SUMMARY: The American Cancer Society estimates that in 2016, 1,685,210 new cancer cases will be diagnosed in the United States and 595,690 cancer deaths are projected. It is a well established fact that physical activity reduces the risk of heart disease and all-cause mortality. Additionally, previously published studies have shown reduced risks for Colon, Breast and Endometrial cancers with physical activity. However, it has remained unclear whether physical activity reduces risk of other cancers, which together constitute approximately 75% of all cancers in the United States.
It has been hypothesized that the link between physical activity and cancer is mediated through both hormonal as well as non-hormonal pathways. Hormonal systems such as sex steroids, insulin and insulin-like growth factors, and adipokines can initiate cancer cell growth. Intervention with physical activity by partly reducing adiposity, decreases the levels of estrone, estradiol and insulin in postmenopausal women. Non-hormonal mechanisms linking physical activity to cancer risk, include inflammation, immune function, oxidative stress, and for colon cancer, a reduction in transit time for waste to pass through the gastrointestinal tract.
The authors in this study examined pooled data from 12 prospective cohort studies involving 1.44 million participants, to find out whether there was an association of leisure-time physical activity with incidence of 26 different cancer types. They also examined whether these associations were evident regardless of body size or smoking history. Leisure-time physical activities were defined as activities done at an individual’s discretion, to improve or maintain fitness or health. This could include walking, running, swimming or other moderate- to vigorous-intensity activities. The median physical activity in this study was equivalent to 150 minutes of moderate-intensity activity every week and comparable to the current recommended minimum physical activity level for the US population. Leisure-time physical activity was assessed by self-reported surveys. The median age was 59 years and median BMI was 26.
Participants were followed for a median of 11 years during which period 187,000 new cases of cancer occurred. The authors noted that leisure-time physical activity was associated with lower risk of 13 of 26 cancer types which included Esophageal adenocarcinoma, Liver, Lung, Kidney, Gastric cardia, Endometrial, Myeloid Leukemia, Myeloma, Colon, Head and Neck, Rectal, Bladder and Breast. The greatest risk reduction was noted for Esophageal adenocarcinoma. These associations were evident regardless of body size or smoking history in most cases.
The authors concluded that leisure-time physical activity not only reduces risk of heart disease and risk of death from all causes, but also lowers risk of many types of cancer, regardless of body size or smoking history. Physical activity should therefore be promoted for population-wide cancer prevention and control. Association of Leisure-Time Physical Activity With Risk of 26 Types of Cancer in 1.44 Million Adults. Moore SC, Lee I, Weiderpass E, et al. JAMA Intern Med. 2016;176:816-825.