24-Hour Movement Behavior Reallocations and Glycemic Variability in Adults With Type 1 Diabetes: A Longitudinal Isotemporal Substitution Analysis

Background: Glycemic variability (GV) is an important cardiometabolic risk marker in adults with type 1 diabetes (T1D). We estimated the effects of reallocating time among sleep, sedentary behavior, light physical activity (LPA), and moderate-to-vigorous physical activity (MVPA) on six GV outcomes in adults with T1D. Methods: This secondary analysis included 23 adults contributing 102 days with concurrent accelerometer-based activity monitoring and continuous glucose monitoring (CGM). Compositional rescaling was applied to ensure a 24-h in total. Isotemporal substitution models with linear mixed-effects regression were used to estimate associations of 30-min reallocations among behaviors (e.g., from sleep to LPA) with GV outcomes, including standard deviation of glucose (SD), coefficient of variation (CV), large amplitude of glycemic excursions (LAGE), mean amplitude of glycemic excursions (MAGE), continuous overlapping net glycemic action with a 60-min lag (CONGA-60), and time in range (TIR), while adjusting for covariates. Results: Participants had a mean age of 32.6 years, BMI of 28.2 kg/m 2 , and diabetes duration of 16.3 years. Reallocating 0.5 hours from sleep to sedentary time, LPA, or MVPA significantly reduced CV (estimate range: −14.4 to −15.2, all p < 0.05) and TIR (estimate range: −3.6 to −3.6, all p < 0.01). Replacing sedentary time with LPA significantly reduced LAGE (estimate = −3.4, p = 0.035). No significant associations were found for SD, MAGE, or CONGA-60. Conclusion: These findings highlight that optimizing glycemic stability in adults with T1D requires a nuanced consideration of how reallocations between sleep, sedentary time, LPA, and MVPA differentially affect GV, TIR, and LAGE.