Journal of Medical Internet Research - International Scientific Journal for Medical Research, Information and Communication on the Internet #Preprint #PeerReviewMe: Warning: This is a unreviewed preprint. Readers are warned that the document has not been peer-reviewed by expert/patient reviewers or an academic editor, may contain misleading claims, and is likely to undergo changes before final publication, if accepted, or may have been rejected/withdrawn. Readers with interest and expertise are encouraged to sign up as peer-reviewer, if the paper is within an open peer-review period. Please cite this preprint only for review purposes or for grant applications and CVs (if you are the author). Background: Patient-generated health data or lifelog is becoming an important factor in customized health care as digital health technologies such as personal health record and wearables are advanced. Although utilizing the technologies for a variety of chronic health conditions is reported to be acceptable and useful, there is a lack of evidence of associations between the use of the technologies and the change of health outcome and the sustainable use of digital health application. Objective: We aim at examining the impact of the use of personal health record and wearables on health outcome improvement and sustained use of the health application that can be associated with patient engagement. Methods: We developed an Android-based smartphone application and utilized a wristband-type activity tracker (Samsung Charm) to collect data on health-related daily activities from individual patients. Dietary record, daily step counts, sleep log, subjective stress amount, blood pressure, and weight values were recorded. We conducted a prospective randomized clinical trial across four weeks on those diagnosed with obstructive sleep apnea (OSA) who had visited the outpatient clinic of Seoul National University Bundang Hospital. The trial randomly assigned 60 patients to three subgroups including two intervention groups: 1) mobile app and wearable device users (n = 20), 2) mobile app only users (n = 20), and 3) controls (n = 20). The primary outcome measure was weight change. Body weights before and after the trial were recorded and analyzed during clinic visits. Changes in OSA-related respiratory parameters such as Respiratory Disturbance, Apnea-Hypopnea, and Oxygenation Desaturation indexes and snoring comprised the secondary outcome and were analyzed for each participant. Results: Among 60 participants (40 in two intervention groups and 20 in a control group) who were enrolled, 43 completed the study. We collected the individual data for each group during the trial, specifically, anthropometric measurement and lab test results for health outcomes, and the application usage logs for sustainable use were collected and analyzed. The body weight showed a significant reduction (1.66%) in the two intervention groups after intervention, and the mobile app only group showed more weight loss (2.13%) compared to the controls (0.47%) (P =.01). There were no significant changes in sleep-related health outcomes. For a sustainable use point of view, the average daily step counts (8,165 steps) from the app plus wearable group were significantly higher than those (6,034 steps) from the app only group because they collected step count data from different devices (P =.02). The average rate of data collection was not different in physical activity (49.82% vs 49.96%, P =.99), food intake (32.67% vs 32.82%, P =.98), sleep (32.01% vs 32.45%, P =.95), stress (30.11% vs 27.33%, P =.70) and weight (32.82% vs 31.87%, P =.90) in the app plus wearable and app only groups, respectively. Conclusions: We tried to integrate personal health record data that allows clinicians and patients to share lifelog data with the clinical workflow to support lifestyle interventions. Our results suggest that personal health record-based intervention is successful in losing body weight and improvement in lifestyle behavior. We designed a clinical trial to collect data about physical activity and diet using wearable devices in patients with lifestyle-related diseases and deliver care interventions across four weeks. Our results reveal how patients and clinicians can apply personal health data and mobile applications. Clinical Trial: ClinicalTrials.gov NCT03200223