Mood correlates with circadian alignment in healthy individuals

Objective: To determine whether there is a correlation between mood and the alignment between the timing of the circadian pacemaker (circadian phase) and the timing of sleep in healthy, euthymic individuals. Methods: Participants were 25 first-year medical students (25.9 ± 3.3 years, 16 females). Mood (Profile of Mood States, brief form) and circadian phase (salivary dim light melatonin onset) were assessed 4 times over 7 weeks. Circadian alignment was determined using the dim light melatonin onset to average midsleep interval (phase angle difference). Results: Profile of Mood States, brief form score and phase angle difference were correlated: later dim light melatonin onset relative to midsleep (shorter phase angle differences) was associated with worse mood (F_1,75 = 10.953, p = .001). There was no difference in Profile of Mood States, brief form score between female and male participants and no interaction between gender and phase angle difference. Conclusions: There is a correlation between circadian alignment and mood among healthy individuals as has been found in individuals with seasonal and nonseasonal depression. This finding has implications for the development, prevention and treatment of mood disorders.