In a national study of more than one thousand preschool-age children, those who were exposed to more than two hours of television per day were more likely to be overweight at ages 36 and 54 months than those who were exposed to less than two hours of television per day, according to a study in the April issue of Archives of Pediatrics and Adolescent Medicine, a theme issue on children and the media.

The American Academy of Pediatrics recommends that children aged 2 years and older be limited to less than two hours of total media time per day, according to background information in the article. Studies have linked excessive television viewing to a variety of problems, including risk of being overweight. However, most research has focused on school-aged rather than preschool-aged children.

Julie C. Lumeng, M.D., University of Michigan, Ann Arbor, and colleagues studied 1,016 children from 10 urban and rural areas of the United States. The families were recruited shortly after the birth of a child in 1991. Mothers reported how many hours the children were exposed to television--defined as "being awake in the room when the television is on"--on two specific weekdays and two specific weekend days when their children were aged 36 months. Researchers recorded the children's height and weight during visits at age 36 and 54 months, and calculated body mass index (BMI) by dividing weight in kilograms by the square of height in meters. If a child had a BMI that was greater than or equal to the 95th percentile for children of their age and sex, he or she was considered overweight.

Fewer than one-third (31.7 percent, 322 children) were exposed to less than two hours of television per day, while 694 (68.3 percent) were exposed to more than two hours. About 5.5 percent of the children were overweight at the beginning of the study, 5.8 percent at age 36 months and 10 percent at age 54 months. Children exposed to more than two hours of television per day were more likely than those exposed to less than two hours to be overweight at age 36 months and age 54 months. The association between excessive television viewing and weight at age 36 months remained when the researchers considered other factors, including the mother's age, educational level and marital status.

Television exposure could contribute to increased weight in many ways, including through the advertising of unhealthy foods or the tendency of children to snack while watching TV, the authors suggest. Television's effect appears powerful even when children aren't giving it their full attention. "Our findings suggest that exposing children to TV even as 'background noise' while they engage in other activities may increase overweight risk," they conclude. "It may be equally relevant in clinical practice to ask parents how often the child is in the presence of a TV that is 'on' as it is to ask how much time the child spends 'watching TV'."

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(Arch Pediatr Adolesc Med. 2006;160:417-422. Available pre-embargo to the media at jamamedia/.)

Editor's Note: This study was supported by the Fellow-to-Faculty Transition Award and the Midwest Affiliate Grant-in-Aid, both from the American Heart Association, Dallas.

Contact: Krista Hopson
JAMA and Archives Journals