Sedentary behaviors and light-intensity activities in relation to colorectal cancer risk.

A recent meta-analysis found that sedentary behaviors are associated with an increased colorectal cancer (CRC) risk. Yet, the finding on TV viewing time, the most widely used surrogate of sedentary behaviors, was based on only two studies. Furthermore, light-intensity activities (e.g., standing and slow walking), non-sedentary by posture but close to sedentary behaviors by Metabolic Equivalent Task values, have not been investigated in relation to CRC risk. Thus, we prospectively analyzed the relationships based on 69,715 women from Nurses' Health Study (1992-2010) and 36,806 men from Health Professionals Follow-Up Study (1988 - 2010). Throughout follow-up, time spent on sedentary behaviors including sitting watching TV and on light-intensity activities were assessed repeatedly; incidence of CRC was ascertained. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards models from each cohort. A total of 1,119 and 913 incident cases were documented from women and men, respectively. The multivariable HR comparing ≥ 21 versus < 7 hr/week of sitting watching TV was 1.21 (95% CI = 1.02 to 1.43, ptrend =.01) in women and 1.06 (95% CI = 0.84 to 1.34, ptrend =.93) in men. In women, those highly sedentary and physically less active had an approximately 41% elevated risk of CRC (95% CI = 1.03 to 1.92) compared with those less sedentary and physically more active. The other sedentary behaviors and light-intensity activities were not related to CRC risk in women or men. In conclusion, we found that prolonged sitting time watching TV was associated with an increased CRC risk in women but not in men.