Active Voice: Leisure Time Sitting and Cancer Risk
By Alpa V. Patel, Ph.D. and Lynette L. Craft, Ph.D, FACSM
Alpa V. Patel, Ph.D., is a cancer epidemiologist and principal investigator of the Cancer Prevention Study-3 at the American Cancer Society in Atlanta, Georgia. Her research broadly focuses on physical activity, sedentary behavior, obesity and disease risk. More specifically, she is interested in understanding these factors in relation to cancer risk and survival, as well as better quantification of the amount and type of activity needed for optimal health.
Lynette L. Craft, Ph.D., FACSM, is the vice president for evidence-based practice and scientific affairs at ACSM. Her Ph.D. is in kinesiology and she is an adjunct faculty member in the Department of Preventive Medicine at Northwestern University, Feinberg School of Medicine in Chicago, Illinois. Her research focuses on the mental and physical benefits of exercise. Specifically, she examines how intervening on lifestyle factors, such as physical activity and sedentary behavior, are related to chronic disease risk and quality of life in breast cancer survivors.
This commentary presents the views of Drs. Patel and Craft on the topic of a research article which they and their colleagues recently published in the journal Cancer Epidemiology, Biomarkers & Prevention, which has received extensive attention in the public media over the last two weeks.
In recent decades, there has been a dramatic increase in leisure time where people sit while using technology advancements such as computer use, television viewing, transportation and other factors. Many individuals who meet physical activity guidelines are sedentary for the majority of their remaining awake time (they often are referred to as “active couch potatoes”). Thus, in recent years, sitting time has been examined in relation to health outcomes as a distinctly different behavior than physical inactivity. In fact, numerous epidemiologic studies have shown that sitting time is independently associated with higher risk of premature death from any cause and risk of various chronic diseases such as cardiovascular disease, type II diabetes and some types of cancer.
While the benefits of physical activity in relation to cancer prevention are well documented, the evidence to support an association between sitting time and cancer risk is in its infancy. Using data from the American Cancer Society’s Cancer Prevention Study-II (CPS-II) Nutrition Cohort, we conducted a detailed analysis of leisure time spent sitting in relation to total and site-specific cancer risk. This study builds upon previously published work (see: Patel et al., 2010) where we documented an association between sitting time and total mortality in men and women. However, in that study, excess risk of cancer-specific mortality associated with sitting time was observed only in women.
The analysis in this, our current study, is comprised of 69,260 men and 77,462 women on the CPS-II Nutrition Cohort who were cancer free at enrollment in 1992 and have been followed for cancer incidence (the current analysis is with follow-up complete through 2009). During that time, 18,555 men and 12,236 women were diagnosed with cancer. Overall, we observed a 10 percent higher risk of total cancer among women who sat six or more hours versus less than three hours in their leisure time (95 percent CI 1.04-1.17). We further examined risk in 17 individual cancer sites in women and found positive associations between sitting time and multiple myeloma, invasive breast cancer and ovarian cancer. We found no overall association between sitting time and total cancer nor with any of the 15 individual cancer sites examined in men. The lack of any observed associations in men may be a real biologic difference or may be due to some limitation in the data available for this analysis. For example, we lacked occupational sitting time data, but this was likely to have a minimal effect on associations in women, since the vast majority of the women in our study were either retired or never worked outside of the home. The majority of men were retired at study entry, but their sitting patterns at enrollment may not reflect their usual sitting patterns during most of their adult years. Given the potentially long latency period of most cancers, it is possible that we did not capture the relevant sitting time exposure. Thus, as we stated in the conclusions of this recent paper, further research is needed to understand the gender difference in the relationship between sitting time and cancer.
Some physical activity guidelines, including those set forth by ACSM and the American Cancer Society, recommend limiting time spent sitting whenever possible. Nonetheless, there is a need to better understand the benefits of reducing sitting time along with meeting recommended levels of physical activity in relation to optimal health. With the widespread interest in the general public and media to understand the health effects of too much sitting, there may be an opportunity to improve population health via messaging about sitting time, especially among the large proportion that is otherwise physically inactive.