The effects of child and adolescent physical activity for future mental health outcomes

Abstract

The notion that physical activity (PA) can be a meaningful way to support mental health has been around for decades. The preponderance of research has been conducted in adults however, over time evidence has increasingly pointed toward favourable outcomes in children and adolescents. These formative years constitute a critical period for the development of positive and negative health behaviours and as such, targeting individuals early in the lifespan may instil a propensity toward active living that supports mental health long-term. Public health strategies designed to increase PA in these age groups as a means of supporting population-level mental health should be evidence-based and currently, a sparsity of research focusing on long-term outcomes limits knowledge in this area. Therefore, the purpose of this thesis was to elucidate the association between child and adolescent PA and mental health and specifically, establish the extent to which PA performed during these years may yield protection against depression in future life stages.

Within the present thesis, four research studies are reported. Study 1 comprised a systematic review of the literature wherein it was concluded there was partial evidence that child/adolescent PA is associated with mental health benefits observable at least 12 months later. However, findings to date are heterogeneous with some studies observing associations where others do not. The most consistent evidence was observed for team sport, but this is perhaps due in part to it being the most highly researched form of PA. There was minimal evidence for the comparative effects of PA in different active life domains. Effects for international PA guideline adherence were inconsistent and benefits have also been linked to lesser volumes and intensities of activity. Given that PA guidelines (e.g., those issued by the World Health Organisation or United Kingdom Chief Medical Officers) are often central to public health policy and practice, volume of activity became the central research-focus going forward. Study 2 was the first of three secondary research studies using large-scale birth cohort study data wherein PA trajectories throughout childhood and adolescence, and iii depression in early adulthood were established through Latent Growth Mixture Modelling. Analysis revealed a benefit for the most active class however, the effect was small and differences were inconsistent across classes. Study 3 and Study 4 built on these findings by investigating associations between future depression and PA performed in childhood and adolescence independently. In Study 3 associations between different volumes and intensities of childhood PA and adolescent depression were analysed through a series of regressions and univariate analysis of covariance. When grouped into PA tertiles, no differences in adolescent depression were observed between more and less active children however, within the most active tertile there was a positive association with depression inferring depression increases with activity, but only for the most highly active individuals. When categorised as either meeting or not meeting current PA guidelines, those meeting guidelines were at greater risk of a major depressive episode in adolescence leading to the proposal that differentiating between those who do (not) achieve recommended PA levels as a means of assessing depression risk lacks capacity to capture the diverse needs and drivers of mental health difficulties for particularly active young people. Lastly, Study 4 resumed a person-centred approach whereby Latent Profile Analysis identified 3 distinct groups of adolescents based off their daily volumes of Moderate-to-Vigorous and Light PA. Again, no differences were observed in young adult depression between the most and least active adolescents.

To conclude, evidence presented herein posits that PA endorsed in childhood or adolescence is likely to make minimal difference to the risk of depression long-term. There is potential that childhood PA has a residual benefit for depressive symptoms in early adulthood but not adolescence (according to the results of Study 2 and Study 3, respectively) due to the myriad of competing stressors that impact mental health during this transitionary phase of life. Approaches to public health may also benefit from reorientating toward the ‘some is iv good, more is better’ narrative as opposed to continued emphasis on PA guideline adherence given the guidelines’ limited capacity to identify young people at greater risk of depression long-term. The implications of individual study findings and the collective conceptual, theoretical, and methodological contributions of the thesis are discussed herein.

Date of Award	Jun 2024
Original language	English
Supervisor	Kyle Paradis (Supervisor), Gavin Breslin (Supervisor), Angela Carlin (Supervisor) & Stephen Shannon (Supervisor)