For
people diagnosed with cancer, the risk of cancer death falls as physical
activity rises, according to a new analysis of more than 70 existing studies.
Researchers found the same holds true for everyone - supporting the current
World Health Organization recommendation of moderate physical activity to
combat the risk of chronic disease, they write in the British Journal of Sports
Medicine.
The
WHO recommends two and a half hours of moderate exercise per week for some
health benefit and five hours of moderate exercise per week for additional
benefit. Half as much time per week of vigorous physical activity, like
running, may confer the same benefits.
There are no specific recommendations for physical activity levels to combat
cancer risk, although more activity has been tied to lower risk of death from
breast, colorectal and prostate cancers, the authors note.
"Our
results might help to update the recommendation concerning the advisable amount
of physical activity to reduce cancer mortality," said senior author Dr.
Li Liu of Huazhong University of Science and Technology in China.
Doctors
could start to incorporate physical activity into cancer treatments, Liu told
Reuters Health by email.
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The
researchers included 71 studies of physical activity and cancer death risk in
the general population or among cancer survivors.
When
they pooled these results, people in the general population who got at least
two and half hours of moderate activity like brisk walking, per week, were 13
percent less likely to die from cancer than those with the lowest activity
levels.
They also looked at data in terms of MET-hours, a measure of the relative
amounts of energy expended in given activities and time spent doing them.
Resting represents 1 MET, while a 4-MET activity like brisk walking uses four
times as much energy, according to the U.S. Office of Disease Prevention and
Health Promotion. Doing a 4-MET activity for 30 minutes equals 2 MET-hours.
Cancer
survivors who completed at least 15 MET hours per week of physical activity
were 27 percent less likely to die from cancer.
Exercise after cancer diagnosis reduced cancer death risk more than
prediagnosis exercise, the study team notes.
Exercise may change the body's response to cancer, and those who exercise more
may live healthier lifestyles in other ways as well, Liu said.
But many of the high-quality studies included in this analysis accounted for
other healthy-lifestyle factors that may have played a role, Liu noted.
"Physical
activity, mostly before diagnosis, and breast cancer mortality has been studied
for decades, but only in the last 10 years or so have we been studying physical
activity after diagnosis," said Patrick T. Bradshaw of the University of
California, Berkeley, who was not part of the new study.
"Other
cancers (e.g. colorectal, ovarian) have been studied much less than breast
cancer, but some researchers there have also found a reduction in mortality
associated with increasing physical activity levels," Bradshaw told
Reuters Health by email.
So
far, most studies have not been able to address which types of physical
activity are most beneficial, he said.
Leisure time physical activity or recreational physical activity, but not
occupational activity, is protective against cancer according to most research,
Liu said.
"The
take-home message here is encouraging - exercise may be beneficial even if
started after diagnosis," Bradshaw said.
"Based
on huge evidence of the inverse association between physical activity and
cancer mortality, there is no doubt that cancer patients should be physically
active," Liu said. "We suggest that cancer patients to consult their
doctors about a personalized physical activity plan, including exercise time,
exercise frequency, exercise mode and so on, which may help to promote the
survival of patients without bringing too much physical burden."