김성재 Seong Jae Kim
DOI:
Abstract
Circadian rhythms are endogenous near-24-hour oscillations that regulate sleep- wake behavior, activity, hormone secretion, body temperature, cognition, and mood. Depression is associated not only with affective dysregulation but also with disturbances in biological timing. Patients with depression frequently show abnormalities in sleep-wake rhythm, evening chronotype, rest-activity rhythm, melatonin and cortisol rhythms, and seasonal mood variation. Recent studies support these findings, showing sleep fragmentation, reduced amplitude in rest- activity rhythm, and altered hormonal rhythms in depression. These findings suggest that circadian misalignment may contribute to depressive symptoms by disturbing sleep recovery, neuroendocrine regulation, and emotional stability.
This review discusses depression from the perspective of circadian rhythm dysregulation. Circadian misalignment may function as a physiological stressor, even in the absence of consciously perceived psychological stress. In this context, insomnia, early morning awakening, hypersomnia, daytime fatigue, morning worsening, and seasonal mood changes can be interpreted as clinical clues of disrupted biological timing. Assessment of circadian rhythm in depression may include sleep diaries, chronotype evaluation, actigraphy, light exposure assessment, dim light melatonin onset, and cortisol rhythm measurement. Chronotherapeutic interventions such as bright light therapy, sleep phase advance, wake therapy, melatonin-based treatment, and stabilization of daily routines may complement conventional treatments. A circadian perspective may help refine the pathophysiological understanding of depression and support individualized rhythm-based treatment strategies.
Key Words
Circadian rhythm, Depression, Biological clock, Rest-activity rhythm, Chronotherapy, Light therapy
