Although links between children’s TV viewing and body fatness are widely espoused, the vast majority of available data are based on cross-sectional designs showing extremely small associations.15
This study assessed cross-sectional and longitudinal associations between girls’ TV viewing and body fatness across ages 7 to 11 years, using epidemiologic (ie, BMI, overweight status) in addition to clinical measures (ie, DXA) of body fatness. Results clearly indicated that prolonged TV viewing in excess of the AAP recommendations increased girls’ risk of overweight across time. In comparison to girls who never exceeded the AAP TV viewing recommendations, girls who exceeded recommendations at ages 7, 9, and 11 years had significantly higher BMI, higher percentage of body fat, and were more likely to be overweight at age 11 and showed significantly greater increases in BMI across ages 7 to 11 years. Furthermore, girls who exceeded recommendations at all ages were 4.7 times more likely to become overweight between ages 7 to 11 years than girls who never exceeded recommendations. Results for BMI and overweight status were independent of lean body mass. The magnitude of these effects suggests that reductions in TV viewing during childhood may have some clinical relevance in the primary prevention of developing excess body fat during childhood.
Our longitudinal findings are remarkably consistent with recent prospective data. In a state-representative sample of 12- to 17-year old children, children who watched more than 2 hours per day of TV at baseline were 2.2 (95% CI = 1.4 to 3.6) times more likely to become overweight after 3 years.20
In a sample of 103 7-year-old Mohawk girls,18
“excessive” television viewing (equivalent to >2 hours per day) at baseline significantly predicted skinfold thickness 2 years later. Furthermore, Jago et al19
found that TV viewing at age 3 to 4 years was significantly and positively associated with higher BMI 2 years later. Results from this study, in combination with previous prospective research, suggest that there is a delayed effect of TV viewing on body fatness that may not be apparent when examining cross-sectional data. Additional evidence of this time-lagged effect is provided by Hancox et al,28
who found that TV viewing between ages 5 to 15 years was associated with increased BMI at age 26 years. In addition to supporting previous research, this study adds to an accumulating body of research on links between children’s television viewing and body fatness by showing that results obtained for indirect measures of body fatness such as BMI are also present when using more objective measure of body fat (ie, DXA).
Findings from this study suggest that limiting children’s TV viewing to 2 or fewer hours each day, as recommended by the AAP, could reduce their future obesity risk. A reduction in the risk of obesity may not reflect reduced TV viewing per se, but rather a reduction in risk behaviors that are linked with TV viewing. There are a number of mechanisms by which TV viewing has been hypothesized to increase disproportionate weight gain during childhood and adolescence. In particular, TV viewing has been hypothesized to (a) displace physical activity,29
(b) alter the likelihood of becoming active or eating healthy foods due to the social-psychological influences of television program content,30
and (c) decrease resting metabolic rate by reducing lean body mass.31
Data are still equivocal regarding the extent to which TV viewing elevates obesity risk through increasing energy intake or reducing energy expenditure. Previous research from this same sample of girls, however, showed that girls who viewed more hours of TV per day consumed more energy-dense snacks.32
Thus, although results from this study and previous research support a significant longitudinal association between TV viewing and children’s risk of increased body fatness and overweight, it should be noted that mechanisms used to explain obesity are multifaceted and complex, and it is unlikely that TV viewing alone will explain substantial amounts of variance in body fatness. Moreover, the interrelations between TV viewing and other risk factors for obesity (eg, overeating, habitual physical inactivity) are also largely unknown, and this further limits our ability to attribute changes in body fatness to watching television.
Results from this study cannot be generalized beyond girls from white, generally middle-class, well-educated families. The relation between TV viewing and obesity may differ across groups as the result of differences in physical activity and dietary habits and the extent to which one negative health behavior (eg, TV viewing) is compensated by more positive health behaviors (eg, physical activity). In generalizing results from this study to broader populations, it also needs to be taken into consideration that certain types of families self-select themselves into health-based research studies and that people who choose to participate do not represent a random cross section of the population. Another limitation of this study is the reliance on mothers’ reports of girls’ TV viewing. Parents may not know how much TV their children watch and may be compelled to provide socially desirable estimates of their children’s TV viewing, leading to underreporting. Unfortunately, no criterion validity data exist that compare the accuracy of self-reports (by child or parent) with that of direct observation, the gold standard. We do know from this study and previous research13,14,18,23
that child and parent reports are only modestly correlated using current instruments, but these data provide evidence only for concurrent validity of the two self-reports, not an estimate of true behavior. In the case of underreporting, however, it is likely that the pattern of underreporting would underestimate the effects of TV viewing because parents of overweight or at-risk children may be more likely to underreport their TV viewing and overreport their physical activity. Given the likelihood of reporting errors, future research should endeavor to use objective measures of TV viewing.
Although there are a number of limitations to this study, the strengths of this study include its longitudinal design, the use of DXA as a measure of body fatness, the consistent pattern of findings across measures, and the ability to control for lean mass in the analyses assessing BMI at the outcome variable. The results indicated that the association between children’s TV viewing and body fatness emerges over the course of a number of years. Among girls who were normal weight at study entry, girls who exceeded the AAP TV viewing recommendations at ages 7, 9, and 11 years were nearly 5 times more likely to become overweight than girls who never exceeded recommendations. Consequently, results from this study clearly speak to the validity of the AAP recommendations of watching no more than 2 hours of TV per day and indicate the necessity of promoting adherence to these guidelines to reduce children’s risk of overweight.21