Relationship between Physical Activity and Cancer

Relationship between Physical Activity and Cancer

Making moderate to vigorous physical activity a part of your lifestyle lowers your risk of cancer and that of other chronic diseases, such as heart disease and diabetes. Moderate to vigorous physical activity is exercise that makes you sweat and your heart beat faster. It includes walking, swimming, cycling, or running. A growing body of research suggests that doing any kind of activity to avoid too much sitting can help lower cancer risk.

Colon cancer is one of the most extensively studied cancers in relation to physical activity. Studies that examined the association between physical activity and colon cancer risk found that the most physically active individuals had a 24% lower risk of colon cancer than those who were the least physically active . A pooled analysis of data on leisure-time physical activity (activities done at an individual’s discretion generally to improve or maintain fitness or health) from 12 prospective U.S. and European cohort studies reported a risk reduction of 16%, when comparing individuals who were most active to those where least active.

Incidence of both distal colon and proximal colon cancers is lower in people who are more physically active than in those who are less physically active . Physical activity is also associated with a decreased risk of colon adenomas (polyps), a type of colon polyp that may develop into colon cancer. However, it is less clear whether physical activity is associated with lower risks that polyps that have been removed will come back.

Many studies show that physically active women have a lower risk of breast cancer than inactive women and the average breast cancer risk reduction associated with physical activity was 12% . Physical activity has been associated with a reduced risk of breast cancer in both premenopausal and postmenopausal women; however, the evidence for an association is stronger for postmenopausal breast cancer. Women who increase their physical activity after menopause may also have a lower risk of breast cancer than women who do not.

For a number of other cancers, there is more limited evidence of a relationship with physical activity. In a study of over 1 million individuals, leisure-time physical activity was linked to reduced risks of esophageal adenocarcinoma, liver cancer, gastric cardia cancer (a type of stomach cancer), kidney cancer, myeloid leukemia, myeloma, and cancers of the head and neck, rectum, and bladder. These results are generally corroborated by large cohort studies or meta-analyses. Nearly all of the evidence linking physical activity to cancer risk comes from observational studies, in which individuals report on their physical activity and are followed for years for diagnoses of cancer.
Data from observational studies can give researchers clues about the relationship between physical activity and cancer risk, but such studies cannot definitively establish that being physically inactive causes cancer (or that being physically active protects against cancer).

That is because people who are not physically active may differ from active people in ways other than their level of physical activity. These other differences, rather than the differences in physical activity, could explain their different cancer risk. For example, if someone does not feel well, they may not exercise much, and sometimes people do not feel well because they have undiagnosed cancer.

Research indicates that physical activity may have beneficial effects for several aspects of cancer survivorship--specifically, weight gain, quality of life, cancer recurrence or progression, and prognosis (likelihood of survival). Most of the evidence for the potential benefits of physical activity in cancer survivors comes from people diagnosed with breast, prostate, or colorectal cancer. Another prospective cohort study found that women who had breast cancer and who engaged in recreational physical activity roughly equivalent to walking at an average pace of 2 to 2.9 mph for 1 hour per week had a 35% to 49% lower risk of death from breast cancer compared with women who engaged in less physical activity).

Findings from epidemiologic studies cannot completely exclude reverse causation as a possible explanation of the link between physical activity and better cancer outcomes. That is, people who feel good are more likely to exercise and be physically active than people who do not feel good.

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