Examining the Relationship Between Leisure-Time Physical Activity and the Risk of Colon and Breast Cancer: A Methodological Review and Meta-Analyses.

Abstract

Purpose: The objective of this study was to review the methodology and analyze the existing data examining the relationship between leisure-time physical activity and the risk of colon and breast cancer. Methods: Methodological differences (participant characteristics, length of time physical activity was measured, categorizations of quantified physical activity, and assessment instrumentation used to record activity) among studies of activity and cancer risk were reviewed and potential confounding was estimated by calculating the percent difference between multivariate-adjusted effect measures and unadjusted effect measures. A series of meta-analyses were completed. Studies quantifying activity using the Compendium of Physical Activities were included in the primary meta-analyses of colon and breast cancer risk. Subjects from all studies were combined and categorized into low, moderate, and high amounts of weekly activity. Moderate and high groups were compared to the low reference group. Results: Percent differences between adjusted and unadjusted effect measures ranged from 0-31% across all physical activity categories for colon cancer studies and 0-21% for breast cancer studies, with one study reporting a larger difference for each set of analyses (Tang et al., 1999 – 93%; Patel et al., 2003 –64%, respectively). Combined effect measures for high versus low activity ranged from 0.524 (95% CI = 0.348-0.788; p = 0.002; Males) to 0.673 (95% CI = 0.474-0.956; p = 0.027; females) for colon cancer risk. For breast cancer risk, effect measures for high versus low activity were 0.832 (95% CI = 0.747-0.926; p = 0.001) for pre- and postmenopausal females combined, 0.820 (95% CI = 0.584-1.151; p = 0.251) for premenopausal females, and 0.868 (95% CI = 0.754-0.999) for postmenopausal females. Conclusions: Higher amounts of leisure-time physical activity were associated with a reduced risk of male and female colon cancer and postmenopausal breast cancer. Future studies of the relationship between physical activity and cancer risk should adhere to a standardized questionnaire for assessing types of activity, standard time frame for measuring activity, and quantification of the amount of activity likely to be protective, to develop a better understanding of the effects of leisure-time physical activity on cancer risk throughout the lifespan.