Physical Activity and Cancer

by National Cancer Institute

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.

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.

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.

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. Examples of moderate-intensity and vigorous-intensity physical activities can be found on the CDC Physical Activity Page.

4. 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.

5. 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.

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