Evidence is strong that exercise in general promotes and enhances health (Fentem, 1994). Additional studies support the concept that exercise may play a protective role in the development of cancer in some populations. Researchers have found that strenuous exercise more than five hours per week lowered the risk of invasive breast cancer, particularly of estrogen receptor–negative invasive breast cancer, when compared with less activity. These findings were supported even as other cancer risks were controlled for in the study population (National Cancer Institute, 2007).
Multiple observational studies have concluded that the evidence for decreased risk with increased physical activity is convincing for colon and breast cancers, probable for prostate cancers, possible for endometrial and lung cancers, and inconclusive for other cancers (Friedenreich & Orenstein, 2002). Although compelling, some of these studies were confounded by incomplete data or uncontrolled variables; therefore, further research remains important. Possible biologic factors that may play a role in prevention include changes in metabolic and endogenous sex hormone levels, growth factors, decreased obesity, and central body adiposity.
Fentem, P.H. (1996). Benefits of exercise in health and disease. BMJ, 308, 1291–1295. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2540212/pdf/bmj00440-0047.pdf
Friedenreich, C.M., & Orenstein, M.R. (2002). Physical activity and cancer prevention: Etiologic evidence and biological mechanisms [Abstract]. Journal of Nutrition, 132, 34565–34645. Retrieved from http://jn.nutrition.org/content/132/11/3456S.short
National Cancer Institute. (2007). Strenuous long-term physical activity lowers risk of breast cancer. Retrieved from http://www.cancer.gov/cancertopics/prevention/breast/physical-activity0307