In Canada, colorectal cancer is the second leading cause of cancer death. One of the main risk factors for this cancer is older age; another important risk factor is physical inactivity.
Physical activity may protect against colon cancer because it speeds the passage of food through the gastrointestinal tract. This reduces how long the body is exposed to potential carcinogens (such as bile acids), to hormones which stimulate cell division (mitogens, including insulin-like growth factors or IGF), and to free radicals that damage DNA. Physical activity also increases immune responses by those cells that can kill tumor cells (at least in lab experiments). However, there is little empirical evidence to show exactly how physical activity helps protect against colon cancer in people.
Physical activity helps prevent breast cancer
Many observational studies have shown that physically active women are less at risk of breast cancer than women who are inactive. So far, no research has used randomized controlled trials to prove that exercise causes the reduced risk.
Nevertheless, studies of groups of women have shown that 3 to 4 hours a week of vigorous activity can cut the risk of breast cancer by about 30 to 40%. The risk is reduced even more for postmenopausal women. Women who were physically active as adolescents (at age 12) were less likely to develop breast cancer than women who were less physically active as teenagers.
How exercise affects older cancer survivors
Studies also suggest that aerobic and resistance exercise programs can benefit older prostate cancer survivors, even while they are receiving treatments such as hormone therapy and radiation therapy.
For more information, visit the Active Living Coalition for Older Adults website at http://www.alcoa.ca/.