Physical Activity and Cancer
Untitled Document
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 reduced
risk of cancers of the colon and breast (see Questions 4 and 5).
- Several studies have also reported links between physical activity and
reduced risk of endometrial (lining of the uterus), lung, and prostate cancers
(see Questions 6, 7, and 8).
- Current National Cancer Institute-funded studies are exploring the role
of physical activity in cancer survivorship and quality of life, cancer
risk, and the needs of populations at increased risk (see Questions 9, 10, 11, and 12).
- 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.
- 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).
- 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.
- 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.
- 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).
- 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.
- 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.
- 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).
- 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.
- 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.
- 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.
- 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
- 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.
- 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.
- Slattery, ML. Physical activity and colorectal cancer.
Sports Medicine 2004; 34(4): 239–252.
- IARC Handbooks of Cancer Prevention. Weight Control
and Physical Activity. Vol. 6. 2002.
- 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.
- Lee I, Oguma Y. Physical activity. In: Schottenfeld D,
Fraumeni JF, editors. Cancer Epidemiology and Prevention. 3rd ed.
New York: Oxford University Press, 2006.
- McTiernan A, editor. Cancer Prevention and Management
Through Exercise and Weight Control. Boca Raton: Taylor & Francis
Group, LLC, 2006.
- 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.
- 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.
- 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.
- 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.
- 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.
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