Role of physical and sedentary activities in the development of depressive symptoms in early adolescence.

Objective: To examine whether levels of physical activity or sedentary activity are risk factors for the development of depressive symptoms in early adolescence.
Methods: A representative sample of 2,464 12- to 15-year-old adolescents living in the middle of Norway was assessed twice, during the years 1998 (T1) and 1999/2000 (T2). The attrition rate was 4.3%. We assessed depressive symptoms (using the Mood and Feelings Questionnaire, MFQ) and levels of physical and sedentary activities at baseline and follow-up. Various potentially confounding factors, including demographic factors, were assessed at baseline.
Results: The MFQ scores at T1 were cross-sectionally associated with low levels of vigorous exercise. A possible buffering effect of vigorous exercise on the relationship between stressful life events and depression was demonstrated. In longitudinal analysis low levels of vigorous exercise and high levels of sedentary activities (boys only) predicted a high score (MFQ ≥ 25) at T2.
Conclusions: Low levels of vigorous exercise and high levels of sedentary activities (boys only) constituted independent risk factors for the development of a high level of depressive symptoms in a 1-year study of young adolescents. This knowledge should be considered by policy makers, preventative services, and health-care professionals.