Walking time, sports activity, job type, and body posture during work in relation to incident colorectal cancer: the JACC prospective cohort study.

PURPOSE

An inverse association between physical activity and colorectal cancer (CRC) has been suggested. We aimed to assess the specific and combined effects of leisure-time and occupational physical activities on CRC risk among Japanese adults.

METHODS

Using Cox proportional hazard models, we tested whether walking time, sports activity, body posture during work, and job type-or the combination of these variables-were associated with CRC incidence in a prospective cohort of 26,897 Japanese adults aged 40-79 years.

RESULTS

During a median 17-year follow-up (1990-2009) period, we ascertained 423 incident cases of CRC (267 colon and 156 rectum cancer). Time spent walking suggested a dose-response inverse relationship with CRC risk (p-trend = 0.051). Manual labor was associated with lower CRC risk when compared to office work with HRs (95% CIs) of 0.74 (0.56-0.97) for CRC and 0.68 (0.48-0.96) for colon cancer. Compared to sitting, moving during work tended to be inversely associated with rectal cancer risk, especially after censoring early incident cases within 3 years after baseline; HR (95% CI) = 0.63 (0.40-0.99). Combining walking and job type suggested mutual and synergistic benefits on the risk of colon cancer (p-interaction = 0.03). Compared to office workers walking < 1 h/day, the HR (95% CI) of colon cancer was 0.48 (0.23-0.98), 0.61 (0.42-0.89), and 0.59 (0.41-0.87) in office workers walking ≥ 1 h/day, non-office workers walking < 1 h/day, and non-office workers walking ≥ 1 h/day, respectively.

CONCLUSION

The time spent walking, job type, and posture during work were independently associated with the reduced incident CRC risk among Japanese men and women.