Breast cancer: Consistent evidence from epidemiologic studies links physical activity after diagnosis with better breast cancer outcomes.35,36 For example, a large cohort study found that women who exercised moderately (the equivalent of walking 3 to 5 hours per week at an average pace) after a breast cancer diagnosis had approximately 40% to 50% lower risks of breast cancer recurrence, death from breast cancer, and death from any cause compared with more sedentary women.37 The potential physical activity benefit with regard to death from breast cancer was most apparent in women with hormone receptor–positive tumors.37
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.38
Colorectal cancer: Evidence from multiple epidemiologic studies suggests that physical activity after a colorectal cancer diagnosis is associated with reduced risks of dying from colorectal cancer.39 In a large prospective cohort of patients with colorectal cancer, those who engaged in leisure-time physical activity had a 31% lower risk of death than those who did not, independent of their leisure-time physical activity before diagnosis.40
Prostate cancer: Limited evidence from a few epidemiologic studies has suggested a possible link between physical activity and better outcomes among men diagnosed with prostate cancer. In one study, men with nonmetastatic prostate cancer who engaged in vigorous activity for at least 3 hours per week had a 61% lower risk of death from prostate cancer compared with men who engaged in vigorous activity for less than 1 hour per week.41 Another study of men with localized prostate cancer found that higher levels of physical activity were associated with reduced overall and prostate cancer–specific mortality.42
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.
What additional research is under way on the relationship between physical activity and cancer?
Many questions remain to be answered in several broad areas of research on physical activity and cancer:
- Although the evidence for causal link is strong for a few cancers, for others it is not, and the question of causality remains an important one. That is, does being physically inactive cause cancer and/or does being physically active prevent cancer?
- If the association is causal, what is the optimal time in life, intensity, duration, and/or frequency of physical activity needed to reduce the risk of cancer, both overall and for specific sites?
- Do biomarkers of cancer risk or progression that are affected by physical activity exist?
- Does the association between physical activity and cancer differ in populations that have higher proportions of inactive and/or obese individuals compared with the general population?
- Does physical activity benefit people with a genetic susceptibility to cancer?
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Source: National Cancer Institute.