Regular, moderate-to-vigorous
aerobic exercise can reduce cellular changes
in the tissue lining the colon that can lead
to the formation of colon polyps and colon
cancer, a study suggests.
"This shows that you can see a biological effect
at the tissue level of exercise," Dr. Anne McTiernan
of the Fred Hutchinson Cancer Research Center
in Seattle stated. "This supports the observational
studies that people who exercise have a lower
risk of colon cancer."
However, the effects of exercise were only
seen among men in the current study. This
may have been because women just didn't exercise
as hard, McTiernan offers, or because their
workouts reduced their levels of estrogen,
which protects against colon cancer.
McTiernan and her team looked at the structure
of colonic crypts, microscopic pits in the
lining of the colon that help to absorb water
and nutrients. People with colon cancer show
increased cell growth within these crypts,
she explained. Specifically, the area of rapid
cell growth, or proliferation, extends higher
from the bottom of the crypt in patients'
tissue than in healthy individuals.
To investigate whether exercise might affect
these structures, the researchers randomly
assigned 202 healthy men and women aged 40
to 75 years to an exercise program with the
goal of working out moderately to vigorously
for one hour a day, six days a week, for a
year, or a control group who did not exercise.
All study participants had undergone a colonoscopy
within three years before the study, and then
had another colonoscopy after the study ended.
Men exercised for 370 minutes each week,
on average, compared to 295 minutes for the
women.
Men who exercised for 250 to 300 minutes
each week had a 1.7 percent reduction in the
extent of cellular proliferation within their
colonic crypts, while the men who exercised
more than 300 minutes weekly reduced it by
2.4 percent, the researchers found.
The men who exercised for less than 250 minutes
a week showed a 0.3 percent increase in the
height of cellular proliferation, while those
who didn't exercise had no change.
Among men who increased their cardiovascular
fitness by more than 5 percent, the reduction
in colon crypt cell proliferation height was
2 percent, compared to 0.9 percent for those
who exercised but showed lower gains in cardiovascular
fitness.
The findings support studies linking regular
aerobic exercise to lower colon cancer risk,
and suggest that exercise may cut this risk
by reducing cell proliferation in the colon,
the investigators conclude.
SOURCE: Cancer Epidemiology, Biomarkers &
Prevention, September 2006.
