Key Points Physical activity is a critical component of energy balance, the term researchers use to describe how weight, diet, and physical activity influence health. (see Questions 1, 2, and 3) There is strong evidence that physical activity is associated with a reduced risk of cancers of the colon and breast and with improved quality of life among cancer patients. Emerging evidence suggest its role in cancer survival. (see Questions 4 and 5) Several studies also have reported links between physical activity and a reduced risk of prostate, lung, and endometrial (lining of the uterus) cancers. (see Questions 6, 7, and 8) Current NCI-funded studies are exploring the role of physical activity in survivorship and quality of life, cancer risk, and the needs of populations at increased risk. (see Questions 9, 10, 11, and 12)

1. What is physical activity?
   Physical activity is any bodily movement produced by skeletal muscles; such movement results in an expenditure of energy. Physical activity is a critical component of energy balance, a term used to describe how weight, diet, and physical activity influence health, including cancer risk.
   
   
2. How is physical activity related to health?
   Researchers have established that regular physical activity can improve health by:
   
   
   • helping to control weight,
   • maintaining healthy bones, muscles and joints,
   • reducing the risk of developing high blood pressure and diabetes,
   • promoting psychological well-being,
   • reducing the risk of death from heart disease, and
   • reducing the risk of premature death (1).
   
   In addition to these health benefits, researchers are learning that physical activity can also affect the risk of cancer. There is convincing evidence that physical activity is associated with a reduced risk of cancers of the colon and breast (see IARC report under related topics). Several studies also have reported links between physical activity and a reduced risk of cancers of the prostate, lung, and lining of the uterus (endometrial cancer). Despite these health benefits, recent studies have shown that more than 60 percent of Americans do not engage in enough regular physical activity (2).
   
   
3. How much physical activity do adults need?
   The Centers for Disease Control and Prevention (CDC) recommend that adults "engage in moderate-intensity physical activity for at least 30 minutes on five or more days of the week," or "engage in vigorous-intensity physical activity for at least 20 minutes on three or more days of the week." (1). Examples of moderate-intensity and vigorous-intensity physical activities can be found on the CDC Physical Activity Web site(http://www.cdc.gov/nccdphp/dnpa/physical/pdf/PA_Intensity_table_2_1.pdf).
   
   
4. What is the relationship between physical activity and colon cancer risk?
   Colorectal cancer has been the most extensively studied cancer in relation to physical activity, with at least 50 studies examining this association. Many studies in the United States and across the world have consistently found that adults who increase their physical activity either in intensity, duration, or frequency can reduce their risk of developing colon cancer by 30-40 percent, relative to those who are sedentary, regardless of their body mass index (BMI), with the greatest reduction in risk among those who are most active (3-7). The protective effect appears greatest with high-intensity activity, although the optimal exercise levels and duration are still difficult to determine due to differences between studies, making comparisons difficult. It is estimated that 30-60 minutes of moderate to vigorous physical activity per day is needed to protect against colon cancer (6, 7). It is not yet clear at this time whether physical activity has a protective effect for rectal cancer, adenomas, or polyp recurrence (3). Physical activity most likely influences the development of colon cancer in multiple ways. Physical activity may protect against colon cancer and tumor development through its role in energy balance, hormone metabolism, insulin regulation, and by decreasing the time the colon is exposed to potential carcinogens. Physical activity has also been found to alter a number of inflammatory and immune factors, some of which may influence colon cancer risk.
   
   
5. How can physical activity reduce breast cancer risk?
   The association of physical activity with breast cancer incidence has been extensively studied with over 60 studies published in North America, Europe, Asia and Australia. Most studies indicate that physically active women are at lower risk of developing breast cancer than inactive women; however the amount of risk reduction achieved through physical activity varies widely (between 20-80%) (6,7). While most evidence suggests that physical activity reduces breast cancer risk in both premenopausal and postmenopausal women (6), high levels of moderate and vigorous physical activity during adolescence may be especially protective. Although a lifetime of regular, vigorous activity is thought to be of greatest benefit, women who increase their physical activity after menopause may also experience a reduced risk compared to inactive women. A number of studies also suggest that the effect of physical activity may be different across levels of BMI, with the greatest benefit seen in women in the normal weight range (generally a BMI under 25 kg/m-squared) in some studies. Existing evidence shows decreasing risk of breast cancer as the frequency and duration of physical activity increases. Most studies suggest that 30-60 minutes per day of moderate- to high-intensity physical activity is associated with a reduction in breast cancer risk(4, 6). Researchers have proposed several biological mechanisms that may explain the relationship between physical activity and breast cancer development. Physical activity may prevent tumor development by lowering hormone levels, particularly in premenopausal women, lowering levels of insulin and insulin-like growth factor I (IGF-I) improving immune response, and assisting with weight maintenance to avoid a high body mass and excess body fat (7).
   
