CHICAGO - A sedentary lifestyle, as indicated by time spent watching television, is associated with an increased risk for type 2 diabetes; and greater physical activity is associated with a reduced risk, according to an article in the June 25 issue of the Archives of Internal Medicine, a member of the JAMA family of journals.

Frank B. Hu, M.D., and colleagues from the Harvard School of Public Health, Boston, analyzed data on 37,918 men (from the Health Professional's Follow-up Study) aged 40 to 75 years to determine whether prolonged TV watching increases the risk for type 2 diabetes. In 1986, these men were free of diabetes, ardiovascular disease, and cancer, and completed a detailed physical activity questionnaire. Starting from 1988, participants completed questionnaires every two years and reported their level of physical activity and average weekly time spent watching TV.

According to background information in the article, previous studies strongly support the role of exercise in the prevention of type 2 diabetes. However, less attention has focused on sedentary behaviors in relation to risk for diabetes. Television 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 a 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 (a risk factor for diabetes) in children and adults.

In this study, during 10 years of follow-up, 1,058 cases of type 2 diabetes were diagnosed. After adjusting for age, smoking, alcohol use, and other covariates, higher levels of physical activity were associated with a significantly lower risk for type 2 diabetes. Time spent watching TV was significantly associated with a higher risk for diabetes. After adjustment for age, smoking, physical activity levels, and other covariates, compared to men who watched TV 0-1 hours per week, men who watched TV 2-10 hours per week had a 66 percent increased risk for diabetes; 21-40 hours per week, more than twice the risk; and greater than 40 hours per week, nearly three times the risk.

According to the authors, the increased risk of diabetes in men who watch more TV resulted from a number of possible factors. Studies have shown that TV viewing is directly associated with obesity and weight gain likely because of less physical activity and higher intake of calories. Also, the participants in the study who watched more TV also tended to eat more red meat, processed meat, snacks and sweets, and fewer fruits, vegetables and whole grains. This eating pattern, the authors state, which is directly related to advertisements and food cues appearing on TV, may adversely affect diabetes risk.

"Our data provide further evidence that higher levels of physical activity, including moderate-intensity exercise such as walking, are associated with a substantial reduction in risk for diabetes," the authors write. "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." (Arch Intern Med. 2001;161:1542-1548)

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Editor's Note: This study was supported by the National Institutes of Health, Bethesda, Md., and the American Diabetes Association, Alexandria, Va. For more information, contact the JAMA/Archives Media Relations Department at 312/464-5374. For copies of the article, contact the Center for the Advancement of Health at 202.387.2829 or e-mail press@cfah.org