Combined influence of physical activity and television viewing on the risk of overweight in US youth

Objective: The purpose of this study was to examine the combined influence of physical activity ( PA) and television viewing ( TV) on the risk of overweight in US youth ages 14 - 18 years. Research design and methods: Cross- sectional data from a nationally representative sample of approximately 13 600 US high school students participating in the 2001 Centers for Disease Control and Prevention Youth Risk Behavior Survey ( YRBS) were examined. Participants were cross- tabulated into nine PA - TV groups according to the level of moderate ( MPA) or vigorous PA ( VPA) ( low: <= 2 days per week; moderate: 3 - 5 days per week; high: 6 - 7 days per week) and TV ( low: <= 1 h per day; moderate: 2 - 3 h per day; high: >= 4 h per day). The referent group was the low TV/ high PA group. The body mass index was used to determine overweight and obesity based on the International Obesity Task Force reference values. Logistic regression was used to examine the influence of TV and PA on the odds of overweight in boys and girls, while controlling for age and ethnicity. Results: Boys and girls watching low levels of TV did not have increased odds of overweight regardless of PA level with the exception of girls with low TV/ low VPA ( odds ratio ( OR) 1.48). Girls who watched moderate and high levels of TV had increased odds of overweight at any level of MPA or VPA ( OR 1.24 - 3.11). In girls, the odds of overweight increased in a graded manner across PA levels for both the moderate and high levels of TV. Girls with high TV/ low VPA had the highest odds of overweight ( OR 3.11). In general, most of the associations were stronger in girls compared to boys. Conclusion: The results highlight the importance of considering both PA and TV as risk factors for overweight in adolescents.