The relationship of insomnia to mental health; longitudinal findings, importance for depression prevention, and cognitive-behavioural mechanisms.

Abstract

Extensive research has documented the close relationship between sleep disturbance and mental health problems. However, the causal mechanisms at play in this relationship are not yet fully understood. This thesis aims to further understand this relationship through 1) longitudinal analyses, 2) randomised controlled trial design, and 3) exploration of theoretical models, namely cognitive models of insomnia. Section 1 longitudinally explores the relationship between sleep and mental wellbeing in two distinct populations - Indigenous Australian children, and mid-life working adults. Findings from these analyses elucidate crucial links between sleep disturbance and subsequent mental wellbeing in early childhood, and highlight the relevance of family stressors. Secondly, the relevance of work environment to sleep is explored, with Karasek's widely cited model of Job Stress as a guide, and the importance of health and social support in the context of job stress is assessed for both intermittent and chronic sleep disturbance. Section 2 focuses on a large-scale randomised controlled trial (The GoodNight Study) of an online insomnia program and its impact on mental health. This section assesses whether an online intervention targeting insomnia (Shuti) can be used as an effective preventive tool for subsequent depression and was the first trial worldwide to test this preventive utility. Findings from this research, published in The Lancet Psychiatry and British Journal of Psychiatry, Open, indicate that and online insomnia program can indeed effectively prevent depression for some program users, and that this can be seen through to 18-month follow-up. Different trajectories of change in depressive symptoms for two distinct classes of responders are presented in Chapter 2.3. Clinical ramifications of these findings are discussed. Section 3 looks more closely at the mechanisms underlying the links between sleep disturbance and mental health problems addressed in Sections 1 and 2. This is achieved through 1) longitudinal analyses focusing on cognitive-behavioural mechanisms and sleep disturbance, and 2) analyses of cognitive-behavioural mechanisms influencing participant outcomes in The GoodNight Study. Taken together, these two research articles give crucial insights into the impact that pre-exisiting cognitive-behavioural factors might have on sleep, and the importance of understanding cognitive-behavioural mechanisms when designing and interpreting insomnia interventions, particularly when mental health is a target. Again, the relevance of these findings to clinical applications is discussed. Show more