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How might physical activity be linked to reduced risks of cancer?

Physical activity is defined as any movement that uses skeletal muscles and requires more energy than does resting. Physical activity can include working, exercising, performing household chores, and leisure-time activities such as walking, tennis, hiking, bicycling, and swimming.

Physical activity is essential for people to maintain a balance between the number of calories consumed and the number of calories used. Consistently expending fewer calories than are consumed leads to obesity, which scientists have convincingly linked to increased risks of 13 different cancers (1). Additionally, evidence indicates that physical activity may reduce the risks of several cancers through other mechanisms, independent of its effect on obesity.

There is substantial evidence that higher levels of physical activity are linked to lower risks of several cancers (2).

  • Colon cancer: Colon cancer is one of the most extensively studied cancers in relation to physical activity (3). A 2009 meta-analysis of 52 epidemiologic studies that examined the association between physical activity and colon cancer risk found that the most physically active individuals had a 24% lower risk of colon cancer than those who were the least physically active (4). A pooled analysis of data on leisure-time physical activity (activities done at an individual’s discretion generally to improve or maintain fitness or health) from 12 prospective U.S. and European cohort studies reported a risk reduction of 16%, when comparing individuals who were most active to those where least active (5). Incidence of both distal colon and proximal colon cancers is lower in people who are more physically active than in those who are less physically active (6, 7). Physical activity is also associated with a decreased risk of colon adenomas (polyps), a type of colon polyp that may develop into colon cancer (8). However, it is less clear whether physical activity is associated with lower risks that polyps that have been removed will come back (9-11).
  • Breast cancer: Many studies show that physically active women have a lower risk of breast cancer than inactive women; in a 2013 meta-analysis of 31 prospective studies, the average breast cancer risk reduction associated with physical activity was 12% (12). Physical activity has been associated with a reduced risk of breast cancer in both premenopausal and postmenopausal women; however, the evidence for an association is stronger for postmenopausal breast cancer (12-15). Women who increase their physical activity after menopause may also have a lower risk of breast cancer than women who do not (13, 15).
  • Endometrial cancer: Many studies have examined the relationship between physical activity and the risk of endometrial cancer (cancer of the lining of the uterus). In a meta-analysis of 33 studies, the average endometrial cancer risk reduction associated with high versus low physical activity was 20% (16). There is some evidence that the association between physical activity and endometrial cancer risk may reflect the effect of physical activity on obesity, a known risk factor for endometrial cancer (16-18).

For a number of other cancers, there is more limited evidence of a relationship with physical activity. In a study of over 1 million individuals, leisure-time physical activity was linked to reduced risks of esophageal adenocarcinoma, liver cancer, gastric cardia cancer (a type of stomach cancer), kidney cancer, myeloid leukemia, myeloma, and cancers of the head and neck, rectum, and bladder (5). These results are generally corroborated by large cohort studies (19) or meta-analyses (20-22).

Nearly all of the evidence linking physical activity to cancer risk comes from observational studies, in which individuals report on their physical activity and are followed for years for diagnoses of cancer. Data from observational studies can give researchers clues about the relationship between physical activity and cancer risk, but such studies cannot definitively establish that being physically inactive causes cancer (or that being physically active protects against cancer). That is because people who are not physically active may differ from active people in ways other than their level of physical activity. These other differences, rather than the differences in physical activity, could explain their different cancer risk. For example, if someone does not feel well, they may not exercise much, and sometimes people do not feel well because they have undiagnosed cancer.

