Sedentary Behaviors, TV Viewing Time, and Risk of Young-Onset Colorectal Cancer

BACKGROUND: Colorectal cancer (CRC) diagnosed before age 50 years, or young-onset CRC, is increasing globally with undefined etiology. A sedentary lifestyle is an emerging risk factor for CRC after age 50 years, but its role in young-onset CRC is unknown. METHODS: We prospectively evaluated sedentary behaviors, primarily time watching television (TV), and risk of young-onset CRC among 89 278 women in the Nurses' Health Study II ages 25-42 years at recruitment (1991-2011). We used Cox proportional hazards modelling to estimate relative risks (RR) and 95% confidence intervals (CIs). Statistical tests were two-sided. RESULTS: = .04). Overweight or obese participants may be more susceptible. CONCLUSION: Independent of exercise and obesity, prolonged sedentary TV viewing time, a surrogate for a more inactive lifestyle, was associated with increased risk of young-onset CRC, particularly of the rectum. These findings provide further evidence on the importance of maintaining an active lifestyle.