Trends in U.S. adolescent physical activity and obesity: A 20-year age-period-cohort analysis

Adolescent obesity can lead to long-term health problems and is a topic of major concern in pediatric and broader medical and public health spheres. Numerous national and state-wide initiatives aimed at increasing physical activity and/or improving nutrition in this age group have assumed the goal of reducing the prevalence adolescent obesity.

We assess trends in U.S. adolescent physical activity and body mass index between 1999 and 2019.

Using data from the U.S. Youth Risk Behaviour Surveillance System, we analyse data from 144 544 14-to-18-year-old respondents. We use multilevel linear and logistic regression to perform age-period-cohort analyses attributing changes in physical activity and body mass index over time to these three sources.

Age and period effects are strong in all outcomes studied. Physical activity consistently decreases with age across the study period. Age trends in obesity have reversed in recent years, with older adolescents now more likely to be have obesity than younger adolescents. Both female and Asian adolescents report less physical activity but lower rates of obesity than their male and non-Asian counterparts.

The reversal of obesity trends by age with little change in physical activity over the study period suggests other lifestyle factors have changed over the study period to increase the prevalence of obesity in older adolescents.