Abstract
Various strategies have been proposed as entry points to promote better mental health and well-being. Among these entry points may be modifiable lifestyle behaviours such as sleep, diet, and exercise. These healthy lifestyle behaviours have shown widespread benefits, however, research has largely focussed on these behaviours in isolation, with little understanding of how these behaviours combine to predict mental health and well-being. The aim of this thesis was to delineate the individual, additive, and synergistic associations of these three modifiable lifestyle behaviours, with mental health and well-being. A large-scale cross-sectional survey was completed by 795 young adults in the United States and New Zealand. Each participant reported on a range of lifestyle habits including sleep quality and quantity, consumption of raw and cooked fruit and vegetables, and exercise habits, along with several measures of mental health (depressive symptoms, anxiety, negative mood) and well- being (life satisfaction, flourishing, vitality, positive mood). Results indicated that each lifestyle behaviour in isolation was associated with lower depression, lower anxiety, and higher psychological well-being. However, when tested against each other in regression models, higher sleep quality was the single largest predictor of mental health and well-being, followed by the consumption of raw fruit and vegetables, then physical activity. There were also several higher-order interactions between the health variables. For example, among those with poorer sleep quality, higher intake of raw fruit and vegetables predicted better mental health and well-being, suggesting that diet can buffer the harms of poor sleep quality. Although the study was correlational, findings suggest that behavioural interventions for improving mental health and well-being should target sleep, secondarily diet, and exercise. If confirmed in intervention research, results of this project may help individuals and clinicians become aware of the simple changes people can make in their daily lives to achieve better mental health and well-being with a specific emphasis on targeting sleep quality.