Exercise in the prevention and treatment of colorectal neoplasms: effects and mechanisms

Abstract

Objective. This review examines factors that influence the widely varying estimates of protection against colorectal adenomas and cancers associated with occupational and leisure activity, and it seeks a realistic value for use in the formulation of public policy. Attention is also directed to underlying mechanisms, and brief consideration is given to the merits of exercise programmes after the treatment of colorectal tumours.

Methods. The Ovid/Medline data base was searched systematically from January 1996 to November 2015. The terms exercise therapy, physical education/training, athletes, physical fitness and physical activity/motor activity together yielded 205,142 hits, and a combination of the terms colon cancer, rectal cancer, colon adenoma and colon diverticulitis identified 52, 622 unique articles. Combining the 2 searches with a restriction to human subjects identified 286 papers. A review of the abstracts to these articles yielded 3 papers on colorectal adenomas and physical activity, and 41 studies of leisure or occupational activity in relation to colorectal cancer. A further19 articles examined various aspects of the association between colorectal neoplasia and habitual physical activity. This data base was supplemented extensively by articles gleaned from PubMed, Google Scholar and personal files, with a particular emphasis upon occupational studies conducted prior to 1996.

Results. Almost all published research has found an association between physical activity and a reduced risk of colorectal adenomas. Risk ratios for sedentary behaviour have varied widely between studies, with a weighted average of 1.64 for 6 occupational studies, and 1.26 for 27 leisure studies; the relationship is apparently stronger in men than in women. A substantial association with a sedentary lifestyle has also been reported for colon cancers, with a weighted average risk ratio of 1.27 in 39 occupational studies, and of 1.59 in 46 leisure studies. Likewise, for rectal cancers, risk ratios average 1.17 in 27 occupational studies and 1.24 in 20 leisure studies. For both colon and rectal cancers, risk ratios associated with a lack of physical activity were at least as great in women as in men. Inter-study differences in the reported risk-ratios reflect, among other variables, sample size, age, sex and race of subjects, choice of covariates, and the method and timing of activity measurements. Underlying mechanisms of benefit probably vary with the pattern of exercise adopted, but may include a reduced formation of colorectal adenomas, increased colonic motility, increased prostaglandin secretion, an increased use of NSAIDs, dietary changes and avoidance of obesity, a reduced risk of diabetes mellitus and a healthy overall lifestyle. There is growing evidence that an active lifestyle also improves the immediate outcome of colorectal surgery, and that subsequent involvement in an exercise programme enhances functional capacity and quality of life, with a reduced risk of tumour recurrence.

Conclusions. There is now overwhelming evidence that vigorous habitual activity, either at work or in leisure, is associated with a reduced risk of adenomas and cancers of the colon and rectum. However, the reported benefits are based upon very high levels of weekly energy expenditure, and in terms of public policy the general sedentary population seems unlikely either to attain or to maintain such levels of effort; regular moderate physical activity seems unlikely to yield benefits >20% for colon tumours and >10% for rectal tumours.