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Title: Modifiable risk factors for depression in adolescence : understanding the causal role of obesity and physical activity
Author: Turner, Nicholas
ISNI:       0000 0004 7432 7380
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2018
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Background: Adolescent depression is a significant burden to individuals, families and healthcare systems. Understanding modifiable risk factors, such as obesity and physical activity (PA), is key to informing preventative strategies. The aim of this project was to examine the causal relationships between obesity, PA and depression in adolescents. Methods: Longitudinal data on obesity, PA and depression in adolescents came from 3 large international cohorts (ALSPAC N=7457, TRAILS N=2230 and NDIT=1294). Linear regression and generalised estimating equations (longitudinal) were used to model effects of obesity on future depression. Cross-lagged structural equation modelling was used to investigate a bi-directional relationship between obesity and depression. Mendelian Randomization analysis was used to address residual confounding. The same analytical approaches were used to examine the association between PA and depression. Partial least squares regression was used to identify aspect(s) of PA important in adolescent depression. SEM was used to investigate the role of biological and psychosocial factors as mediators of the obesity-depression relationship. Results: There was (inconsistent) evidence of a positive relationship between obesity and depression in females; a 1 SD increase in obesity was associated with a 0.035 SD (95% CI 0.003, 0.067) increase in depression at the next time point. There was evidence (in one cohort) that this relationship may be mediated by body image. There was no consistent evidence of any association between PA and subsequent depression (e.g. a 1 SD increase in PA was associated with a -0.006 SD (SE 0.016) decrease in depression at the next time point). Conclusion: Reducing obesity may improve the mental health of adolescent females, alongside having physical health benefits. There is little evidence that increased levels of PA are beneficial for depression. Embedding data collection within existing cohorts approaching adolescence will further research in this area and potentially improve outcomes for future generations.
Supervisor: Wiles, Nicola ; Tilling, Kate ; Heron, Jon Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available