Validation of Wearable Core Body Temperature-Based Circadian Rhythm Digital Biomarkers

The study is a single-site prospective observational study conducted at Korea University Anam Hospital and consists of two complementary substudies using wearable core body temperature and wrist-worn sensor data. Study 1 is a validation study designed to evaluate the agreement between circadian and behavioral rhythm features derived from a consumer wrist-worn wearable device (Fitbit Charge 6) and physiological circadian and high-resolution behavioral rhythm markers derived from CALERAResearch. Seventy-five outpatients with DSM-5 major depressive disorder, bipolar I disorder, or bipolar II disorder and 75 healthy control participants will simultaneously wear both devices for approximately 7 days. The primary physiological circadian phase marker is the midpoint of the core body temperature trough. Fitbit-derived circadian phase, sleep, and activity rhythm features will be compared with core body temperature and raw accelerometry-derived measures. A subset of 50 participants will repeat the measurement after an interval of at least 1 month to evaluate test-retest reliability. Study 2 is a transdiagnostic longitudinal observational study of 50 patients admitted to the psychiatric inpatient unit. Eligibility does not depend on a specific final psychiatric diagnosis. Participants will undergo repeated measurement of core body temperature, raw accelerometry, and Fitbit-derived sleep and activity measures from shortly after admission through the inpatient observation period. CALERAResearch sensors will generally be replaced every 5-7 days. Psychiatric symptoms will be repeatedly assessed using the Montgomery-Åsberg Depression Rating Scale, Young Mania Rating Scale, Brief Psychiatric Rating Scale, and Clinical Global Impression. The study will evaluate within-subject changes in circadian and rest-activity rhythms and physiological-behavioral rhythm alignment in relation to changes in psychiatric symptom severity and clinical course. No therapeutic intervention is assigned as part of the study, and no randomization or masking is performed.