The interplay between depression, sleep, and type 2 diabetes: Shedding light on

Depression and T2D cluster together, and sleep disturbances have been hypothesized to explain this. Hence, the aim of this thesis was to disentangle the complex interplay between depression, sleep and glycemic control in individuals with T2D. We made progress in the understanding of this interplay, but we also found that the interrelationships are even more complex than anticipated. The constructs of depression and sleep appeared to be multifaceted, but closely related, which stresses once more the complexity of the classification of mental disorders. This thesis underscores that depressive symptoms are associated with sleep problems, and that sleep problems may result in poor glycemic control. We did not find associations between depressive symptoms and poor glycemic control, but instead found that insulin resistance could be promising focus for precision medicine in depression. This thesis also suggests that the general practitioner and psychiatrist should consider light therapy as a treatment option in highly insulin resistant individuals with depression. Above all, this thesis highlights the mind-body connection, with associations between mental health and metabolic health. On the whole, this thesis pleas for an approach in which the improvement of mental and physical health is integrated. Lifestyle factors, including sleep, and rhythmicity, but also diet and exercise, may play a prominent role in such an approach.