The Association Between Longitudinal Changes in Body Mass Index and Longitudinal Changes in Hours of Screen Time, and Hours of Physical Activity in German Children.

Introduction: The association of screen time and physical activity with body weight in children has been investigated in cross-sectional and prospective studies, as well as randomized controlled trials. The present study extends previous research by examining how longitudinal within-person changes in screen time and physical activity relate to changes in Body Mass Index (BMI) in children, and how changes in screen time and physical activity relate to each other.

Methods: The data for the present study came from the PIER Youth Study. Data were collected from 971 children and their parents at two time points approximately 1 year apart. A multilevel modeling approach with measurement occasions nested within children was used to model changes in BMI across age.

Results: Within a child, a change in daily hours of TV viewing was associated with a corresponding change in BMI, whereas a change in daily hours of physical activity was associated with an opposite change in BMI. Within-person correlations between changes in screen time and physical activity were small but positive.

Conclusion: The present findings have important implications for interventions to reduce and prevent childhood overweight and obesity. Specifically, interventions should focus on both reducing daily TV viewing and promoting physical activity.