According to Australian researchers exercise appears to slow down the growth of cancer cells because it increases a protein that blocks cell growth and induces cell death.
The study suggests the anti-cancer 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 proliferate effect on cell growth.
Dr. Andrew M. M. Haydon and colleagues at Monash Medical School in Melbourne used a prospective study of 41,528 adults recruited between 1990 and 1994, the Melbourne Collaborative Cohort Study, to identify new cases of colorectal cancer.
They looked at baseline body mass index and levels of physical activity reported and compared baseline levels of IGF-1or IGFBP-3 with those measurements.
Their analysis focused on 443 colon cancer patients who had been monitored for more than 5 years.
In patients who were physically active, an increase in IGFBP-3 was associated with a 48 percent reduction in colon cancer-specific deaths.
No association was observed for IGF-1.
For the physically inactive, there was no association between IGF-1 or IGFBP-3 and colon cancer survival.
Haydon says 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.
But the team, led by Dr Andrew Haydon from Monash Medical School in Melbourne, cannot say how much exercise someone needs to show these effects as the team just examined the effect of physical activity on a prognosis following a diagnosis of bowel cancer.
The researchers publish their results in the May issue of the journal Gut.