FRIDAY, Feb. 7, 2014 (HealthDay News) -- Exercise has long been
credited with both reducing the risk of breast cancer and surviving
Now a new study suggests, but doesn't prove, that breast cancer
survivors who run have an even greater survival edge than those who
"Exercise per se lowers the risk of breast cancer death, but, more importantly, we found a difference between walkers and runners," said study author Paul Williams, a staff scientist at the Lawrence Berkeley National Laboratory in Berkeley, Calif.
"We see these huge reductions [in breast cancer deaths] in women who run -- much greater than those who walk," Williams said. "[Even so], we don't see this as negating the benefit of walking."
But running appears to confer more protection than walking in
reducing the risk of dying from breast cancer, he said.
The study was published online recently in the
International Journal of Cancer.
Williams compared two groups from his long-running National
Runners' and Walker's Health Study. He followed nearly 300 runners
and more than 700 walkers, all of whom had been diagnosed with
breast cancer. During the nine-year study, 33 of the walkers and 13
of the runners died from breast cancer.
Williams took into account other factors that might influence
survival, such as age, family history, race and menopausal
When he looked at all the women as a single group, he found
about a 25 percent reduction in death from breast cancer during the
follow-up period for every mile of brisk walking or two-thirds of a
mile of running.
When he looked at just the runners, however, he found that the
same amount of running reduced the risk of death by more than 40
percent. The runners who averaged more than two and a quarter miles
per day had a 95 percent lower risk of death from breast cancer
during the follow-up period.
The walkers' risk of breast cancer death for every mile walked
each day declined just 5 percent, which wasn't statistically
significant, Williams said.
Williams said he can't explain the link between more vigorous
exercise and a lower death risk. And he found only an association
between the two, not a cause-and-effect link.
"Running may be more effective in interrupting the hormone cycle and lowering estrogen in a woman's system," he said, and the lower estrogen levels mean less fuel for breast cancer to grow.
But some breast cancer experts have reservations about the study
findings, including Leslie Bernstein, director of cancer etiology
at the City of Hope Comprehensive Cancer Institute, in Duarte,
Although the message to exercise is a good one, the data used
for the study lacks some vital information, Bernstein said.
Williams acknowledged the lack of certain data, such as the
self-reporting of the participants, how advanced the cancer was at
diagnosis, what type of breast cancer it was and what treatment was
Other factors might have influenced the findings, too, Bernstein
said. For instance, the runners might have had less advanced
disease than the walkers. She said she is not aware of any other
studies showing such a dramatic difference in survival between
runners and walkers, and she has published extensive research on
exercise and breast cancer.
Her advice to breast cancer survivors? "I would say it's better
to run than to walk because you spend more energy," Bernstein said.
"But you can only do what's good for you. Older women will probably
not want to run unless they have been running all along."
The plan to run after breast cancer treatment might be better
for younger women, she said. Experts advise checking with a doctor
before starting a workout regimen.
Those who decide to walk can think about doing so more briskly,
with a doctor's approval. "If you walk, push yourself so you're out
of breath," Bernstein said.
To learn more about breast cancer, visit the
American Cancer Society.
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