摘要：Objectives . We tested the associations of content types of children's television viewing with subsequent body mass index (BMI) to assess the plausibility of different causal pathways. Methods . We used time-use diary data from the Panel Survey of Income Dynamics to measure television viewing categorized by format and educational and commercial content. Analyses were stratified by age because children younger than 7 years are less able to understand the persuasive intent of advertising. BMI z scores in 2002 were regressed on television viewing, sociodemographic variables, mother's BMI, and BMI in 1997 (for older children only). Results . Among children aged 0 to 6 years in 1997, commercial viewing in 1997 was significantly associated with BMI z scores in 2002 in fully adjusted regressions. Among children older than 6 years, commercial viewing in 2002 was associated with 2002 BMI. These results were robust after adjustment for exercise and eating while watching television. Conclusions . The evidence does not support the contention that television viewing contributes to obesity because it is a sedentary activity. Television advertising, rather than viewing per se, is associated with obesity. Obesity continues to be a major public health concern for America's children, with obesity rates for preschool children tripling in the past 30 years and quadrupling for children aged 6 to 11 years. 1 Television viewing has been shown to be associated with obesity cross-sectionally 2 – 8 and in longitudinal data in many, 9 – 14 but not all, 15 – 17 studies. Comprehensive literature reviews of these disparate results conclude that the association between television viewing and obesity is on average small, but negative. 18 , 19 A constructive way to reconcile the disparate findings is to recognize that different kinds of television content may exert different effects on obesity. Television might lead to obesity through 3 primary pathways 20 , 21 : by displacing time that would otherwise be spent in physical activity; by promoting eating while viewing, which may foster both lower-quality and higher-quantity food intake; and by exposing children to food advertising, which adversely affects their diets. These pathways have quite different implications for the ways different kinds of television content might affect obesity. The hypotheses involving displacement of physical activity and eating while viewing suggest that all types of television have an equal and significant effect on obesity. If the advertising hypothesis is more accurate, only commercial television viewing should be associated with obesity and not noncommercial television or DVD viewing. Of course, all pathways might be operative, in which case we would expect significant associations between all types of content and obesity but associations of greater magnitude for commercial content. A review of the literature on the role of media in childhood obesity identified no scholarly articles analyzing the associations of different types of television content with obesity status in children. 22 We used nationally representative longitudinal data to analyze the effects of different kinds of television content on body mass index (BMI).
