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Title: Television watching and other sedentary behaviors in relation to risk of obesity and type 2 diabetes mellitus in women

Authors: FB Hu, TY Li, GA Colditz, WC Willett, JE Manson

Reviewer: Robert Goldberg, PhD

Reference: JAMA 2003;289: 1785-1791.

Problem addressed: Development of type 2 diabetes mellitus and obesity in middle-aged women.

Purpose of study: To examine the association between various sedentary behaviors, particularly prolonged television watching, and risk of obesity and type 2 diabetes in middle-aged women.

Location of study: Boston, MA

Study design: Prospective epidemiologic investigation (Nurses Health Study).

Results: Women participating in the large prospective Nurses Health Study comprised the study sample. After excluding women with diagnosed CVD, cancer, or diabetes (and women with obesity for the obesity subgroup analyses), more than 50,000 women were surveyed in 1992 with regard to their sedentary behaviors and physical activity profile. The sedentary behaviors consisted of the average amount of time spent weekly watching television, and sitting at work or away from home. An extensive physical activity questionnaire was sent to survey respondents in 1992, 1994 and 1996. With regards to the study endpoints, body weight was measured based on self-reports to the biennial questionnaire that was sent to participating women and body mass index was calculated from this information. Diabetes was diagnosed on the basis of reported symptoms, results of diagnostic tests, and use of hypoglycemic therapy.

Over the 6 years of follow-up, approximately 8% of the middle-aged to elderly women (aged 30-55 years during the initial survey year of 1976) who were not obese (BMI >30) at baseline became obese by 1998. The amount of time spent watching TV was positively associated with the development of obesity. The age adjusted risks of developing obesity were 1.23, 1.42, 1.68 and 2.0, respectively, (compared to women watching 0-1 hours of TV per week) for women watching 2-5, 6-20 21-40, and >40 hours of television weekly. During the 6 years of follow-up, 1515 newly diagnosed cases of type 2 diabetes were diagnosed. After adjustment for age, the risk of developing diabetes increased progressively with the number of hours spent watching television per week. However, the risk of developing diabetes was considerably attenuated after adjusting for BMI, suggesting that the increased risk of diabetes associated with television watching was at least partially mediated through obesity.

Comments: The results of this large prospective study suggest that a number of sedentary behaviors, particularly watching television, were associated with an increased risk of obesity and type 2 diabetes. While a variety of mechanisms may be involved in these deleterious associations, the present results have important current public health implications. These findings are particularly salient in the U.S. population where the prevalence of obesity and type 2 diabetes have increased dramatically over time. Adults, adolescents, and young children should be encouraged to exercise more, and watch less television, to improve their BMI, reduce their risk of diabetes and other chronic diseases, and feel more healthy and full of energy.

Citations:

1. Fiegal KM, Carroll MD, Ogden CL, Johnson CL. Prevalence and trends in obesity among US adults, 1999-2000. JAMA:288:1723-1727.