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.
   • 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. 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 50 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 at http://www.cdc.gov/nccdphp/dnpa/physical/pdf/PA_Intensity_table_2_1.pdf on the Internet.

4. What is the relationship between physical activity and colon cancer risk?
   

   Colorectal cancer has been one of the most extensively studied cancers in relation to physical activity, with more than 50 studies examining this association. Many studies in the United States and around 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 to 40 percent relative to those who are sedentary regardless of body mass index (BMI), with the greatest risk reduction seen among those who are most active (3–7). The magnitude of the protective effect appears greatest with high-intensity activity, although the optimal levels and duration of exercise are still difficult to determine due to differences between studies, making comparisons difficult. It is estimated that 30 to 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. What is the relationship between physical activity and breast cancer risk?
   

   The relationship between physical activity and 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 have a lower risk of developing breast cancer than inactive women; however, the amount of risk reduction achieved through physical activity varies widely (between 20 to 80 percent) (6, 7). Although 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 with 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 a decreasing risk of breast cancer as the frequency and duration of physical activity increase. Most studies suggest that 30 to 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 to 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 the immune response; and assisting with weight maintenance to avoid a high body mass and excess body fat (7).

6. What is the relationship between physical activity and risk of endometrial cancer?
   

   About 20 studies have examined the role of physical activity on endometrial cancer risk. The results suggest an inverse relationship 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. What is the relationship between physical activity and lung cancer risk?
   

   At least 21 studies have examined the impact of physical activity on the risk of 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 protect against lung cancer, but was unable to fully control for the effects of smoking or respiratory disease in estimating the magnitude of the potential benefit (6, 8). The relationship between physical activity and lung cancer risk is less clear for women than it is for men.

8. What is the relationship between physical activity and risk of prostate cancer?
   

   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). Although it is possible that men who are physically active experience a reduction in risk of 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 regular vigorous activity could slow the progression of prostate cancer in men age 65 or older (9).

9. How might physical activity affect 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 with more sedentary women. The benefit was particularly pronounced in women with hormone responsive tumors (10). 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 (11). 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.

   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. Whereas 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 (12). Although these studies suggest protective effects of physical activity, more research is needed to understand what levels of physical activity provide these benefits.

10. Is the National Cancer Institute (NCI) exploring the role of physical activity in the prognosis and quality of life of cancer patients?
    

    NCI-funded studies are exploring the ways in which physical activity may improve the prognosis and quality of life of cancer patients and survivors. For more information about current research in this area, please visit NCI’s Cancer Survivorship Research Web site at http://cancercontrol.cancer.gov/ocs on the Internet.

11. Is NCI studying 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) initiative, 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 initiative 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. More information about TREC can be found at http://cancercontrol.cancer.gov/trec/ on the Internet.

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. 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 about 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 and Centers for Disease Control and Prevention (1996). Physical Activity and Health: A Report of the Surgeon General. Retrieved June 26, 2009, from: http://www.cdc.gov/nccdphp/sgr/sgr.htm.

2. National Center for Chronic Disease Prevention and Health Promotion and Centers for Disease Control and Prevention (2008). Preventing Obesity and Chronic Diseases Through Good Nutrition and Physical Activity. Retrieved June 26, 2009, from: http://www.cdc.gov/nccdphp/publications/factsheets/Prevention/obesity.htm.

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

4. IARC Handbooks of Cancer Prevention. Weight Control and Physical Activity. Vol. 6. 2002.

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

6. Lee I, Oguma Y. Physical activity. In: Schottenfeld D, 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. Tardon A, Lee WJ, Delgado-Rodriguez M, et al. Leisure-time physical activity and lung cancer: A meta-analysis. Cancer Causes and Control 2005; 16(4):389–397.

9. Giovannucci EL, Liu 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(9):1005–1010.

10. 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(20):2479–2486.

11. Pinto BM, Frierson GM, Rabin C, Trunzo JJ, Marcus BH. Home-based physical activity intervention for breast cancer patients. Journal of Clinical Oncology 2005; 23(15): 3577–3587.
    

12. Meyerhardt JA, Giovannucci EL, Holmes MD, et al. Physical activity and survival after colorectal cancer diagnosis. Journal of Clinical Oncology 2006; 24(22):3527–3534.
    

