Physical Activity and Cancer: Fact Sheet

Key Points

* 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, the term researchers use to describe how weight, diet, and physical activity influence health.

* There is strong 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 prostate, lung, and endometrial (lining of the uterus) cancers.

* 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.

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.

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.

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.

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 Page.

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

Individuals who are physically active can reduce their risk of developing colon cancer by 40 percent to 50 percent, with the greatest reduction in risk among those who are most active. A decreased risk of colon cancer has been consistently reported for physically active men. Many studies have reported a reduction in colon cancer risk for physically active women. The relationship between physical activity and risk in women, however, has been less consistent.

Physical activity most likely influences the development of colon cancer through multiple, perhaps overlapping, biological pathways. Many researchers believe physical activity aids in regular bowel movements, which may decrease the time the colon is exposed to potential carcinogens. Increased physical activity also causes changes in insulin resistance, metabolism, and hormone levels, which may help prevent tumor development. Physical activity has also been found to alter a number of inflammatory and immune factors, some of which may influence colon cancer risk.

How can physical activity reduce breast cancer risk?

Physically active women have up to a 40 percent reduced risk of developing breast cancer. Most evidence suggests that physical activity reduces breast cancer risk in both premenopausal and postmenopausal women. Although a lifetime of regular, vigorous activity is thought to be of greatest benefit, women who occasionally engage in physical activity 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). For example, a recent major report from the Women's Health Initiative found that among postmenopausal women, walking 30 minutes per day was associated with a 20 percent reduction in breast cancer risk. The health benefits of physical activity were greatest among women who were of normal weight; they experienced a 37 percent decrease in risk. The protective effect of physical activity was not found among overweight or obese women. Researchers have proposed several biological mechanisms that may explain the relationship between physical activity and breast cancer development. Physical activity causes changes in hormone metabolism, body mass, and immune function, which may prevent tumor development.

How might physical activity reduce prostate cancer risk?

Physical activity probably reduces men's risk for prostate cancer by 10 percent to 30 percent. The likely association between physical activity and prostate cancer is based on a small number of studies that evaluated the role of physical activity in men who developed prostate cancer. Most of these studies indicate that inactive men have higher rates of prostate cancer compared to men who are very physically active. While it is probable 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 .

How might physical activity reduce endometrial cancer risk?

Studies also suggest that women who are physically active have a 30 percent to 40 percent reduced risk of endometrial cancer, with the greatest reduction in risk among those who are most active. The possible association between physical activity and endometrial cancer is based on a limited number of studies, some of which indicate that inactive women have higher rates of endometrial cancer compared to physically active women. Changes in body mass and alterations in level and metabolism of sex hormones, such as estrogen, are the major biological mechanisms thought to explain the association between physical activity and 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.

How might physical activity reduce lung cancer risk?

It is possible that individuals who are physically active have a 30 percent to 40 percent reduced risk of developing lung cancer. The possible link between physical activity and lung cancer is based on a limited number of studies that have found higher rates of lung cancer among those who are physically inactive compared to those who are active, after accounting for smoking status. 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.

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 of cancer patients and survivors. One study is examining the feasibility and benefits of a home-based moderate exercise program among breast cancer survivors (home-based). Another is testing the effectiveness of a nurse-directed walking exercise program to mitigate fatigue and maintain physical functioning during treatment for prostate, breast, or colorectal cancer.
For more information on these and related studies, go to: NCI Cancer Research Portfolio

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. For example, one study is investigating whether women who engage in moderate and strenuous physical activity have a reduced risk of endometrial and ovarian cancer, and if strenuous physical activity reduces this risk more than moderate physical activity. Another is examining the effect of one year of moderate aerobic and strength training exercise among patients with colorectal polyps.

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 for 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, African-American church communities, rural church communities, overweight women, overweight men, and adolescents.

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.
NCI is supporting national and regional surveys 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.

http://www.cancer.gov/newscenter/pressreleases/PhysicalActivity