A meta-analysis of the association of physical activity with reduced risk of colorectal cancer

Background: Physical activity may be associated with reduced risk of colorectal cancer. The main aim of this paper is to review the available evidence for a link between exercise and large bowel cancer. Methods: A Cochrane-type methodology was performed. Data extracted included, type of study, type of physical activity measured and the numerical results. The risk ratios (RR) of the studies have been pooled according to the type of study, type of exercise, type of cancer and sex. Pooling was undertaken using fixed effect metaanalysis. A random effect meta-analysis was used where substantial heterogeneity existed. Result: Data from 19 cohort studies showed a statistically significant reduction in the risk of colon cancer in physically active males, RP, being 0.79 (95% CI 0.72 - 0.87) and 0.78 (95% CI 0.68 - 0.91) for occupational and recreational activities, respectively. In women only recreational activities arc protective against colon cancer (RR = 0.71, 95% CI 0.57 - 0.88). Case-control studies showed significantly reduced risks of colon cancer in both sexes irrespective of the type of activity. No protection against rectal cancer is seen in either sex. Conclusion: There is considerablc evidence that physical activity is associated with reduced risk of colon cancer in both males and females.