Exercise has a number of biological effects on the body, some of which have been proposed to explain associations with specific cancers, including:

  • Lowering the levels of hormones, such as insulin and estrogen, and of certain growth factors that have been associated with cancer development and progression (23) [breast, colon]
  • Helping to prevent obesity and decreasing the harmful effects of obesity, particularly the development of insulin resistance (failure of the body's cells to respond to insulin)
  • Reducing inflammation
  • Improving immune system function
  • Altering the metabolism of bile acids, resulting in decreased exposure of the gastrointestinal tract to these suspected carcinogens (24, 25) [colon]
  • Reducing the amount of time it takes for food to travel through the digestive system, which decreases gastrointestinal tract exposure to possible carcinogens [colon]

Sedentary behavior, such as prolonged periods of television viewing, sitting, and lying down, is a risk factor for developing chronic conditions, including cancer, cardiovascular disease, and type 2 diabetes, and for premature death (26, 27). In some studies, the association of sedentary behavior with these outcomes is independent of physical activity—that is, the increased risks of disease associated with being sedentary are not lessened by physical activity. However, in one large meta-analysis (28) an increase in cancer mortality was seen only in those sedentary people with the least physical activity.

The U.S. Department of Health and Human Services 2008 Physical Activity Guidelines for Americans recommends that, for substantial health benefits, adults engage in at least 150 minutes (2 hours and 30 minutes) of moderate-intensity aerobic physical activity, 75 minutes (1 hour and 15 minutes) of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity activity, every week. Aerobic physical activity should be performed in episodes of at least 10 minutes, preferably spread throughout the week. Examples of moderate-intensity and vigorous-intensity physical activities can be found on CDC’s Physical Activity website.

For children and adolescents, the guidelines recommend at least 60 minutes (1 hour) of physical activity daily. Most of the 60 or more minutes a day should be either moderate- or vigorous-intensity aerobic physical activity, and should include vigorous-intensity physical activity at least 3 days a week. As part of their 60 or more minutes of daily physical activity, children and adolescents should include muscle-strengthening physical activity on at least 3 days of the week and bone-strengthening physical activity on at least 3 days of the week.

Selected References
  1. Lauby-Secretan B, Scoccianti C, Loomis D, et al. Body Fatness and Cancer--Viewpoint of the IARC Working Group. New England Journal of Medicine 2016; 375(8):794-798. doi: 10.1056/NEJMsr1606602.

  2. World Cancer Research Fund/American Institute for Cancer Research. Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective. Washington DC: AICR, 2007.

  3. Kruk J, Czerniak U. Physical activity and its relation to cancer risk: updating the evidence. Asian Pacific Journal of Cancer Prevention 2013; 14(7):3993-4003.

    [PubMed Abstract]
  4. Wolin KY, Yan Y, Colditz GA, Lee IM. Physical activity and colon cancer prevention: a meta-analysis. British Journal of Cancer 2009; 100(4):611-616.

    [PubMed Abstract]
  5. Moore SC, Lee IM, Weiderpass E, et al. Association of leisure-time physical activity with risk of 26 types of cancer in 1.44 million adults. JAMA Internal Medicine 2016; 176(6):816-825.

    [PubMed Abstract]
  6. Boyle T, Keegel T, Bull F, Heyworth J, Fritschi L. Physical activity and risks of proximal and distal colon cancers: a systematic review and meta-analysis. Journal of the National Cancer Institute 2012; 104(20):1548-1561.

    [PubMed Abstract]
  7. Robsahm TE, Aagnes B, Hjartåker A, et al. Body mass index, physical activity, and colorectal cancer by anatomical subsites: a systematic review and meta-analysis of cohort studies. European Journal of Cancer Prevention 2013; 22(6):492-505.

    [PubMed Abstract]
  8. Wolin KY, Yan Y, Colditz GA. Physical activity and risk of colon adenoma: a meta-analysis. British Journal of Cancer 2011; 104(5):882-885.

    [PubMed Abstract]
  9. Slattery ML. Physical activity and colorectal cancer. Sports Medicine 2004; 34(4):239-252.

    [PubMed Abstract]
  10. Wolin KY, Tuchman H. Physical activity and gastrointestinal cancer prevention. Recent Results in Cancer Research 2011; 186:73-100.

    [PubMed Abstract]
  11. Colbert LH, Lanza E, Ballard-Barbash R, et al. Adenomatous polyp recurrence and physical activity in the Polyp Prevention Trial (United States). Cancer Causes and Control 2002; 13(5):445-453.

