Characterisation of Circadian Rhythms in Unipolar Major Depressive Disorder

This thesis explored problems with circadian rhythms (the “body clock”) in clinical depression. Overall, it was found that body clock timing is advanced, or “runs early,” during unmedicated depression. The sleep hormone melatonin and stress hormone cortisol were secreted over an hour earlier relative to sleep timing, than in healthy individuals. Earlier melatonin and cortisol secretion were also linked with poorer mood and sleep. In contrast, being an “evening type” was linked with more self-reported cognitive problems. These findings help to explain how current treatments work, and reveal opportunities to develop new treatments for depression.