There is substantial evidence that higher levels of physical activity are linked to a lower risk of several cancers — including breast cancer. Physical activity includes working, exercising, performing household chores, and leisure-time activities such as walking, tennis, hiking, bicycling, and swimming.
Many studies show that physically active women have a lower risk of breast cancer than inactive women. In a 2013 analysis of 31 studies of the correlation of exercise to breast cancer risk reduction, the average reduction associated with physical activity was 12 percent! In contrast, a large study showed an increase in cancer mortality in people who are sedentary.
Physical activity has been associated with a reduced risk of breast cancer in both pre- and postmenopausal women; however, the evidence shows the association is stronger for postmenopausal women. In addition, women who increase their physical activity after menopause may also have a lower risk of breast cancer than women who do not.
I was curious about how exercise was linked to reduced risks of cancer. What I found was that exercise has a number of biological effects on the body and some of them have been proposed to explain the risk reduction:
Exercise lowers the levels of hormones insulin and estrogen, and also lowers certain growth factors that have been associated with cancer development and progression.
Exercise helps to decrease the harmful effects of obesity, particularly the development of insulin resistance.
Exercise improves immune system function.
Physical activity is also beneficial for cancer survivors. A large study found that women who exercised moderately — that is the equivalent of walking three to five hours per week at an average pace — had approximately 40 percent to 50 percent lower risks of breast cancer recurrence, death from breast cancer, and death from any cause compared to more sedentary women. In addition, cancer survivors indicated that exercise helped improve quality of life issues like body image/self-esteem, emotional well-being, sexuality, sleep, anxiety, fatigue, and pain.
Many questions remain about physical activity and cancer. Ongoing clinical trials are examining physical activity and/or exercise interventions in cancer prevention, treatment, and supportive care.
By Amy Schwartz
Amy R. Schwartz is the Senior Director, Fitness and Wellness of the JCC of Greater Baltimore. Amy supervises a staff of 90+ instructors who teach 165 classes per week. Amy holds national certifications in group fitness and personal training, and is certified in multiple Les Mills’ formats, Schwinn Indoor Cycling, and the SHOCKWAVE program and more.