ABSTRACT
Physical activity and prevention of colo-rectal cancers Observations on physical activity and the prevention of colo-rectal cancer have been based on cross-sectional and case-control studies of populations differing in both the physical demands of occupation and the extent of reported leisure activities. Several authors have measured both of these variables, and in general they have found a closer association of cancer risk with occupational coding than with reported leisure activity.8-11 Most heavy occupational work is characterized by its duration rather than its intensity, and it may be that in terms of countering the development of bowel cancer, prolonged moderate physical activity is more effective than shorter periods of intensive leisure activity. Also, inter-individual differences of occupational activity may be more stable and easier to ascertain than differences in leisure activity. Regular physical activity seems to reduce the risk of colon cancer, but many investigators have found it has less influence upon cancer rates for the rectum (see Tables 9.1 to 9.4). Occupational hazards also seem to affect the risk of colonic and rectal tumours differently.12,13 Probably for this reason, the benefits of physical activity have been less clearly apparent and findings have been more widely divergent when risk ratios for colon and rectal tumours have been considered jointly.8,9,14-18 We will examine in turn associations between physical activity and the risk of cancer in occupational studies for the colon and the rectum and then of leisure studies for the colon and the rectum.