   
6. How might physical activity reduce endometrial cancer risk?
   About 20 studies have examined the role of physical activity on endometrial cancer risk. The results suggest an inverse association between physical activity and endometrial cancer incidence. These studies suggest that women who are physically active have a 20 percent to 40 percent reduced risk of endometrial cancer (6), with the greatest reduction in risk among those with the highest levels of physical activity. Risk does not appear to vary by age (4). Changes in body mass and changes in the levels and metabolism of sex hormones, such as estrogen, are the major biological mechanisms thought to explain the association between physical activity and endometrial cancer. However, fewer than half of the studies in this area have also adjusted for the potential effect of postmenopausal hormone use, which may increase the risk of endometrial cancer. A few studies have examined whether the effect of physical activity varies according to the weight of the woman, but the results have been inconsistent.
   
   
7. How might physical activity reduce lung cancer risk?
   At least 21 studies have examined the impact of physical activity on the risk for lung cancer. Overall, these studies suggest an inverse association between physical activity and lung cancer risk, with the most physically active individuals experiencing about a 20 percent reduction in risk (4, 6). An analysis of many existing studies found evidence that higher levels of physical activity reduced lung cancer risk, but was unable to fully account for the possible influence of smoking or respiratory disease (6, 10). The relationship between physical activity and lung cancer risk is less clear for women than it is for men.
   
   However, the results of many of these studies are difficult to interpret because smokers who are able to engage in physical activity may have much better lung function. Investigators hypothesize that improvements in pulmonary function and ventilation in active, compared to inactive individuals, may explain the possible association between lung cancer and reduced physical activity.
   
   
8. Does physical activity reduce prostate cancer risk?
   Research findings are less consistent about the effect of physical activity on prostate cancer, with at least 36 studies in North America, Europe and Asia. Overall, the epidemiologic research does not indicate that there is an inverse relationship between physical activity and prostate cancer (4, 7). While it is possible that men who are physically active experience a reduction in risk for prostate cancer, the potential biological mechanisms that may explain this association are unknown, but may be related to changes in hormones, energy balance, insulin-like growth factors, immunity, and antioxidant defense mechanisms (7). One recent study suggested that in men aged 65 or older, regular vigorous activity could slow the progression of prostate cancer (9).
   
   
9. How might physical activity impact cancer survivorship?
   Research indicates that physical activity after a diagnosis of breast cancer may be beneficial in improving quality of life, reducing fatigue (7), and assisting with energy balance. Both reduced physical activity and the side effects of treatment have been linked to weight gain after a breast cancer diagnosis. One study found that women who exercised moderately (the equivalent of walking 3 to 5 hours per week at an average pace) after a diagnosis of breast cancer had improved survival rates compared to more sedentary women. The benefit was particularly pronounced in women with hormone responsive tumors (8). Another study found that a home-based physical activity program had a beneficial effect on the fitness and psychological well-being of previously sedentary women who had completed treatment for early stage through stage II breast cancer. Increasing physical activity may influence insulin and leptin levels and influence breast cancer prognosis. Although there are several promising studies, it is too early to draw any strong conclusions regarding physical activity and breast cancer survival (8).
   
   Two additional studies have suggested a protective association of physical activity after colon cancer diagnosis and survival. Researchers examined the relationship between levels of physical activity both before and after a diagnosis of colon cancer in two different observational studies. While levels of pre-diagnosis physical activity were not related to survival, participants with higher levels of physical activity post-diagnosis were less likely to have a cancer recurrence and had increased survival (11). While these studies suggest protective effects of physical activity, more research is needed to understand what levels of physical activity provide these benefits.
   
   
10. Is NCI exploring the role of physical activity in the quality of life and prognosis of cancer patients?
    NCI-funded studies are exploring the ways in which physical activity may improve the quality of life and prognosis of cancer patients and survivors. One study is evaluating individualized diet and exercise programs to improve the quality of life of patients undergoing treatment for early-stage prostate cancer. Another is examining whether home-based diet and exercise programs help breast cancer patients prevent weight gain and loss of muscle mass. A study is focusing on physical activity interventions for young childhood cancer survivors to examine the impact of these interventions on quality of life and treatment factors. For more information on these and related studies, go to: NCI Cancer Research Portfolio at http://researchportfolio.cancer.gov/.
    
    
11. What are some examples of NCI studies investigating the role of physical activity in cancer risk?
    A number of NCI-funded studies are answering questions about the relationship between physical activity and the risk of developing cancer. NCI has established the Transdisciplinary Research on Energetics and Cancer (TREC) project, which links four research centers investigating how energy balance and physical activity modify the risk of cancer and influence the process of carcinogenesis. The TREC project also incorporates a broad range of scientists ranging from experts in basic biological science to those with expertise in community behavioral interventions to increase physical activity. This combination of scientists and expertise will allow exploration of the role of physical activity across the full spectrum of cancer prevention. The NCI is also funding a number of other studies that focus on physical activity and cancer risk; for example, one study is looking at how gradually increasing physical activity may affect body fat and hormone levels in women at high risk of developing breast cancer.
    
