Sedentary work and the risks of colon and rectal cancer by anatomical sub-site in the Canadian census health and environment cohort (CanCHEC).

Background: Sedentary behaviour is a potential risk factor for colorectal cancer. We examined the association between sedentary work, based on body position, and colorectal cancer risk in Canadians.

Methods: A working body position category (a. sitting; b. standing and walking; c. sitting, standing, and walking; d. other) was assigned to occupations reported by 1991 Canadian Census respondents based on national occupational counselling guidelines. Adjusted hazard ratios (HRs) and 95% confidence intervals (CI) were estimated for cancers of the colon (overall, proximal, and distal) and rectum in men and women newly diagnosed from 1992 to 2010.

Results: Compared to "sitting" jobs, men in occupations with "other" (non-sitting, -standing, or -walking) body positions had a weakly significant reduced colon cancer risk (HR=0.93, 95% CI: 0.89, 0.98) primarily attributed to protection at the distal site (HR=0.90, 95% CI: 0.84, 0.97). Men in "standing and walking" and "sitting, standing, and walking" jobs did not have significantly reduced colon cancer risks. No effects were observed for rectal cancer in men or colon and rectal cancer in women.

Conclusion: The two significant findings of this analysis should be followed-up in further investigations with additional information on potential confounders. Null findings for rectal cancer were consistent with other studies.