Examining the bidirectional relationship between physical activity, screen time, and symptoms of anxiety and depression over time during adolescence.

More physical activity (PA) and less screen time (ST) are positively associated with mental health in adolescents; however, research is limited by short-term designs and the exclusion of ST when examining PA. We examined: (a) changes in PA, ST, symptoms of depression, and symptoms of anxiety over four assessments spanning 11years, and (b) bidirectional relationships between initial PA, ST, and symptoms of depression and anxiety as predictors of change in each other during adolescence. Between 2006 and 2010, participants from Ottawa Canada (Time1; N=1160, Mean age=13.54years) completed questionnaires at four points covering the ages from 10 to 21years. Latent growth modeling was used. PA decreased over time whereas ST and symptoms of depression and anxiety increased over time. Controlling for sex, ethnicity, school location, zBMI, birth year, and parents' education, initially higher anxiety was associated with initially higher ST (covariance=.88, p<.05) and initially lower PA (covariance=-6.84, p=.07) independent of initial symptoms of depression. Higher initial depression was associated with higher initial ST (covariance=2.55, p<.05). Increases in anxiety were associated with increases in ST (covariance=.07, p=.06) and increases in depression (covariance=.41, p<.05). Examining bidirectional relationships, higher initial symptoms of depression predicted greater decreases in PA (b=-.28, p<.05). No other significant findings between initial PA, ST, anxiety, or depression were found as predictors of change in each other. Interventions targeting depression around age 13 may be useful to prevent further declines in PA. Similarly, interventions to reduce ST may be beneficial for concurrent reductions in symptoms of depression and anxiety, irrespective of PA.