Digital Health Management for Night Shift Workers

INTERVENTION: Behavioral : The intervention is a 12‐week wearable and remote‐coaching program grounded in Self‐Determination Theory (SDT), comprising four components. ? Wearable: participants in the intervention group wear a consumer smartwatch (Garmin Vivoactive 5) continuously for 12 weeks, which automatically records physical activity, sleep, and heart rate for self‐monitoring through the linked app. ? Automated tailored messages: messages are generated from the participant's own wearable data and shift schedule and are written in an autonomy‐supportive tone that offers choice, information, and acknowledgment rather than directives, covering physical activity, sleep hygiene, and eating during night shifts. ? Eight remote coaching sessions based on motivational interviewing (MI): sessions are weekly during weeks 1‐4 (sessions 1‐4) and biweekly at weeks 6, 8, 10, and 12 (sessions 5‐8), reflecting the early habit‐formation period. Each session lasts 15‐20 minutes and is delivered by messenger or telephone. Sessions follow a five‐stage autonomy‐supportive structure (engaging, informing, exploring, planning, closing) and use open questions, reflections, and summaries so that participants set their own goals and action plans. A standard session guide and session‐by‐session fidelity checks are used for quality control, and coaching is delivered by an unblinded intervention researcher. ? Sleep and circadian management module: shift‐worker sleep hygiene information on post‐shift light exposure, sleep environment, and caffeine timing. [Between‐Group Differences] The control group receives the same educational materials as the intervention group and undergoes two post‐health‐examination follow‐up counseling sessions at weeks 1 and 3. These sessions are limited to explaining examination results and providing routine follow‐up care, and do not include coaching elements such as goal setting, action planning, autonomy support, or motivational interviewing, nor wearable devices or automated tailored messages. Accordingly, the difference between the two groups lies not in the amount of intervention but in the presence or absence of the program's distinctive components (wearable‐based self‐monitoring, autonomy‐supportive tailored messages, MI coaching, and the sleep–circadian module). To ensure equity after study completion, a condensed delayed intervention consisting of two sessions will be offered to control group participants who provide separate consent; this will not be included in the efficacy analysis. [Blinding] Owing to the nature of the intervention, participants and the coaching researcher are necessarily aware of allocation (open label); however, outcome assessors and the statistician remain blinded to group assignment, reducing bias at the measurement and analysis stages. CONDITION: Endocrine, nutritional and metabolic diseases PRIMARY OUTCOME: Waist circumference (cm), measured with a tape at the midpoint between the lowest rib and the iliac crest per WHO guidelines; the mean of two repeated measurements taken by the same blinded assessor is used. Between‐group differences are analyzed with adjustment for baseline values. INCLUSION CRITERIA: 1. Workers aged 19 years or older who undergo special health examinations for night shift work 2. Presence of at least one metabolic risk factor (including those under pharmacological treatment for each condition): ‐ Abdominal obesity/obesity: waist circumference 90 cm or more in men, 85 cm or more in women, or body mass inde X25 kg/m2 or more ‐ Hypertension: 130/85 mmHg or higher ‐ Impaired fasting glucose: fasting glucose 100 mg/dL or higher ‐ Dyslipidemia: triglycerides 150 mg/dL or higher, HDL cholesterol below 40 mg/dL in men or below 50 mg/dL in women, or LDL cholesterol 130 mg/dL or higher 3. Expected to remain employed at the workplace throughout the study period (approximately 3‐4 months) 4. Able to use a smartphone and provides written informed consent SECONDARY OUTCOME: Acceptability and usability of the intervention: satisfaction, System Usability Scale (SUS), and Theoretical Framework of Acceptability (TFA); measured in the intervention group only Agreement between wearable sleep estimates and a shift‐worker sleep diary: total sleep time, sleep efficiency, sleep onset latency, and wake after sleep onset; assessed in the control group after study completion Depressive symptoms: Patient Health Questionnaire‐9 (PHQ‐9) Metabolic risk indicators: systolic and diastolic blood pressure (mmHg), body mass inde X(kg/m2), fasting glucose (mg/dL), total cholesterol, triglycerides, HDL cholesterol, and LDL cholesterol (mg/dL) Self‐Determination Theory mediators: basic psychological need satisfaction (BPNSFS), autonomous motivation (TSRQ), perceived competence (PCS), and perceived autonomy support (HCCQ) Subjective sleep outcomes: Insomnia Severity Index, Korean version (ISI‐K) and Pittsburgh Sleep Quality Index, Korean version (PSQI‐K) Wearable‐derived physical activity and sleep indices, and night‐work burden indices derived from shift records (frequency, consecutive nights, cumulative exposure); exploratory outcomes