The April 9 edition of the Journal of the American Medical Association (JAMA) is a theme issue. All the research reports deal with some aspect of obesity, one of the nation's increasingly prevalent health threats. Obesity onset is often insidious: a person doesn't go from being a healthy weight to obese overnight. It can take many years of small changes in behavior to lead to obesity. A new report on data from the venerable Nurses' Health Study at Harvard documents one factor that can increase the risk of obesity. The authors analyzed the association of obesity and type 2 diabetes in women with their amount of usual television viewing and activity levels and found that excess TV is a strong risk factor for excess fatness.
Over 50,000 women, who initially had non-obese BMIs (Body Mass Index) of less than 30, were followed for six years (from 1992 to 1998); they completed questionnaires about their physical activity and sedentary activities at the beginning of the study. Other sedentary activities included sewing, playing board games, reading, writing, sitting at work, and driving. Women included in the study did not initially have either cardiovascular disease or diabetes.
After six years, 7.5% of the women had become obese that is, their BMIs increased to over 30. Women who spent the most time watching TV (over forty hours per week) had nearly twice the risk of becoming obese and developing diabetes than women who spent only minimal tube time (one hour per week or less). The researchers found that excessive TV viewing was correlated with "unhealthy eating habits, increased calorie intake, and decreased energy expenditure."
In a meeting highlighting this JAMA obesity issue, Dr. Frank B. Hu, lead author on the study, noted that unlike some other sedentary activities, TV viewing seems to encourage excessive snacking. He recommended that healthcare providers counsel their patients to limit TV viewing to no more than ten hours per week, to get at least a half hour of moderate physical activity daily, and, when possible, to combine watching television with some physical activity like walking on a treadmill or some other form of exercise.
Ruth Kava, Ph.D., R.D., is Director of Nutrition at the American Council on Science and Health.