Physical activity, sedentary behaviour and mental health in Norwegian youths; a longitudinal study

BACKGROUND: Research suggests that the mental health of adolescents is less than optimal. Physical activity (PA) has been positively associated with mental health, while the relationships with sedentary behaviour (SED) has shown negative associations. Previous studies have methodological limitations related to study design and instruments used to measure both PA/SED and mental health. PURPOSE: Explore whether changes in objectively assessed PA [Total PA and moderate to vigorous PA (MVPA)] and SED are associated with mental health problems (MHP) and mental well-being (MWB) among adolescents. METHODS: Longitudinal data was collected from 11 lower secondary schools in three waves between 2016-2018. Baseline participation rate was 60% (599 participants, 54.4% girls, 13.3 years). PA and SED were measured by ActiGraph GT3X+/BT. MHP were measured by the Strengths and difficulties questionnaire, while MWB was measured by the Warwick-Edinburgh Mental Well-being Scale. RESULTS: No associations between PA (Total PA and MVPA) and MHP were found neither for girls nor boys. However, for boys the results showed a positive relationship between change in SED and MWB (p = 0.02) implying that a daily increase in SED of 60 minutes would be equivalent to a 3.2 points higher score in MWB. For girls, there was a modest relationship between change in Total PA and MWB (p = 0.04) CONCLUSIONS: Our data suggest that there may be a gendered pattern in the relationship between PA, SED and mental health among adolescents. Changes in Total PA and MVPA was largely unrelated to MHP in a healthy sample of adolescents. Among boys, an increase in SED was associated with improved MWB. For girls, the relationship with MWB was only apparent through an increase in Total PA. KEY MESSAGES: • The relationships between PA, SED and mental health among adolescents are complex. • SED may provide an arena for supporting MWB depending on the activities undertaken and requires further research.