4,069 children and adolescents aged 8 to 16 years, the prevalence of obesity was highest for those watching four or more hours of television a day and lowest among those watching one hour or less. Other studies have reported associations that were not statistically significant, but all have generally found associations of similar magnitude (reviewed by Robinson, 2001b). Dennison and colleagues (2002) found in a cross-sectional survey that children with televisions in their bedrooms spent an additional 4.6 hours per week watching television or videos. Furthermore, the investigators observed that the prevalence of BMIs greater than the 85th percentile was higher in children with a television in their bedroom than in those without one.
In attempting to determine how television viewing may promote childhood obesity, studies have examined the advertising of foods (particularly high-calorie, high-fat, or high-sugar foods and beverages), eating while watching television, decreased physical activity levels while viewing television, and the potential for physical activity that is lost due to time spent watching. An analysis of commercial advertising during children’s programming time (Saturday morning television, in this study) found that more than half of the commercials (56.5 percent) were for food (Kotz and Story, 1994). A recent review of the literature on food advertising to children found that the four primary categories of food items advertised are breakfast cereals, snacks, candy, and soft drinks (Hastings et al., 2003). Additionally, the authors found a recent trend towards increased advertising by fast food restaurants. Research has shown that television advertising influences children’s food knowledge, choices, and consumption of particular food products, as well as influencing purchase-related behavior and purchasing decisions (Gorn and Goldberg, 1982; Hastings et al., 2003).
Also, as noted earlier in this chapter, watching television during mealtime is associated with decreased intake of fruits and vegetables and increased consumption of soft drinks, salty snacks, pizza, and red meat (Coon et al., 2001). Children report consuming a large proportion of their daily calories while watching television, although there has not been evidence to date that the types or energy densities of foods that children eat while watching television differ significantly from those eaten when not watching (Matheson et al., 2004).
Studies of the nature and extent of associations between increased television viewing and decreased physical activity have produced inconsistent findings—possibly due, in part, to the known limitations of self- and parent-reporting on how children spend their time (Robinson, 2001b). A review by Sallis and colleagues (2000) noted that studies of children ages 4 to 12 had mixed results regarding the associations of sedentary behaviors (specifically, watching television and playing video games) with extent of physical activity, while in teenagers ages 13 to 18, there appeared to be no association. In one study of 191 3- to 4-year-olds that used direct observa-