More Evidence That
Exercise Prevents Cancer
A growing body of evidence continues to support previous research
about the cancer-fighting benefits of exercise and link between
physical activity and cancer prevention. Experts are now creating
guidelines on diet and exercise, which for the first time puts
exercise on an equal footing with nutrition.
"We now believe physical activity is a primary component
of preventing cancer," says Abby Bloch, chairwoman of the
American Cancer Society's advisory committee on nutrition and
physical activity.
Until recently, definitive scientific proof has been elusive.
While most of the clear benefits of exercise, such as weight loss,
can be seen relatively quickly, its impact on - cancer can take
years. And the relationship has never been as clear-cut as that
between smoking and lung cancer, for example, or sun exposure
and skin cancer.
In recent years, however, scientists have begun to connect the
dots between regular sustained workouts and the prevention of
several types of cancers, among them intestinal, endometrial,
colon, breast and lung.
A survey based
on information collected over a 23-year period in a research project
called the Copenhagen Male Study found that regular
exercise can help prevent intestinal cancer. The study comprised
5,000 men divided into four separate groups ranging from those
who exercise very little to those who exercise a lot. Doctors
examining the material believe that moderate physical activity
strengthens the immune system and therefore helps prevent the
cancer from developing.
"My study shows that just by walking or cycling regularly,
by taking what one calls regular physical exercise, can prevent
this very serious and very common form of cancer. Several other
studies have had similar results, and one can now say that any
doubt has been dispelled." Said Doctor Inge Haunstrup Clemmensen
from the Cancer Foundation to the daily newspaper Politiken. The
doctor also stated that the study results indicate that moderate
physical activity also reduces the risk of cancer of the oesophagus.
"Another
closely related theory is that we know that increased activity
increases intestinal function. As a result the harmful contents
that could constitute a cancer risk are present in the organism
for a much shorter period of time and therefore lessen the risk."
Said Clemmensen to Politiken.
A recent study revealed that physical activity prevents endometrial
cancer and breast cancer according to a study involving 850
women. The more the study subjects exercised, the less their
odds of being diagnosed with cancer, even if they were considered
"at risk" for the disease.
The science
has gotten to the point where it has attracted a lot of attention,
and I predict the next decade (of research in this area) will
be a very exciting time, " says Steven N. Blair, an epidemiologist
with the Cooper Institute for Aerobics Research in Dallas' Texas,
who is studying the relationship between lung cancer and exercise.
Blair is studying the effects of exercise on lung cancer, and
his preliminary results suggest that higher fitness levels are
associated with a lower risk of developing the disease. In his
study, unfit men were about twice as likely to die of lung cancer
than fit men, he says.
His research found that moderately fit men had a 20 percent
lower risk of dying of lung cancer compared with men who were
not fit. And men who were highly fit had a 60 percent lower
risk than men who were not fit, he said. This appeared true
even after adjusting for smoking habits.
"Fitness protects, whether you are a smoker or not,"
he says, although he is not exactly sure why. He doubts the
reason is that exercise improves lung function. Rather, it is
more likely that exercise strengthens the body's immune system,
believed to play a significant role in staving off the onset,
or worsening, of many types of cancer.
Experts believe that one-third of the annual cancer deaths can
be attributed to diet and sedentary habits, with another third
due to cigarette smoking; thus, lifestyle choices have become
increasingly important. To be sure, genetic inheritance influences
cancer risk, too, but most of the variation in cancer risk across
populations and among individuals is due to non-inherited factors.
Those who regularly exercise tend to practice other healthful
habits. They are less likely to consume saturated fats - especially
animal fat - and are more likely to eat increased fiber and
to shun cigarettes. They also are leaner than average, which
helps, because obesity is a risk factor for many cancers.
The most
compelling evidence thus far tying exercise to cancer prevention
involves cancers of the colon and breast, although scientists,
suspect that exercise also might play a role in lowering the
chances of prostate, lung, non Hodgkin's lymphoma, ovarian,
testicular and uterine cancers. Unquestionably "there are
lower cancer death rates in both men and women" who are
physically fit, says Blair, who is the Cooper Institute's director
of research. "Active and fit people have less of a chance
of dying of cancer."