Additional Resources

The following U.S. Government agencies provide additional helpful information:

• The CDC’s Nutrition and Physical Activity Web site (http://www.cdc.gov/nccdphp/dnpa) contains information, recommendations, and publications on physical activity.
  
  
• The National Institute of Diabetes and Digestive and Kidney Diseases, part of the National Institutes of Health, Physical Activity and Weight Control Web site (http://www.niddk.nih.gov/health/nutrit/pubs/physact.htm) contains information, tips, and resources.

# # #

• Energy Balance: Weight and Obesity, Physical Activity, Diet Home Page ¹
  (http://www.cancer.gov/cancertopics/energybalance)
• Prevention, Genetics, Causes Home Page ²
  (http://www.cancer.gov/cancertopics/prevention-genetics-causes)

How can we help?

We offer comprehensive research-based information for patients and their families, health professionals, cancer researchers, advocates, and the public.

• Call NCI’s Cancer Information Service at 1–800–4–CANCER (1–800–422–6237)
• Visit us at http://www.cancer.gov or http://www.cancer.gov/espanol
• Chat using LiveHelp, NCI’s instant messaging service, at http://www.cancer.gov/livehelp
• E-mail us at cancergovstaff@mail.nih.gov
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Glossary Terms

A tumor that is not cancer. It starts in gland-like cells of the epithelial tissue (thin layer of tissue that covers organs, glands, and other structures within the body).

A substance that protects cells from the damage caused by free radicals (unstable molecules made by the process of oxidation during normal metabolism). Free radicals may play a part in cancer, heart disease, stroke, and other diseases of aging. Antioxidants include beta-carotene, lycopene, vitamins A, C, and E, and other natural and manufactured substances.

Pertaining to biology or to life and living things. In medicine, refers to a substance made from a living organism or its products. Biologicals may be used to prevent, diagnose, treat or relieve of symptoms of a disease. For example, antibodies, interleukins, and vaccines are biologicals. Biological also refers to parents and children who are related by blood.

Body mass index. A measure that relates body weight to height. BMI is sometimes used to measure total body fat and whether a person is a healthy weight. Excess body fat is linked to an increased risk of some diseases including heart disease and some cancers. Also called body mass index.

Cancer that forms in tissues of the breast, usually the ducts (tubes that carry milk to the nipple) and lobules (glands that make milk). It occurs in both men and women, although male breast cancer is rare.

A term for diseases in which abnormal cells divide without control and can invade nearby tissues. Cancer cells can also spread to other parts of the body through the blood and lymph systems. There are several main types of cancer. Carcinoma is a cancer that begins in the skin or in tissues that line or cover internal organs. Sarcoma is a cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Leukemia is a cancer that starts in blood-forming tissue such as the bone marrow, and causes large numbers of abnormal blood cells to be produced and enter the blood. Lymphoma and multiple myeloma are cancers that begin in the cells of the immune system. Central nervous system cancers are cancers that begin in the tissues of the brain and spinal cord. Also called malignancy.

The process by which normal cells are transformed into cancer cells.

Cancer that forms in the tissues of the colon (the longest part of the large intestine). Most colon cancers are adenocarcinomas (cancers that begin in cells that make and release mucus and other fluids).

Cancer that develops in the colon (the longest part of the large intestine) and/or the rectum (the last several inches of the large intestine before the anus).

Any of several diseases in which the kidneys make a large amount of urine. Diabetes usually refers to diabetes mellitus in which there is also a high level of glucose (a type of sugar) in the blood because the body does not make enough insulin or use it the way it should.

The process of identifying a disease, such as cancer, from its signs and symptoms.

The things a person eats and drinks.

Having to do with the endometrium (the layer of tissue that lines the uterus).

Cancer that forms in the tissue lining the uterus (the small, hollow, pear-shaped organ in a woman's pelvis in which a fetus develops). Most endometrial cancers are adenocarcinomas (cancers that begin in cells that make and release mucus and other fluids).

In biology, the state at which the number of calories eaten equals the number of calories used. Energy balance is affected by physical activity, body size, amount of body fat and muscle, and genetics.

A type of hormone made by the body that helps develop and maintain female sex characteristics and the growth of long bones. Estrogens can also be made in the laboratory. They may be used as a type of birth control and to treat symptoms of menopause, menstrual disorders, osteoporosis, and other conditions.

A condition marked by extreme tiredness and inability to function due lack of energy. Fatigue may be acute or chronic.

