Bidirectional relationship between sleep disturbance and depression: Mechanisms, clinical implications, and future directions

Table 1 Phenotypes of sleep disturbance in depressive disorders

Sleep disturbance phenotype	Core clinical features	Common depressive context	Key clinical implications
Insomnia	Difficulty initiating sleep, frequent nocturnal awakenings, early morning awakening with daytime impairment	Major depressive disorder, recurrent depression	Associated with greater symptom severity, poorer treatment response, and increased risk of relapse
Hypersomnia	Prolonged sleep duration, excessive daytime sleepiness, difficulty awakening	Atypical depression, bipolar depression	Suggests circadian and reward system involvement and may inform treatment selection
Circadian rhythm disruption	Delayed or irregular sleep timing, reduced circadian amplitude, increased variability in sleep timing	Unipolar and bipolar depression, shift work related depression	Associated with mood instability and poorer antidepressant response; potential target for chronotherapeutic interventions
Poor sleep quality	Nonrestorative sleep, sleep fragmentation, daytime dysfunction	Across depressive disorders	Linked to persistence of depressive symptoms and functional impairment independent of sleep duration