Physical activity, body
mass index, and energy intake Evidence from epidemiological studies is
strong that men with high occupational or recreational physical activity
seem to have a decreased risk of colon cancer. Such evidence comes from
follow up studies of cohorts who are physically active or who
physically demanding jobs,
as well as from case-control studies that have assessed physical activity
by, for example, measurement of resting heart rate or questionnaire. The
association remains even after potential confounding factors, such as diet
and body mass index, are controlled for.
The available data,
however, show no consistent association between obesity and risk of colorectal
cancer (analysis and interpretation of this factor is difficult in retrospective
studies, where weight loss may be a sign of the disease), although evidence
now suggests an association between obesity and adenomas. This increased
risk associated with energy intake Box 1.1 Physical activity and
colorectal cancer
Hormone replacement therapy
evidence supports an (originally
unexpected) association between hormone replacement therapy and a reduced
risk of colorectal cancer.
Of 19 published studies
of hormonal replacement therapy and risk of colorectal cancer, 10 support
an inverse association and a further five show a significant reduction
in risk. The risk seems lowest among long term users. Although some contradictions
still exist in the available literature, hormone replacement therapy seems
likely to reduce the risk of colorectal cancer in women. The risk seems
to halve with 5-10 years' use. The role of unopposed versus combination
hormone replacement therapy needs further research. Box 1.2 How individuals
can reduce their risk of colorectal cancer.
This question is important;
if the link is indeed causal, women who are at high risk of colorectal
cancer could be offered the therapy to lower their risk.
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