For Some, Exercise May Increase Heart Risk
Fitness | By GINA KOLATA |
Michael Zamora/Corpus Christi Caller-Times, via Associated Press
Could
exercise actually be bad for some healthy people? A well-known group of
researchers, including one who helped write the scientific paper
justifying national guidelines that promote exercise for all, say the
answer may be a qualified yes.
By analyzing data from six rigorous
exercise studies involving 1,687 people, the group found that about 10
percent actually got worse on at least one of the measures related to
heart disease:blood pressure and levels of insulin, HDL
cholesterolortriglycerides. About 7 percent got worse on at least two
measures. And the researchers say they do not know why.
Marie ConstantinClaude Bouchard
“It is bizarre,” said Claude Bouchard, lead author of the paper, published on Wednesday in the journal PLoS One, and a professor of genetics and nutrition at the Pennington Biomedical Research Center, part of the Louisiana State University system.
Dr.
Michael Lauer, director of the Division of Cardiovascular Sciences at
the National Heart, Lung, and Blood Institute, the lead federal research
institute on heart disease and strokes, was among the experts not
involved in the provocative study who applauded it. “It is an
interesting and well-done study,” he said.
Others worried about its consequences.
“There
are a lot of people out there looking for any excuse not to exercise,”
said William Haskell, emeritus professor of medicine at the Stanford Prevention Research Center. “This might be an excuse for them to say, ‘Oh, I must be one of those 10 percent.’ ”
But
counterbalancing the 10 percent who got worse were about the same
proportion who had an exaggeratedly good response on at least one
measure. Others had responses ranging from little or no change up to big
changes, seen in about 10 percent, where risk factor measurements
improved anywhere from 20 percent to 50 percent.
“That should make
folks happy,” said Dr. William E. Kraus, a co-author of the study who
is a professor of medicine and director of clinical research at Duke. He
was a member of the committee providing the scientific overview for the
Department of Health and Human Services’ national exercise guidelines, which advise moderate exercise for at least 150 minutes a week.
The
problem with studies of exercise and health, researchers point out, is
that while they often measure things like blood pressure or insulin
levels, they do not follow people long enough to see if improvements
translate into fewer heart attacks or longer lives. Instead, researchers
infer that such changes lead to better outcomes — something that may or
may not be true.
Some critics have noted that there is no
indication that those who had what Dr. Bouchard is calling an adverse
response to exercise actually had more heart attacks or other bad health
outcomes. But Dr. Bouchard said if people wanted to use changes in risk
factors to infer that those who exercise are healthier, they could not
then turn around and say there is no evidence of harm when the risk
factor changes go in the wrong direction.
“You can’t have it both ways,” Dr. Bouchard said.
The
national guidelines for exercise are based on such inferences and also
on studies that compared the health of people who exercised with that of
people who did not, a weak form of evidence often said to be
hypothesis-generating rather than proof.
“We do not know whether
implementing exercise programs for unfit people assures better
outcomes,” said Dr. Lauer of the heart institute. “That has not been
established.” And so, he said, “there is a lot of debate over how strong
the guidelines should be in light of weak evidence.”
Authors of
the study say people should continue to exercise as before, but might
also consider getting their heart disease risk factors checked on a
regular basis. No intervention, including drugs, works for everyone, Dr.
Kraus said. So it should not be surprising that exercise does not work
for some.
“I am an exercise guy; I believe in exercise for
health,” Dr. Kraus said. “I would rather have everyone exercise. But you
can’t ignore the data.”
Still, he added, even if someone does not
get the expected benefit in some heart risk factors, there are other
reasons to exercise: for mental health and to improve physical
functioning.
And while the researchers would like to spare people
from adverse exercise effects, Dr. Bouchard said, “It is not possible
yet to make more specific recommendations because we do not understand
why this is happening.”
Dr. Bouchard stumbled upon the adverse
exercise effects when he looked at data from his own study that examined
genetics and responses to exercise. He noticed that about 8 percent
seemed to be getting worse on at least one measure of heart disease
risk. “I thought that was potentially explosive,” he said.
He then
looked for other clinical trials that also examined exercise under
controlled conditions, making sure that participants actually exercised
and did not change their diets, and carefully measuring heart risk
factors and how they changed with an exercise program. He found five
studies in addition to his own. In all the studies, a proportion of
people, about 10 percent, had at least one measurement of heart disease
risk that went in the wrong direction.
Then the researchers asked if there was some way of predicting who would have an adverse effect.
They
found it was not related to how fit the people were at the start of the
study, nor to how much their fitness improved with exercise. Age had
nothing to do with it, nor did race or gender. In some studies subjects
were allowed to take medications to control their blood pressure or
cholesterol levels. In others they were not.
Medication use did
not matter. The study subjects exercised at a range of intensities from
very moderate to fairly intense. But intensity of effort was not related
to the likelihood of an untoward effect. Nothing predicted who would
have an adverse response.
Some experts, like Dr. Benjamin Levine, a
cardiologist and professor of exercise sciences at the University of
Texas Southwestern Medical Center, asked whether the adverse responses
represented just random fluctuations in heart risk measures. Would the
same proportion of people who did not exercise also get worse over the
same periods of time? Or what about seasonal variations in things like
cholesterol? Maybe the adverse effects just reflected the time of year
when people entered the study.
But the investigators examined those hypotheses and found that they did not hold up.
Dr.
Kraus said researchers needed to figure out how to tailor exercise
prescriptions to individual needs. For example, people with good
cholesterol and insulin levels but worrisome blood pressure would want
to know if exercise made their blood pressure rise. A rise in blood
pressure would not be compensated by improvements in already good
cholesterol or insulin levels.
Dr. Lauer said that if nothing
else, the study pointed out the need to know more about what exercise
actually does. “If we are going to think of exercise as a therapeutic
intervention, like all interventions there will be adverse effects,” he
said.
He said, “There is a price for everything.”