PURPOSE: The purpose of this study was to examine the associations between lifestyle behavior variables such as physical activity, television watching, computer use, and school night sleep duration with Body Mass Index percentile (BMI%) using quantile regression within a representative sample of adolescents who completed the 2017 US National Youth Risk Behavior Survey (YRBS).
METHODS: A multi-stage cluster sampling procedure obtained a representative sample of US adolescents. The target population consisted of public and private high schoolers from grades 9 through 12. The number of sampled adolescents submitting questionnaires with BMI% data was 13,146. To examine the associations between lifestyle behaviors and BMI%, simultaneous quantile regression was employed. Relationships were modeled at 10 percentile increments and examined independent variables on the continuous measurement scale to determine how the parameter estimates (b-coefficients) vary across percentiles. Post hoc analysis involved modeling the relationships across BMI%’s interquartile range, specifically at the 25^th, 50^th, and 75^th percentiles, in addition to using independent variables treated on the categorical measurement scale.
RESULTS: When relationships were modeled at every 10^thpercentile, more precise parameter estimates were observed at higher percentiles. Across the interquartile range, physical activity associated with lower BMI% at the 50^th and 75^th percentiles (b_range= -2.27% to -5.24%, p<0.05), television watching associated with higher BMI% at the 25^th to 75^th percentiles (b_range=2.29% to 4.16%, p<0.05), sleep durations less than 8 hours per school night associated with higher BMI% at the 25^th and 50^th percentile (b_range=2.81% to 8.26%, p<0.05), and 10 or more hours of school night sleep associated with higher BMI% at the 50^th and 75^th percentile (b_range=3.43% to 7.53%, p<0.05).
CONCLUSIONS: Higher levels of physical activity associated with lower BMI% and longer time watching television, school night sleep durations less than 8 hours, and school night sleep durations of 10 hours or more at higher quantiles associated with higher BMI% in adolescents. Estimates of association were more precise within higher quantiles.