Associations of Screen Time and Physical Activity With Body Mass Index in Early Adolescence: A Prospective Cohort Study.

Abstract

This study aimed to prospectively identify the independent, mutually adjusted, and interactive associations of screen time and physical activity with BMI and overweight/obesity risk in adolescents. This study analyzed prospective data from 5356 US adolescents in the Adolescent Brain Cognitive Development (ABCD) Study, Year 2 (2018-2020, ages 11-12) and Year 4 (2020-2022, ages 13-14). Mean daily screen time was 6.1 (±5.2) hours and mean step count was 9265 (±3227) steps in Year 2; 32.7% were classified with overweight/obesity in Year 4. In Poisson regression models examining the exposures mutually adjusted for each other, high screen time (> 8 h/day) was associated with higher risk of overweight/obesity (risk ratio [RR], 1.09; 95% CI, 1.02-1.16; p = 0.013) compared with low screen time (0-4 h/day). In multivariable linear and Poisson regression models, respectively, low step count (1000-6000 steps/day) was associated with higher BMI percentile (coefficient [B], 3.27; 95% CI, 1.54-4.99; p < 0.001) and higher risk of overweight/obesity (RR, 1.23; 95% CI, 1.07-1.40; p = 0.003) compared with high step count (> 12,000 steps/day). No significant interactions were observed between screen time and step count. These findings suggest that obesity prevention efforts should consider both greater physical activity and less recreational screen use as behavioral interventions.