May 16, 2016 / 12:27 PM
CDT / Updated May 16, 2016 / 12:29 PM CDT
By Maggie Fox
A large
new study confirms that exercise lowers the risk of many different types of
cancer, and it goes a step further: It shows just how much the reduction in
risk is.
People
who exercised the most had a 42 percent lower risk of esophageal cancer and a
27 percent lower risk of liver cancer over 11 years than people who exercised
the least, the study of 1.4 million people showed.
Those
who exercised the most had:
·
A 26 percent lower risk of lung cancer
·
A 23 percent lower risk of kidney cancer
·
A 22 percent lower risk of stomach cancer
·
A 21 percent lower risk of endometrial cancer
·
A 20 percent lower risk of myeloid leukemia
·
A 17 percent lower risk of myeloma
·
A 16 percent lower risk of colon cancer
·
A 15 percent lower risk of head and neck cancer
·
A 13 percent lower risk of rectal cancer
·
A 13 percent lower risk of bladder cancer
·
A 10 percent lower risk of breast cancer
The
team at the National Cancer Institute looked at dozens of cancer studies in the
U.S. and Europe, and threw all their findings together into a single analysis.
They compared the people who exercised more than 90 percent of everyone else in
the study to those who exercised the very least.
Mark
Holloway of Clemmons, N.C., goes through part of his exercise routine at the
Jerry Long YMCA in Clemmons, Tuesday, March 1, 2016.Skip Foreman / AP
The
biggest exercisers got in the equivalent of just over an hour a day of brisk
walking, said Steven Moore of the National Cancer Institute, who led the study.
They
included studies that just looked at strenuous exercise, such as running, and
at studies that looked at more moderate exercise, including swimming and
strolling and even vigorous yardwork.
On
average, the exercisers did two and a half hours of moderate exercise, such as
walking, every week. This is about the average for the U.S. as a whole.
“A
higher level of leisure-time physical activity was associated with a 7 percent
lower risk of total cancer,” they wrote in their report, published in the
Journal of the American Medical Association’s JAMA Internal Medicine.
Exercise
has all sorts of benefits, Moore said. "it can help people reduce their
risk of heart disease. It can reduce the risk of diabetes. It extends life
expectancy. And now it appears that it may reduce the risks of some
cancers," Moore told NBC News.
“This
finding may help encourage those who are overweight or obese to be physically
active."
“Furthermore,
our results support that these associations are broadly generalizable to
different populations, including people who are overweight or obese, or those
with a history of smoking.”
Obesity
is a well-known risk factor for cancer, but exercise protected even obese
people from cancer, the study found. On average, the people in the study were
slightly overweight.
“This finding may help encourage those who are
overweight or obese to be physically active,” Moore’s team wrote.
While
it's always possible that people who are able to exercise more are healthier in
other ways and less likely to develop cancer for some other reason, cancer
experts say the evidence is very convincing that exercise directly affects the
growth of tumors.
There
are three possible ways exercise might lower cancer risk, Moore said. It can lower
levels of hormones such as estrogen, which in turn lowers breast and
endometrial cancer risk, he said. It helps the body better regulate insulin,
and it may lower inflammation.
One odd
finding: exercise lowered the risk for lung cancer, but only among current and
former smokers.
Exercisers
did have a higher risk of melanoma, probably because they often exercised
outside. The researchers stress that if you exercise outdoors, you need to use
sunscreen.
And men
who exercised had a higher rate of prostate cancer. “There is no known biologic
rationale to explain this association,” the researchers wrote.
It’s
possible, they said, that men who are physically active also are more likely to
go to the doctor and get screening tests for prostate cancer, which in turn
show up prostate tumors that are slow-growing and not necessarily dangerous to
the man.
Doctors
should be prescribing exercise to their patients, Moore's team said. Only about
half of Americans get the minimum recommended amount of exercise.
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