Symptoms of Depression, Physical Activity, and Sedentary Time: Within-Person Relations From Age 6 to 18 in a Birth Cohort.

Objective: To examine the within-person relations between objectively measured physical activity and clinically assessed symptoms of depressive disorders from childhood to late adolescence.

Method: Seven waves of biennially collected data from a Norwegian birth-cohort (n = 873; 53% girls) followed from age 6 to 18 years were used. Accelerometers were used to assess total physical activity, moderate-to vigorous physical activity, and sedentary time, and symptoms of depression were assessed by semi-structured psychiatric interviews. Mediators (athletic self-esteem, body image, sports participation) were captured by questionnaires. Random intercept cross-lagged panel models were estimated to test the within-person relations and their potential mediators.

Results: From ages 14 to 16 and 16 to 18 years, significant within-person relations were found. Decreased levels of total physical activity (PA) and moderate-to-vigorous physical activity (MVPA) predicted more symptoms of depression (PA: 14-16 years: β = -0.08; 16-18 years: β = -0.09; MVPA: 14-16 years: β = -0.10; 16-18 years: β = -0.07). These relations were not evident at earlier ages. From ages 10 to 12 and 14 to 16 years, an increased number of depressive symptoms predicted decreased levels of physical activity (PA: 10-12 years: β = -0.10; 14-16 years: β = -0.14: MVPA: 10-12 years: β = -0.10; 14-16 years: β = -0.17). We found no evidence for within-person relations between sedentary time and depressive symptoms, and no significant sex differences or mediations.

Conclusion: Individuals who increase their physical activity levels from middle to late adolescence are less likely to develop symptoms of depression compared to what they otherwise would. Thus, in this age period, physical activity may protect against depressive symptoms.