Exercise and
Cancer
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:
|
cardiovascular capacity |
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:
- Insulin
-
Prostaglandins
- Bile acid
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
Concerning these strongly
hormone-dependent cancers the editorial states:
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).
Prostate Cancer
The editorial notes that 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
The editorial notes that:
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
The editorial notes that, 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
Conclusion
The editorial notes that 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."
British Medical Journal
December 9, 2000;321:1424-1425
