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

OBJECTIVE: 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. METHODS: 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). RESULTS: 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. CONCLUSIONS: These findings suggest that obesity prevention efforts should consider both greater physical activity and less recreational screen use as behavioral interventions.