Abstract A25: Television watching, other sedentary behaviors and colorectal cancer survival in men
Authors: Cao Yin , Meyerhardt Jeffrey , Chan Andrew , Fuchs Charles , Giovannucci Edward 
Published: October 2015

Abstract
Background: Independent of physical activity, television (TV) watching, a major sedentary behavior in the United States, is associated with increased risk of obesity and diabetes, established risk factors for colorectal neoplasia. Although data suggest probable positive associations between sitting time, in particular time spent watching TV, and risk of colorectal adenoma and cancer, the impact of sedentary behaviors on mortality among colorectal cancer patients is unclear.
Methods: We assessed the association between pre- and post-diagnostic time spent sitting while watching TV as well as other sedentary behaviors (other sitting at home and sitting at work/driving) and mortality from colorectal cancer and other causes, as well as overall mortality among nonmetastatic colorectal cancer cases identified between 1986 to 2010 from the Health Professionals Follow-up Study. Starting from 1988, participants reported average weekly time spent sitting watching TV/VCR biennially, and hours of other sitting at home and sitting at work/driving since 1990. For analyses of prediagnosis sedentary behavior, we calculated cumulative hours of sitting to the time of diagnosis to capture long-term sitting behavior. For postdiagnosis analyses, the first assessment collected at least 6 months but no more than 3 years after diagnosis was used to avoid assessment during the period of active treatment. Cox proportional hazards models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs).
Results: A total of 858 and 662 eligible colorectal cancer patients were included in the analysis of prediagnostic and postdiagnostic TV watching, respectively. More time spent sitting watching TV before diagnosis was significantly associated with increased risk of colorectal cancer-specific mortality but not with mortality from other causes or overall mortality in multivariate analyses adjusted for age and years of diagnosis, stage, grade and location of the tumor, and smoking status. Further adjusting for leisure-time physical activity or potential mediators including body mass index and dietary score did not appreciably change the estimates. The HRs (95% CIs) of colorectal cancer-specific mortality across categories of prediagnostic TV watching (0-6, 7-13,14-20, ≥21 h h/wk) were 1.00 (referent), 0.82 (0.55-1.24), 1.13 (0.72-1.76), 2.10 (1.27-3.47) (P for trend=0.01). We combined the first three categories of TV watching based on the dose response relationship (HR for ≥21 vs &lt; 21 h/wk=2.19; 95% CI 1.39-3.44) to assess potential effect modifications, and found that the association was slightly stronger among stage I and II than among stage III cancer patients, and among those with BMI ≥25 kg/m2 than among patients with BMI &lt;25 kg/m2, although interactions were not significant. Similar associations were observed for colon vs rectal cancer, cancer diagnosed before vs after 2000, and those who engaged in &lt;18 vs ≥ 18 MET (Metabolic Equivalent of Task)-hrs per week of physical activity. When restricted to mortality within 5-year after diagnosis, prolonged TV watching before diagnosis was also associated with higher overall mortality (HR for ≥21 vs &lt; 21 h/wk=1.55; 95% CI 1.03-2.35). Other prediagnostic sedentary behaviors including sitting at home or at work/driving were not associated with mortality from colorectal cancer or other causes, as well as overall mortality. With limited power, we also observed that postdiagnostic time spent sitting watching TV was associated with higher but non-significant increased risk of colorectal cancer-specific mortality (HR for ≥21 vs &lt; 21 h/wk=1.57; 95% CI 0.81-3.03).
Conclusion: Prolonged TV watching is associated with higher colorectal cancer-specific mortality independent of leisure-time physical activity. Reducing sedentary behavior, in particular time spent sitting watching TV, may be important in the prognosis of colorectal cancer.
Citation Format: Yin Cao, Jeffrey Meyerhardt, Andrew Chan, Charles Fuchs, Edward Giovannucci. Television watching, other sedentary behaviors and colorectal cancer survival in men. [abstract]. In: Proceedings of the Thirteenth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2014 Sep 27-Oct 1; New Orleans, LA. Philadelphia (PA): AACR; Can Prev Res 2015;8(10 Suppl): Abstract nr A25.