LEE, I.-M. Physical Activity and Cancer Prevention: Data from Epidemiologic Studies. Med. Sci. Sports Exerc., Vol. 35, No. 11, pp. 1823–1827, 2003.
Purpose: The aim of this paper is to examine whether physical activity plays any role in the prevention of cancer.
Methods: To accomplish this, data from published epidemiologic studies on the relation between physical activity and the risk of developing cancer were reviewed.
Results: The data are clear in showing that physically active men and women have about a 30–40% reduction in the risk of developing colon cancer, compared with inactive persons. Although the data are sparse, it appears that 30–60 min·d−1 of moderate- to vigorous-intensity physical activity is needed to decrease risk. There is a dose-response relation, with risk declining further at higher levels of physical activity. It is also clear that physical activity is not associated with the risk of developing rectal cancer. With regard to breast cancer, there is reasonably clear evidence that physically active women have about a 20–30% reduction in risk, compared with inactive women. It also appears that 30–60 min·d−1 of moderate- to vigorous-intensity physical activity is needed to decrease the risk of breast cancer, and that there is likely a dose-response relation. For prostate cancer, the data are inconsistent regarding whether physical activity plays any role in the prevention of this cancer. There are relatively few studies on physical activity and lung cancer prevention. The available data suggest that physically active individuals have a lower risk of lung cancer; however, it is difficult to completely account for cigarette smoking. There is little information on the role of physical activity in preventing other cancers.
Conclusion: Physical activity is associated with lower risk of developing certain site-specific cancers, in particular colon and breast cancers.
The idea that physical activity may be important in preventing cancer is not a new one. The earliest epidemiologic studies on this topic date back to 1922, when two studies were published (2,19). Both groups of investigators, working independently, examined mortality rates, including cancer mortality rates, among men with different occupations in Australia, England, and the United States. The investigators observed that the cancer mortality rates in these countries declined with increasing physical activity required for the occupation. They proposed a new hypothesis in the etiology of cancer, that “hard muscular work” was important for cancer prevention.
After these two early studies, the hypothesis languished until the 1980s. Subsequently, more than a hundred epidemiologic studies on the role of physical activity and cancer prevention have been published. In this paper, I would like to highlight some of the evidence regarding whether physical activity plays any role in the prevention of cancer, as well as discuss what data are available on the specific details of the physical activity required. This is not intended to be an exhaustive review of the subject; for a comprehensive review, the reader is directed to a recent publication on this topic (6). Instead, the studies cited in this paper are intended to be representative of the larger body of literature and are intended to illustrate the points being made.
The available studies of physical activity and cancer prevention clearly indicate that physical activity has a different association with different site-specific cancers. Therefore, in this paper, the different site-specific cancers will be reviewed separately. Not surprisingly, the most commonly studied cancers in relation to physical activity also are the most commonly occurring cancers in men and women. In 2002, the American Cancer Society estimated that the three most commonly occurring cancers (other than nonmelanoma skin cancer) in men were prostate, lung, and colorectal cancers (30%, 14%, and 11% of all new cases, respectively); for women, they were breast, lung, and colorectal cancers (31%, 12%, and 12% of all new cases, respectively) (5). The association of physical activity with each of these cancers will be discussed below.
Division of Preventive Medicine, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA; and Department of Epidemiology, Harvard School of Public Health, Boston, MA
Address for correspondence: I-Min Lee, M.D., Sc.D., Address: Brigham and Women’s Hospital, Harvard Medical School, 900 Commonwealth Ave. East, Boston, MA 02215; E-mail: email@example.com.
Submitted for publication December 2002.
Accepted for publication June 2003.