Insight into the anti-cancer effect of exercise

By Martha Kerr

NEW YORK (Reuters Health) – The anti-cancer effects of
exercise are due to increases in a protein that blocks cell
growth and induces cell death, according to Australian
researchers.

The protein, called insulin-like binding protein-3
(IGFBP-3), inhibits another protein called insulin-like growth
factor-1 (IGF-1), thereby blocking IGF-1′s proliferative effect
on cell growth, the study hints.

Dr. Andrew M. M. Haydon and colleagues at Manash Medical
School in Melbourne identified new cases of colorectal cancer
in the Melbourne Collaborative Cohort Study, a prospective
study of 41,528 adults recruited between 1990 and 1994.

The investigators looked at baseline body mass index and
level of physical activity reported and compared baseline
levels of IGF-1or IGFBP-3 with those measurements.

Analyses centered on 443 colon cancer patients followed for
more than 5 years.

Among subjects who were physically active, an increase in
IGFBP-3 was associated with a 48 percent reduction in colon
cancer-specific deaths. No association was apparent for IGF-1.

For the physically inactive, there was no association
between IGF-1 or IGFBP-3 and colon cancer survival.

Haydon told Reuters Health that that “physical activity can
increase IGFBP-3 levels, which, in turn, reduces the amount of
free IGF-1.” IGF-1 has been shown to stimulate cell growth,
inhibit cell death, and promote angiogenesis — the formation
of new blood vessels, which tumors need to grow.

“We did not look at the amount of physical activity needed
to reduce colorectal cancer incidence, as we only looked at
those from our cohort who had CRC,” Haydon pointed out.

“Other studies that have looked at this have shown a
dose-effect, meaning the more exercise the lower the risk,
however our study did not try to address this issue. We were
examining the effect of physical activity on one’s prognosis
following a diagnosis of bowel cancer and the possible
mechanisms behind this effect.”

SOURCE: Gut, May 2006.