A blood pressure of 140/90 or higher. High blood pressure usually has no symptoms. It can harm the arteries and cause an increase in the risk of stroke, heart attack, kidney failure, and blindness. Also called hypertension.

One of many chemicals made by glands in the body. Hormones circulate in the bloodstream and control the actions of certain cells or organs. Some hormones can also be made in the laboratory.

The activity of the immune system against foreign substances (antigens).

The condition of being protected against an infectious disease. Immunity can be caused by a vaccine, previous infection with the same agent, or by transfer of immune substances from another person or animal.

The number of new cases of a disease diagnosed each year.

Having to do with inflammation (redness, swelling, pain, and a feeling of heat that helps protect tissues affected by injury or disease).

A hormone made by the islet cells of the pancreas. Insulin controls the amount of sugar in the blood by moving it into the cells, where it can be used by the body for energy.

One of a pair of organs in the chest that supplies the body with oxygen, and removes carbon dioxide from the body.

Cancer that forms in tissues of the lung, usually in the cells lining air passages. The two main types are small cell lung cancer and non-small cell lung cancer. These types are diagnosed based on how the cells look under a microscope.

The time of life when a woman’s ovaries stop producing hormones and menstrual periods stop. Natural menopause usually occurs around age 50. A woman is said to be in menopause when she hasn’t had a period for 12 months in a row. Symptoms of menopause include hot flashes, mood swings, night sweats, vaginal dryness, trouble concentrating, and infertility.

The total of all chemical changes that take place in a cell or an organism. These changes make energy and the materials needed for growth, reproduction, and maintaining health. They also help get rid of toxic substances.

Having an abnormally high, unhealthy amount of body fat.

A type of study in which individuals are observed or certain outcomes are measured. No attempt is made to affect the outcome (for example, no treatment is given).

Being too heavy for one’s height. Excess body weight can come from fat, muscle, bone, and/or water retention. Being overweight does not always mean being obese.

A growth that protrudes from a mucous membrane.

Having to do with the time after menopause. Menopause (“change of life”) is the time in a woman's life when menstrual periods stop permanently.

Having to do with the time before menopause. Menopause ("change of life") is the time of life when a woman's menstrual periods stop permanently.

The likely outcome or course of a disease; the chance of recovery or recurrence.

A gland in the male reproductive system. The prostate surrounds the part of the urethra (the tube that empties the bladder) just below the bladder, and produces a fluid that forms part of the semen.

Cancer that forms in tissues of the prostate (a gland in the male reproductive system found below the bladder and in front of the rectum). Prostate cancer usually occurs in older men.

Having to do with how the mind works and how thoughts and feelings affect behavior.

The overall enjoyment of life. Many clinical trials assess the effects of cancer and its treatment on the quality of life. These studies measure aspects of an individual’s sense of well-being and ability to carry out various activities.

Cancer that forms in the tissues of the rectum (the last several inches of the large intestine closest to the anus).

Cancer that has recurred (come back), usually after a period of time during which the cancer could not be detected. The cancer may come back to the same place as the original (primary) tumor or to another place in the body. Also called recurrent cancer.

A problem that occurs when treatment affects healthy tissues or organs. Some common side effects of cancer treatment are fatigue, pain, nausea, vomiting, decreased blood cell counts, hair loss, and mouth sores.

The extent of a cancer in the body. Staging is usually based on the size of the tumor, whether lymph nodes contain cancer, and whether the cancer has spread from the original site to other parts of the body.

The percentage of people in a study or treatment group who are alive for a certain period of time after they were diagnosed with or treated for a disease, such as cancer. The survival rate is often stated as a five-year survival rate, which is the percentage of people in a study or treatment group who are alive five years after diagnosis or treatment. Also called overall survival rate.

In cancer, survivorship covers the physical, psychosocial, and economic issues of cancer, from diagnosis until the end of life. It focuses on the health and life of a person with cancer beyond the diagnosis and treatment phases. Survivorship includes issues related to the ability to get health care and follow-up treatment, late effects of treatment, second cancers, and quality of life. Family members, friends, and caregivers are also part of the survivorship experience.

An abnormal mass of tissue that results when cells divide more than they should or do not die when they should. Tumors may be benign (not cancer), or malignant (cancer). Also called neoplasm.

The small, hollow, pear-shaped organ in a woman's pelvis. This is the organ in which a fetus develops. Also called womb.