Melatonin Circadian Phase Timing and Stability: Associations With Mood Symptoms Among a Clinically-Enriched Sample of Young Adults With Mood Disorders.

Circadian rhythms regulate many aspects of human health, and disruptions in these rhythms have been implicated in mood disorders. Dim light melatonin onset (DLMO) provides a gold standard measure of circadian timing, yet few studies have examined its stability or relation to mood symptoms in psychiatric populations. This study examined DLMO across three time points over 20 days in a clinically-enriched sample of 124 young adults with and without mood disorders. Participants also reported mood symptom levels three times daily via ecological momentary assessments (EMA). Circadian timing and stability were quantified and their associations with mood symptoms and diurnal mood patterns were assessed. Overall, DLMO demonstrated substantial stability, and did not differ by diagnostic group. The mood disorder group had earlier circadian timing than healthy controls. Hypomanic, but not depressive, symptoms were consistently associated with later DLMO in both cross-sectional and prospective analyses. Moreover, hypomanic symptoms exhibited a diurnal pattern that differed for participants with earlier and later circadian timing. Future work should examine endogenous circadian rhythms in relation to mood disorder subtypes and mood episodes to determine whether circadian timing changes can be used to predict or intervene on psychiatric symptoms.