The majority of colorectal cancers arise from precursors called colorectal adenomatous polyps, or colorectal adenomas, which can be removed during a colonoscopy. Although there is extensive evidence supporting an association between higher overall levels of physical activity and reduced risk of colorectal cancer, few studies have focused on the impact of sedentary behavior on colorectal cancer risk.
"Sedentary behavior is emerging as a risk factor for poor health," said Christine L. Sardo Molmenti, PhD, MPH, postdoctoral research fellow in the Department of Epidemiology at Columbia University Mailman School of Public Health in New York. "Even among those who fulfill daily recommendations for physical activity, lengthy periods of sedentary behavior have been associated with early morbidity and mortality, leading to the ‘active couch potato’ paradigm.
"To our knowledge, this study is the first to specifically investigate the association between sedentary behavior and recurrence of colorectal adenomas. Given the substantial increase in risk of colorectal adenoma recurrence (45%) we observed for men with the highest sedentary time, we believe it would be beneficial to see ‘reduce prolonged sitting time’ added to the list of public health recommendations currently in place for health promotion and disease prevention."
Sardo Molmenti and colleagues performed a pooled analysis of participants of two randomized, double-blind, placebo-controlled phase III clinical trials conducted at the University of Arizona Cancer Center in Tucson and the Mel and Enid Zuckerman College of Public Health: The Wheat Bran Fiber Study and the Ursodeoxycholic Acid Trial.
All participants in the trials had one or more colorectal adenomas removed during a colonoscopy conducted in the six months prior to their trial enrollment. Among the participants were 1,730 who had completed a self-administered questionnaire that included questions about leisure, recreational, household, and other categories of activity at enrollment, and had undergone a follow-up colonoscopy.
When the researchers analyzed all the data together, they found no association between activity type and colorectal adenoma recurrence. However, when they examined the data for men and women separately, they found that men who reported spending more than 11.38 hours a day engaged in sedentary behaviors, such as writing, typing or working on a computer, and reading, were 45 percent more likely to experience colorectal adenoma recurrence compared with men who spent fewer than 6.90 sedentary hours a day. No association between sedentary time and colorectal adenoma recurrence was observed for women.
Further analysis showed that men who reported high levels of sedentary behaviors and low levels of participation in recreational activities such as walking, jogging, and playing golf, were 41 percent more likely to experience colorectal adenoma recurrence compared with men who reported low levels of both sedentary behaviors and recreational activity. According to Sardo Molmenti, this confirms that sedentary behavior appears to independently contribute to increased cancer risk beyond the accompanying reduction in physical activity.
The researchers plan to conduct further studies to determine more clearly the role of sedentary behavior in cancer risk. According to Sardo Molmenti, new tools and methods are needed to better classify and quantify sedentary behaviors.
source : http://www.sciencedaily.com/releases/2013/10/131029143002.htm