Ehrmann, DominicDominicEhrmann0000-0002-5794-5596Ruch, BernhardBernhardRuchMitter, MichaelMichaelMitterKober, JohannaJohannaKoberHermanns, NorbertNorbertHermanns0000-0002-2903-2677Schäfer, VanessaVanessaSchäferKulzer, BernhardBernhardKulzerSilbermann, StephanStephanSilbermann2026-08-112026-08-1120251438-8871https://fis.uni-bamberg.de/handle/uniba/116737Background: The treatment of diabetes requires substantial self-management. Digital tools can help reduce the burden of self-management and may improve glycemic control. Objective: This study aims to determine whether the use of a digital diabetes logbook increased the likelihood of achieving optimal glycemic control (glycated hemoglobin [HbA1c] ≤6.5%) after 3 months, based on a secondary analysis of randomized controlled trial (RCT) data. A secondary objective was to evaluate the long-term impact of the logbook on mean blood glucose levels over 3 and 12 months using observational, real-world data (RWD). Methods: Data from 342 participants with type 1 or type 2 diabetes enrolled in the mySugr PRO-RCT were analyzed. A robust logistic regression was performed to examine the likelihood of achieving optimal glycemic control, defined as an HbA1c value ≤6.5% at the 3-month follow-up. The dependent variable was the dichotomous outcome indicating whether this threshold was met. The primary independent variable was group allocation, with baseline HbA1c included as a covariate. For the analysis of RWD, a total of 2861 participants with type 1 or type 2 diabetes were identified using propensity score matching to align their characteristics with those of the RCT participants closely. One-sample t tests were conducted to analyze changes in mean blood glucose separately for each diabetes type, from baseline to 3 months of app use, and from baseline to 12 months of app use (in a subcohort of 1176 participants). Results: The RCT data showed that the likelihood of achieving optimal glycemic control was nearly doubled in the intervention group compared with the control group (odds ratio 2.24, 95% CI 1.12-4.47; P=.02). RWD indicated that mean blood glucose levels significantly improved over 3 months of app use in both groups (type 1: –16.3 mg/dL; 95% CI –20.6 to –12.4; P<.001 and type 2: –27.3 mg/dL, 95% CI –28.7 to –25.9; P<.001). Participants with an estimated HbA1c>8.5% at baseline (before app use) showed the greatest reductions in mean blood glucose (type 1: –82.2 mg/dL; 95% CI –102.0 to –61.8; P<.001; type 2: –104.6 mg/dL, 95% CI –109.1 to –100.3; P<.001). Long-term analyses revealed a sustained reduction in mean blood glucose over a 12-month period, with a mean decrease of –19.8 mg/dL (95% CI –21.8 to –17.9; P<.001) after 12 months of app use in the total RWD sample. Conclusions: The secondary analysis of the RCT demonstrated a significant increase in the likelihood of achieving optimal glycemic control after 3 months of using the mySugr logbook. This finding was supported by observational, real-world data, which showed significant reductions in mean blood glucose after 3 and 12 months of app use—particularly among individuals with elevated baseline HbA1c levels. Trial Registration: German Clinical Trials Register DRKS00022923; https://drks.de/search/en/trial/DRKS00022923/detailsengrandomized controlled trialreal-world dataglycemic controldigital health apptype 1 diabetestype 2 diabetesarticle10.2196/68933