CIRCADIAN PHASE AND FUNCTION IN YOUNG INDIVIDUALS WITH DEPRESSIVE SYMPTOMS

Circadian desynchronization has been consistently associated with depression. However, the nature of circadian disruptions underlying this disorder remains unclear. This study aimed to identify the association of two fundamental aspects of circadian rhythms (phase and function) with depressive symptoms by using different subjective and objective instruments. Fifty-one young individuals (18–34 years) with depressive symptoms (n=22) and controls (n=29) participated in this study. Participants completed self-report questionnaires for estimating circadian preferences (MEQ) and chronotype (MCTQ). Actigraphy data were used to measure circadian phase proxies (M10c, L5c, acrophase) and the circadian function index (CFI, integrating interdaily stability (IS), intradaily variability (IV), and relative amplitude (RA)). Peripheral temperature was continuously recorded during one-night bedtime. Dim-light melatonin onset (DLMO) was assessed by hourly salivary sampling (18:00-24:00) Participants with depressive symptoms exhibited later indexes of circadian phase than controls measured by MEQ (p=0.006), MCTQ (p=0.01), acrophase (p=0.01), and M10c (p=0.05), but not by L5c, DLMO, and temperature nadir. Regarding circadian function, participants with depressive symptoms exhibited lower RA (p=0.009) but no significant changes in IV compared with controls. Chronotype emerged as the strongest predictor of depressive symptom severity. Cluster analysis identified two subgroups characterized by distinct circadian phase and rest–activity rhythm profiles. These findings provide further insight into the association between the circadian system and depression in young individuals, underscoring the relevance of circadian rhythm integrity in mental health.