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.
Weight gain. Both reduced physical activity and the side effects of cancer treatment can contribute to weight gain after a cancer diagnosis. In a cohort study (a type of epidemiologic study), weight gain after breast cancer diagnosis was linked to worse survival. In a 2012 meta-analysis of randomized controlled clinical trials examining physical activity in cancer survivors, physical activity was found to reduce both body mass index and body weight .
Quality of life. A 2012 Cochrane Collaboration systematic review of controlled clinical trials of exercise interventions in cancer survivors indicated that physical activity may have beneficial effects on overall health-related quality of life and on specific quality-of-life issues, including body image/self-esteem, emotional well-being, sexuality, sleep disturbance, social functioning, anxiety, fatigue, and pain (33). In a 2012 meta-analysis of randomized controlled trials examining physical activity in cancer survivors, physical activity was found to reduce fatigue and depression and to improve physical functioning, social functioning, and mental health (32).
Recurrence, progression, and survival. Being physically active after a cancer diagnosis is linked to better cancer-specific outcomes for several cancer types (34).
Breast cancer: Consistent evidence from epidemiologic studies links physical activity after diagnosis with better breast cancer outcomes. 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. The potential physical activity benefit with regard to death from breast cancer was most apparent in women with hormone receptor–positive tumors.
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.
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. 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.
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. 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.
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.