    [PubMed Abstract]
  12. Wu Y, Zhang D, Kang S. Physical activity and risk of breast cancer: a meta-analysis of prospective studies. Breast Cancer Research and Treatment 2013; 137(3):869-882.

    [PubMed Abstract]
  13. Eliassen AH, Hankinson SE, Rosner B, Holmes MD, Willett WC. Physical activity and risk of breast cancer among postmenopausal women. Archives of Internal Medicine 2010; 170(19):1758-1764.

    [PubMed Abstract]
  14. Hildebrand JS, Gapstur SM, Campbell PT, Gaudet MM, Patel AV. Recreational physical activity and leisure-time sitting in relation to postmenopausal breast cancer risk. Cancer Epidemiology, Biomarkers & Prevention 2013; 22(10):1906-1912.

    [PubMed Abstract]
  15. Fournier A, Dos Santos G, Guillas G, et al. Recent recreational physical activity and breast cancer risk in postmenopausal women in the E3N cohort. Cancer Epidemiology, Biomarkers & Prevention 2014; 23(9):1893-1902.

    [PubMed Abstract]
  16. Schmid D, Behrens G, Keimling M, et al. A systematic review and meta-analysis of physical activity and endometrial cancer risk. European Journal of Epidemiology 2015; 30(5):397-412.

    [PubMed Abstract]
  17. Du M, Kraft P, Eliassen AH, et al. Physical activity and risk of endometrial adenocarcinoma in the Nurses' Health Study. International Journal of Cancer 2014; 134(11):2707-2716.

    [PubMed Abstract]
  18. Friedenreich C, Cust A, Lahmann PH, et al. Physical activity and risk of endometrial cancer: The European prospective investigation into cancer and nutrition. International Journal of Cancer 2007; 121(2):347-355.

    [PubMed Abstract]
  19. Behrens G, Matthews CE, Moore SC, et al. The association between frequency of vigorous physical activity and hepatobiliary cancers in the NIH-AARP Diet and Health Study. European Journal of Epidemiology 2013; 28(1):55-66.

    [PubMed Abstract]
  20. Behrens G, Jochem C, Keimling M, et al. The association between physical activity and gastroesophageal cancer: systematic review and meta-analysis. European Journal of Epidemiology 2014; 29(3):151-170.

    [PubMed Abstract]
  21. Behrens G, Leitzmann MF. The association between physical activity and renal cancer: systematic review and meta-analysis. British Journal of Cancer 2013; 108(4):798-811.

    [PubMed Abstract]
  22. Keimling M, Behrens G, Schmid D, Jochem C, Leitzmann MF. The association between physical activity and bladder cancer: systematic review and meta-analysis. British Journal of Cancer 2014; 110(7):1862-1870.

    [PubMed Abstract]
  23. Winzer BM, Whiteman DC, Reeves MM, Paratz JD. Physical activity and cancer prevention: a systematic review of clinical trials. Cancer Causes and Control 2011; 22(6):811-826.

    [PubMed Abstract]
  24. Wertheim BC, Martinez ME, Ashbeck EL, et al. Physical activity as a determinant of fecal bile acid levels. Cancer Epidemiology, Biomarkers & Prevention 2009; 18(5):1591-1598.

    [PubMed Abstract]
  25. Bernstein H, Bernstein C, Payne CM, Dvorakova K, Garewal H. Bile acids as carcinogens in human gastrointestinal cancers. Mutation Research 2005; 589(1):47-65.

    [PubMed Abstract]
  26. Schmid D, Leitzmann MF. Association between physical activity and mortality among breast cancer and colorectal cancer survivors: a systematic review and meta-analysis. Annals of Oncology 2014; 25(7):1293-311.

    [PubMed Abstract]
  27. Biswas A, Oh PI, Faulkner GE, et al. Sedentary time and its association with risk for disease incidence, mortality, and hospitalization in adults: a systematic review and meta-analysis. Annals of Internal Medicine 2015; 162(2):123-132.

    [PubMed Abstract]
  28. Ekelund U, Steene-Johannessen J, Brown WJ, et al. Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women. Lancet 2016; 388(10051):1302-1310.

    [PubMed Abstract]

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