Television Watching In Relation To Type 2 Diabetes Mellitus - Brief Article

Nutrition Research Newsletter, July, 2001

Epidemiological evidence strongly supports a role of exercise in the prevention of type 2 diabetes mellitus. However, less attention has focused on sedentary behaviors in relation to risk for diabetes. Television (TV) watching represents a major sedentary behavior in the United States. On average, a male adult spends approximately 29 hours per week watching TV, and a female adult, 34 hours per week. Television watching results in lower metabolic rate compared with other sedentary activities such as sewing, playing board games, reading, writing, and driving a car. In several studies, time spent watching TV has been strongly associated with weight gain and obesity in children and adults. The purpose of this recently published study was to examine weather prolonged TV watching predicts subsequent diabetes risk independent of physical activity in a prospective cohort of men.

The Health Professional's Follow-up Study (HPFS) began in 1986 when 51,529 US health professionals aged 40 to 75 years answered a detailed questionnaire that included a comprehensive diet survey and items on lifestyle practice and medical history. Follow-up questionnaires were sent in 1988, 1990, 1992, 1994, and 1996 to update information on potential risk factors and to identify newly diagnosed cases of diabetes and other diseases. The present study followed up 37,918 men (free of previously diagnosed cardiovascular disease, cancer, or diabetes) for incidence of type 2 diabetes during the subsequent 10 years of the study.

Physical activity was assessed using mailed questionnaires at baseline and every 2 years thereafter. Subjects were asked to report the average amount of time they spent per week on a variety of activities. From this information, weekly energy expenditure in metabolic equivalent hours (MET-hours) was calculated. Any physical activity requiting 6 MET-hours or greater was defined as vigorous. Starting from 1988, subjects reported their average weekly time spent watching TV on the biennial questionnaires. A supplementary questionnaire regarding symptoms, diagnostic tests, and hypoglycemic therapy was mailed to men who indicated on any biennial questionnaire that they had been diagnosed with diabetes.

During 10 years of followup, there were 1058 newly diagnosed cases of type 2 diabetes. Increasing total physical activity score was strongly associated with progressively reduced risk for type 2 diabetes. After adjustment for age, average time spent watching TV was strongly associated with increased risk of type 2 diabetes. These results were independent of body weight. The findings of this study extend the literature showing that regular physical activity is associated with a substantial reduction in risk for type 2 diabetes. The results suggest that the apparent beneficial effect of exercise is not confined to high-risk groups. Contrary to the belief that fitness and physical activity might offset the adverse effects of obesity, the researchers found that men who were obese and physically active had a substantially increased risk for diabetes compared with those who were leaner and inactive. In addition, the researchers found that equivalent energy expenditure from brisk walking or vigorous exercise may confer comparable benefits.

This data provides further evidence that higher levels of physical activity, including moderate-intensity exercise such as walking, are associated with a substantial reduction in risk for type 2 diabetes. In contrast, sedentary lifestyle indicated by prolonged TV watching is directly related to diabetes risk. Although these findings lend further support to current guidelines that promote physical activity, they also suggest the importance of reducing sedentary behavior in the prevention of diabetes.

F. Hu, M. Leitzmann, M. Stampfer, G. Colditz, W. Willett, E. Rimm. Physical Activity and Television Watching in Relation to Risk for Type 2 Diabetes Mellitus in Men. Arch Intern Med 161:1542-1548 (June 2001) [Correspondence: Frank B. Hu, MD, Dept. of Nutrition, Harvard School of Public Health, 665 Huntington Ave, Boston, MA 02115 (E-mail: frank.hu@channing.harvard.edu)].