How Does Exercise Affect Cancer Risk?
According to statistics from the International Agency for Research on Cancer (IARC), as many as 25% of cancers are due to overweight, obesity, and physical inactivity. Increasing levels of physical activity can potentially ward off several types of cancer.
The links between exercise and cancer prevention are not entirely clear. However, experts have associated increased physical activity and a reduced risk of several specific types of cancer. Studies show, for example, that people who do moderate aerobic exercise for three to four hours per week reduce their risk of colon cancer by 30%. Women who do the same amount of exercise can reduce their risk of breast cancer by as much as 40%. (Some studies suggest that women who meet certain criteria can reduce their breast cancer risk up to 80%.) Evidence also shows that, when compared with sedentary people, active people can reduce their risk of lung cancer (20%), endometrial cancer (30%), and ovarian cancer (20%). Researchers are continually trying to establish similar connections between exercise and other types of cancer.
As is the case with cardiovascular disease, physical activity appears to have an inverse relationship with the types of cancer just listed. That is, the more you exercise, the lower your risk of developing these kinds of cancer. Energy balance also seems to be a factor, at least in relation to a few types of cancer, meaning that people who burn at least as many calories as they take in may further reduce their risk of some cancers. This positive effect may be due to the fact that reducing body fat (through exercise and a healthy diet) lowers the chemical and hormonal activities of adipose (fat) tissue activities that may encourage some cancers to develop.
In addition to reducing the biological influences of adipose tissue, physical activity is known to reduce the inflammatory response and to boost immune function. Chronic inflammation, which can have many causes, leaves body tissues more vulnerable to infection. The immune system is the body’s first line of defense against cancer, so supporting immune function through exercise may help prevent some cancers.
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Emerging data also indicate that physical activity can help improve health outcomes in people who have cancer or are cancer survivors. For example, physical activity appears to restore cardiorespiratory fitness at least to some degree in patients whose heart muscles have been weakened by cancer treatments. This positive outcome was found in 13 separate studies, many of which found significant improvements in heart function among cancer survivors who performed moderate-intensity exercise for 20-40 minutes three times per week.
The benefits were similar across several forms of aerobic exercise, including walking, yoga, and tai chi. Additionally, a handful of studies have found that exercise improves muscular strength and endurance and flexibility in patients whose muscles and joints have been weakened by cancer treatments.
Exercise interventions on health-related quality of life for people with cancer during active treatment. Clinical Otolaryngology 37(5): 390-392. Irwin, M. L., and S. T Mayne. 2008. Impact of nutrition and exercise on cancer survival. Cancer Journal 14(6): 435-441. Morris, G. S., et al. 2009. Pulmonary rehabilitation improves functional status in oncology patients. Archives of Physical Medicine and Rehabilitation 90(5): 837-841. Physical Activity Guidelines Advisory Committee. 2008. Physical Activity Guidelines Advisory Committee Report, 2008. Washington, D.C.: U.S. Department of Health and Human Services. weight if you are currently overweight or obese. Physical activity reduces the risk of cancer of the breast, colon, and uterus, as well as advanced prostate cancer (Figure 12.5). The ACS guidelines encourage everyone to adopt a physically active lifestyle (see the box “How Does Exercise Affect Cancer Risk?”).
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