Colon cancer, one of the nation's leading cancer killers, is
the one cancer where the impact of exercise appears indisputable.
Numerous studies have shown that exercisers have a substantially
lower risk - some studies have shown it to be as much as 50
percent - of developing colon cancer than couch potatoes.
"The epidemiologic evidence for a preventive role for physical
activity is strong and consistent for colon cancer," says
Aaron Blair, brother of Steven Blair and chief of the occupational
epidemiology branch of the National Cancer Institute, part of
the National Institutes of Health.
Most experts theorize that the reason for this is that exercise
accelerates the movement of material through the colon, and
cancer causing substances dont have time to linger - and make
trouble - because they leave the body quickly
The fact
that exercise is now being shown to prevent cancer is important
for one more reason: it proves that cancer is systemic, not
local. In other words, cancer is a whole-body failure, not just
a specific tumor or lesion that can be surgically removed or
targeted with radiation. Because cancer is a systemic failure,
it must be treated holistically -- that is, the whole person
must be considered: their physical health, immune system function,
mental health, spiritual health, and of course their day to
day activities such as eating and exercising.
Physical
Activity and Specific Cancers
Recently, an editorial in the British Medical Journal explored
the relationship physical activity and cancer. Epidemiologists
David Batty from London and Inger Thune from Norway reviewed
some of the evidence regarding the wide range of potential cancer-protective
effects of exercise. Below are some excerpts and important points
from the editorial.
To start,
they note that exercise has significant effects on several functions
of the human body that may influence cancer risk. These effects
include changes in the following:
-
- energy
balance
- pulmonary
capacity
- immune
function
- bowel
motility
- antioxidant
defence
- hormone
levels
- DNA
repair
They note
that in the past decade alone, over 200 population based
studies have linked physical activities to cancer risk.
The most researched cancers are those of the:
- Bowel
- Breast
- Endometrium
- Prostate
- Testes
- Lung
Bowel Cancer
Cancer of
the large bowel is the most commonly investigated cancer in
relation to physical activity (1-4) with physically active men
and women experiencing around half the risk of their sedentary
counterparts.
Plausible
mechanisms of protection include the beneficial effects of exercise
on levels of the following substances, which influence the growth
and proliferation of cells in the colon:
In addition,
exercise reduces bowel transit time and thereby the duration
of contact between fecal carcinogens and the mucosal lining
of the colon.
Breast
and Endometrial Cancer
Endogenous
sex hormones are strongly implicated in the development of
breast and endometrial cancer. Physical activity may modulate
the production, metabolism, and excretion of these hormones,
so an association with these cancers is biologically possible.
Physical
activity may also reduce the risk of cancer through its normalising
effect on body weight and composition. Evidence from population
based studies suggests that occupational, leisure, and household
activities are associated with about a 30% reduction in breast
cancer rates (5)… Those studies that have explored the
link between physical exertion and the risk of endometrial
cancer suggest a negative association (1,3).
In September, the American College of Sports Medicine released
a Canadian study published in its journal, Medicine &
Science in Sports & Exercise, that looked at 1,233 cases
of breast cancer and 1,237 "controls" (women who
did not have the disease), comparing their lifetime physical
activity patterns and other factors, including diet, tobacco
and alcohol use and family history.
The study found that the greatest risk reduction for breast
cancer occurred among those women who engaged regularly in
"moderate intensity" job or household activities,
such as farming or household chores.
Such activities appear to be more beneficial than recreational
pursuits of any intensity that were performed inconsistently,
whether it be an occasional brisk walk or game of tennis.
Earlier research released two years ago from the landmark
Nurses Health Study at Brigham and Women's Hospital in Boston
showed that women who exercise an hour a day or more might
reduce their risk of breast cancer by 20 percent. Those who
work out two to four hours a week experienced a 10 percent
reduction in risk.
