lee said.
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