In this thesis chronobiological mechanisms in mood disorders are studied in three different parts. First the vulnerability to develop mood disorders is studied by looking at chronotype (being a morning or evening person), genes and mood disorders. There were a number of genes related to mood disorders and to chronotype, but there was no mediating effect. Furthermore, we showed that patients with depressive disorder did not have more social jetlag (the mismatch between internal clock and external rhythm).
The second part studied the direct relationship in rest-activity rhythms and bipolar disorder. We found patients with bipolar disorder are able to maintain a normal rest-activity rhythm outside a mood episode. Furthermore, we showed that sleep disturbances might function as a warning sign for an imminent mood episode. In a detailed study we found that especially in a manic episode sleep disturbances precede the mood episode. Lastly we studied a novel biomarker in activity patterns, which might be able to help diagnose bipolar disorder.
In the third part we showed patients with seasonal affective disorder can be successfully treated with light therapy in the morning. Only one week of light therapy might be enough and there is no need for individual timing of the light on what chronotype the patient is.