    
12. Do any of these studies focus on special populations who are at increased risk of cancer?
    NCI funds a number of research projects and interventions aimed at helping vulnerable populations reduce their risk of cancer by becoming more active, changing their nutritional behavior, and/or maintaining an optimal weight. Populations included in these projects include multiethnic working poor populations, African-American women, rural communities, overweight or obese individuals, and cancer survivors. For example, one study involving rural churches is exploring methods of helping participants to change their nutrition, activity, and exercise patterns to meet cancer risk reduction guidelines. In other studies, researchers are investigating new methods of telephone and internet-based interventions to increase physical activity in adults living in rural areas. Another example is a study focusing on minority youth in urban areas on mechanisms to incorporate physical activity into their daily routines. Several NCI-funded studies have started examining the factors related to long-term behavior change and increases in physical activity.
    
    NCI is supporting national and regional surveys as well as research methodology development to gain more accurate information on physical activity across all age groups and diverse populations as defined by race, ethnicity, income and other factors known to influence levels of physical activity. This information will help identify groups who may benefit from programs to increase physical activity.

Selected References

(1) National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention. Physical Activity and Health: A Report to the Surgeon General, 1996.

(2) National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention. Physical Activity and Good Nutrition: Essential Elements to Prevent Chronic Diseases and Obesity, 2003.

(3) Slattery, ML. Physical activity and colorectal cancer. Sports Medicine 2004; 34 (4): 239-252.

(4) IARC Handbooks of Cancer Prevention, Volume 6: Weight Control and Physical Activity, 2002.

(5) Ballard-Barbash R, Friedenreich C, Slattery M, Thune I. Obesity and Body Composition. In: Schottenfeld, D and Fraumeni JF, editors. Cancer Epidemiology and Prevention. 3rd ed. New York: Oxford University Press, 2006.

(6) Lee I and Oguma Y. Physical Activity. In: Schottenfeld, D and Fraumeni JF, editors. Cancer Epidemiology and Prevention. 3rd ed. New York: Oxford University Press, 2006.

(7) McTiernan A, editor. Cancer Prevention and Management through Exercise and Weight Control. Boca Raton: Taylor & Francis Group, LLC, 2006.

(8) Holmes MD, Chen WY, Feskanich D, Kroenke CH, Colditz GA. Physical Activity and Survival after Breast Cancer Diagnosis. Journal of the American Medical Association. 2005; 293:2479-2486.

(9) Giovannucci EL, Leiu Y, Leitzmann MF, Stampfer MJ, Willett WC. A Prospective study of physical activity and incident and fatal prostate cancer. Archives of Internal Medicine. 2005; 165: 1005-1010.

(10) Tardon A, Lee WJ, Delgado-Rodriquez M, Dosemeci M, Albanes D, Hoover R, Blair A. Leisure-time physical activity and lung cancer: a meta-analysis. Cancer Causes and Control. 2005; 16: 389-397.

(11) Meyerhardt JA, Giovannucci EL, Holmes MD, Chan AT, Chan JA, Colditz GA, Fuchs CS. Physical activity and survival after colorectal cancer diagnosis. Journal of Clinical Oncology. 2006; 24(22):3527-34.

Related Topics

The following organizations can provide additional resources that readers may find helpful:

• The International Agency for Research on Cancer (IARC), a part of the World Health Organization, convened an international panel of experts in 2001 to conduct a full review of the scientific literature on obesity and cancer. Their findings are published in Volume 6 of the IARC handbooks of cancer prevention (Reference: Vanio H, Bianchini F. IARC handbooks of cancer prevention. Volume 6: weight control and physical activity. Lyon, France: IARC Press; 2002.) To order, call toll-free: 1-877-946-4272 or email: iarcpress@who.int.
  
  
• The CDC's Nutrition and Physical Activity Web site contains information, recommendations, and publications on physical activity. http://www.cdc.gov/nccdphp/dnpa
  
  
• The American Cancer Society's (ACS) Food and Fitness Web site contains information on becoming and staying active. http://www.cancer.org/docroot/PED/ped_3.asp?sitearea=PED
  
  
• The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health (NIH), Physical Activity and Weight Control Web site contains information, tips, and additional resources. http://www.niddk.nih.gov/health/nutrit/pubs/physact.htm
  
  

For more information about cancer, please visit the NCI Web site at http://www.cancer.gov or call NCI's Cancer Information Service at 1-800-4-CANCER (1-800-422-6237; TTY: 1-800-332-8615)

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