The study was based on analysis of questionnaires from 121,701
women. Researchers examined 20 years of health and activity
data from women ages 30 to 55, from 1976 to 1996.
A smaller 1997 study in Norway found that women who exercised
at least four hours a week were about a third less likely
to get breast cancer.
Beverly Rockhill, the lead researcher in the Boston study
and an epidemiologist at the University of North Carolina
at Chapel Hill, says the connection between exercise and breast
cancer might be due, to the fact that ' exercise reduces the
level of circulating estrogens in a woman's body. Estrogen
stimulates the growth of breast cells, which might-encourage
cancer.
"A woman is exposed to circulating hormones her whole
life. To prevent breast canceL she has to reduce them over
a long period of time," Rockhill says. "What seems
to be important is sustained activity. Women need to pick
up an activity they can stick with."
In this study, the nurses who demonstrated a lower cancer
risk walked briskly, ran, jogged and performed aerobics and
calisthenics, Rockhill says. Unlike in the later Canadian
study, "we did not count such things as easy walking,
gardening or housework," she says.
But Rockhill warns that women shouldn't necessarily overdo
it. "They have to tread a fine line between too much
and too little exercise, because too little estrogen can increase
the risk of heart disease and osteoporosis," she says.
Postmenopausal women taking hormone replacement and who exercised
enjoyed the same protective benefits, Rockhill says. One possible
explanation is that the production of natural estrogen was
probably reduced; after menopause, estrogen is produced in
the fat cells, rather than in the ovaries. Women who exercise
are typically leaner and would produce less natural estrogen
as a result.
Prostate Cancer
Since athletes
show lower levels of circulating testosterone than non-athletes,
and testosterone influences the development of prostate cancer,
this has led to the hypothesis that physical activity may protect
against this cancer. Most, but not all, studies suggest a protective
effect (3).
Lung Cancer
Although
physical activity improves pulmonary ventilation and perfusion,
which may reduce both the concentration of carcinogenic agents
in the airways and the duration of agent-airway interaction,
the association of activity with lung cancer has received relatively
little attention. Findings from most, but not all, studies suggest
a negative relation…(1,3)
Exercise as a Cancer Treatment
In addition
to the apparent role of exercise in the prevention of some cancers,
there is growing interest in and evidence of its use in the
treatment and rehabilitation of patients with cancer (12, 13).
Physical activity may reduce the likelihood of recurrence and
enhance survival through its capacity for doing the following:
- Improving
bodily movement
- Reducing
fatigue
- Enhancing
immune function
Since exercise seems to have protective effects against some
types of cancers and does not increase the risk of any cancer,
it should be more actively encouraged. They state that "in
light of the decreasing population prevalence of total physical
activity, doctors should advocate moderate endurance-type activity,
such as walking and cycling. As well as reducing the risk of
chronic diseases such as coronary heart disease and non-insulin
dependent diabetes, such physical activity
does seem to protect against some cancers."
References:
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3. McTiernan A, Ulrich C, Slate S, Potter J. Physical activity
and cancer etiology: associations and mechanisms. Cancer Causes
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Berry TD. Energy balance and colon cancer beyond physical activity.
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issues related to the association between physical activity
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11. Thune I, Lund E. The influence of physical activity on lung-cancer
risk: A prospective study of 81,516 men and women. Int J Cancer
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12. Courneya KS, Mackey JR, Jones LW. Coping with cancer. The
Physician and Sports Medicine 2000; 28: 49-73
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J. Effects of physical activity on the fatigue and psychologic
status of cancer patients during chemotherapy. Cancer 1999;
85: 2273-2277.
14. Davey Smith G, Shipley MJ, Batty D, Morris JN, Marmot M.
Physical activity and cause-specific mortality in the Whitehall
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15. Marlene Cimons, Experts give more weight to exercise in
preventing cancer, Los Angeles Times Syndicate
16. Mike Adams, Physical exercise prevents cancer, News Target
Alerts; May 19, 2004
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