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

This single-site prospective observational study aims to validate wearable-derived circadian and behavioral rhythm biomarkers using continuous core body temperature and raw accelerometry measurements and to explore longitudinal changes in circadian and rest-activity rhythms in psychiatric inpatients. The study consists of two complementary substudies. Study 1 will enroll 150 outpatients and community participants, including 75 patients with major depressive disorder or bipolar I/II disorder and 75 healthy controls. Participants will simultaneously wear a CALERAResearch core body temperature sensor and a Fitbit Charge 6 for approximately 7 days. Agreement between Fitbit-derived circadian and sleep/activity rhythm features and CALERAResearch-derived core body temperature and raw accelerometry markers will be evaluated. A subset of 50 participants will undergo a second measurement at least 1 month later to assess test-retest reliability. Study 2 will enroll 50 psychiatric inpatients irrespective of final diagnosis. Participants will continuously wear CALERAResearch and Fitbit devices from shortly after admission through the inpatient observation period, with CALERAResearch sensors replaced approximately every 5-7 days. Longitudinal changes in core body temperature rhythms, rest-activity rhythms, and physiological-behavioral rhythm alignment will be examined in relation to changes in psychiatric symptoms.

Inclusion Criteria Study 1 - Outpatient mood disorder group 1. Adults aged 19-75 years. 2. Meets DSM-5 criteria for major depressive disorder, bipolar I disorder, or bipolar II disorder based on a structured diagnostic interview and clinical assessment, with a history of psychiatric consultation for related symptoms. 3. Agrees to wear both the core body temperature sensor and wrist-worn wearable device for approximately 7 days. Study 1 - Healthy control group 1. Adults aged 19-75 years. 2. Has no history of psychiatric diagnosis or treatment and is not identified as having a major mood disorder on structured diagnostic assessment. 3. Agrees to wear both the core body temperature sensor and wrist-worn wearable device for approximately 7 days. Study 2 - Psychiatric inpatient group 1. Adults aged 19-75 years. 2. Admitted to the psychiatric inpatient unit of Korea University Anam Hospital for psychiatric treatment; a confirmed final diagnosis is not required at enrollment. 3. Agrees to continuously wear the core body temperature sensor and Fitbit during the inpatient study period. Exclusion Criteria Study 1 - Outpatient mood disorder group 1. History of moderate or severe intellectual disability. 2. Current or previous head trauma associated with loss of consciousness, degenerative neurological disease, or organic neurological disorder. 3. Shift work, including night work, within the preceding 3 months. 4. Travel across three or more time zones within the preceding 2 weeks. 5. Fever (body temperature ≥37.5°C) or acute infection at the start of measurement. 6. Pregnancy or breastfeeding. 7. Skin disease at the sensor attachment site, history of allergy to medical adhesives, or another condition making sensor attachment inappropriate. 8. Difficulty reading or understanding Korean. 9. Considered unsuitable for study participation by the principal investigator. Study 1 - Healthy control group 1. History of clinically significant mood symptoms, defined as previous diagnosis or treatment for a mood disorder or evidence of a past or current major depressive, manic, or hypomanic episode on structured or screening assessment. 2. Current use of sleep medications or psychotropic medications, including antidepressants, mood stabilizers, antipsychotics, or benzodiazepines. 3. History of moderate or severe intellectual disability. 4. Current or previous head trauma associated with loss of consciousness, degenerative neurological disease, or organic neurological disorder. 5. Shift work, including night work, within the preceding 3 months. 6. Travel across three or more time zones within the preceding 2 weeks. 7. Fever (body temperature ≥37.5°C) or acute infection at the start of measurement. 8. Pregnancy or breastfeeding. 9. Skin disease at the sensor attachment site, history of allergy to medical adhesives, or another condition making sensor attachment inappropriate. 10. Difficulty reading or understanding Korean. Study 2 - Psychiatric inpatient group 1. An acute safety concern, including risk of harm to self or others, that makes wearable monitoring or study assessment inappropriate. 2. Lack of capacity to provide informed consent or difficulty providing voluntary informed consent. 3. History of moderate or severe intellectual disability. 4. Current or previous head trauma associated with loss of consciousness, degenerative neurological disease, or organic neurological disorder. 5. Fever (body temperature ≥37.5°C) or acute infection at the start of measurement. 6. Pregnancy or breastfeeding. 7. Skin disease or history of allergy to medical adhesives that makes sensor attachment inappropriate. 8. Difficulty reading or understanding Korean.