Background: Television (TV) watching, a major sedentary behavior in the United States, has been associated with obesity. We hypothesized that prolonged TV watching may increase risk for type 2 diabetes.
Methods: In 1986, 37 918 men aged 40 to 75 years and free of diabetes, cardiovascular disease, and cancer completed a detailed physical activity questionnaire. Starting from 1988, participants reported their average weekly time spent watching TV on biennial questionnaires.
Results: A total of 1058 cases of type 2 diabetes were diagnosed during 10 years (347 040 person-years) of follow-up. After adjustment for age, smoking, alcohol use, and other covariates, the relative risks (RRs) for type 2 diabetes across increasing quintiles of metabolic equivalent hours (MET-hours) per week were 1.00, 0.78, 0.65, 0.58, and 0.51 (P for trend, <.001). Time spent watching TV was significantly associated with higher risk for diabetes. After adjustment for age, smoking, physical activity levels, and other covariates, the RRs of diabetes across categories of average hours spent watching TV per week (0-1, 2-10, 11-20, 21-40, and >40) were 1.00, 1.66, 1.64, 2.16, and 2.87, respectively (P for trend, <.001). This association was somewhat attenuated after adjustment for body mass index, but a significant positive gradient persisted (RR comparing extreme categories, 2.31; P for trend,.01).
Conclusions: Increasing physical activity is associated with a significant reduction in risk for diabetes, whereas a sedentary lifestyle indicated by prolonged TV watching is directly related to risk. Our findings suggest the importance of reducing sedentary behavior in the prevention of type 2 diabetes.