Leisure-Time Physical Activity Versus Sedentary Behaviour in Relation to Colorectal Adenoma and Cancer: Are these Two Distinct Risk Factors?

Abstract

This literature review provides an up-to-date overview of the evidence relating to the associations of leisure-time physical activity and sedentary behaviour with the risk of colorectal adenoma and cancer. A summary of possible biological mechanisms underpinning these associations is also presented. Leisure-time physical activity and sedentary behaviour are often conceptualised as independent risk factors for colorectal adenoma and cancer. Regular leisure-time physical activity is associated with a 20%–25% reduction in colorectal cancer risk and an estimated 16% reduction in colonic adenoma. The risk estimates are similar for males and females, and for proximal and distal colon cancers. In contrast, the evidence linking physical inactivity to rectal cancer is inconsistent. Epidemiological evidence suggests that television viewing time and occupational sitting are associated with a 54% and 24% increased risk of colon cancer, respectively. Prolonged TV viewing (a commonly measured type of sedentary behaviour) is associated with a 9–16% increased risk of colorectal adenoma, independent of leisure-time physical activity. There is convincing evidence that higher leisure-physical activity is associated with a lower risk of colorectal adenoma and proximal and distal colon cancer; no consistent association emerges for rectal cancer. There is emerging evidence linking sedentary behaviour to risk of colorectal cancer and adenoma. Epidemiological evidence suggests that there may be an interaction between leisure-time physical activity and sedentary behaviour. While it is possible that both exposures contribute to carcinogenesis through similar biological mechanisms, further mechanistic research is required to discern whether there are different biological pathways operating in response to physical activity versus sedentary behaviour.