The influence of Circadian Rhythm on Mood Disorders

Mood disorders are among the leading causes of disability; their etiology is recognized to involve chronobiological dysregulation. The circadian system, governed by a central pacemaker in the suprachiasmatic nucleus (SCN), orchestrates daily rhythms in sleep, hormone secretion, and neurotransmission. Circadian rhythm disruption plays a central role in the onset and maintenance of mood disorders, including major depressive disorder (MDD), bipolar disorder (BD), seasonal affective disorder (SAD), and anxiety. Disruption of these rhythms through environmental factors such as light exposure or genetic vulnerabilities can trigger or exacerbate emotional dysregulation. Clinical studies indicate that treatments like bright light therapy, melatonin receptor agonists, and social rhythm therapy are effective in restoring circadian coherence and improving symptoms. This review synthesizes evidence across molecular, endocrine, and behavioral levels, highlighting how disruptions in melatonin and cortisol secretion, sleep-wake cycles, and clock gene expression contribute to the development of psychopathology. It suggests that future directions should emphasize precision approaches based on genetic and circadian biomarkers, aiming to personalize interventions. Moreover, bridging chronobiology with psychiatric care offers promising pathways toward sustainable, rhythm-informed mental health treatments.