May 20, 2016
An invited commentary, co-written by two UNC Gillings School of Global Public Health researchers and a Gillings School alumna now at Emory University, concurs with the “exciting findings” of a major international study. Those findings “underscore the importance of leisure-time physical activity as a potential risk-reduction strategy to decrease the cancer burden in the United States and abroad.”
Marilie D. Gammon, PhD, epidemiology professor, lead author; first author Lauren E. McCullough, PhD, Gillings School alumna and assistant professor of epidemiology at Emory; and Kathleen M. McClain, MS, epidemiology doctoral student, wrote “The Promise of Leisure-Time Physical Activity to Reduce Risk of Cancer Development,” published online May 16 in JAMA Internal Medicine.
The commentary is in response to “Association of Leisure-Time Physical Activity with Risk of 26 Types of Cancer in 1.44 Million Adults,” also published online May 16 in JAMA IM. In that study, Steven C. Moore, PhD, MPH, of the National Cancer Institute, led U.S. researchers from Harvard Medical School, University of New Mexico, Washington University (St. Louis), George Washington University (Washington, D.C.) and others, as well as international researchers from Sweden, Norway, France and England, in a wide-ranging study of nearly 1.5 million people in the U.S. and Europe, with the goal of determining the association of leisure-time physical activity and the incidence of common types of cancer.
Study participants were ages 19 to 98 years (median 59 years) and about 57 percent female. High levels of activity were associated with lower risks for 13 cancers, including esophageal adenocarcinoma, liver, lung, kidney, gastric cardia, endometrial, myeloid leukemia, myeloma, colon, head and neck, rectal, bladder and breast cancers. Study authors urged health care professionals to emphasize to inactive adults that most associations between cancer and inactivity were evident regardless of body size or smoking history.
Gammon and colleagues noted that by 2030, the global cancer burden is expected to double, with 21.7 million new cases and 13.2 million cancer deaths projected. Those figures are likely underestimates, given current trends toward unhealthy lifestyle behaviors such as poor diet and smoking. Large increases of cancer incidence are expected in developing countries, where there is little money available for health care, and it is particularly in those countries that preventive strategies could reduce the burden of cancer. Almost one-third of adults worldwide are inactive, they note, and the rates of inactivity are rising in low-income countries.
Moore and colleagues’ analysis, the commentary notes, aims “to determine the cancer risks associated with leisure-time physical activity and potential heterogeneity by smoking and body size. Their approach, focusing on 26 different cancer types and exploration of body mass index (BMI) as both a confounder and modifier of the physical activity–cancer association, is innovative and provides clarity to the potentially important role of leisure-time activity in cancer prevention.”
Gammon and colleagues praised the improved statistical precision of Moore’s study. “In this robust study, the authors were able to demonstrate that leisure-time activity was associated with reduced risk of about half the cancer types examined. … The investigators also controlled for well-known cancer-related risk factors, and about 80 percent of the studies used validated measures of physical activity,” they wrote.
The commentary also praised the original study’s examination of the role of BMI in cancer risk, noting that “Moore and colleagues are among the first to provide evidence suggesting that, for some cancers, physical activity may act together with obesity to influence carcinogenesis.” Study participants with BMI of 25 or greater, for instance, could still reduce risk for lung and endometrial cancers by being active. With a global overweight and obesity rate of 40 percent, “physical activity may serve as a promising risk-reduction strategy,” Gammon and colleagues wrote.
While calling the study “innovative” and “exciting,” Gammon and colleagues also urged more research (1) to determine the roles of BMI and other indices of body weight as related to exercise and cancer risk reduction, (2) to help resolve questions regarding the timing, intensity and dose of activity required to diminish cancer risk and (3) to clarify the underlying mechanisms linking physical activity to cancer.