Prolonged Sedentary Bouts Predict Adverse Glycemic Outcomes Over 12 Months in Adults with Type 2 Diabetes: A Smartphone-Based Prospective Cohort Study

Background: Lifestyle behaviours such as physical activity, sedentary time and sleep play a central role in the management of Type 2 diabetes. Advances in smartphone technology now allow continuous, real-world monitoring of these behaviours at scale. While overall physical activity has a well-established relationship with glycemic control, less is known how the patterning of sedentary behaviour, sleep regularity and routine postmeal walking influence long-term glycemic outcomes and cardiometabolic risk. Objectives: To evaluate whether smartphone-derived sedentary bout length, daily step count, post-meal steps, and regularity predict 12-month change in HbA1c and incident metabolic syndrome among overweight and obese adults. Methods: We conducted a 12 months observational cohort study of 252 adults (18-60 years) with type 2 diabetes using smartphone-based activity and sleep tracking. Average Sedentary bout length (minutes), daily steps, post-meal steps and sleep regulatory score were derived from passively collected smartphone data. Clinical measurements included baseline and 12-month HbA1c and 12 month metabolic syndrome status. Sleep regularity was assessed using the Sleep Regularity Questionnaire (SRQ). For Aim 1, we fit a multivariable linear regression with 12-month HbA1c change as outcome and sedentary bout length as primary predictor, adjusted for age, sex, BMI, baseline HbA1c, and daily steps. For Aims 2 and 3, we used multivariable logistic regression models with incident metabolic syndrome at 12 months as outcome and sleep regularity (Aim 2) or post-meal steps (Aim 3) as primary predictor, adjusting for age, sex, BMI, baseline HbA1c, and daily steps. Results: Longer sedentary periods were independently linked to less favorable HbA1c changes. Each extra minute in average sedentary bout length was associated with about 0.002 percentage point higher HbA1c over 12 months (β) 0,0021, 95% CI roughly 0.001-0.003, p < 0.001) after adjustment. This means a 0.06 percentage point increase in HbA1c over 12 months for a 30-minute difference in sedentary bout length. In contrast, sleep regularity score was not significantly connected with incident metabolic syndrome at 12 months in adjusted logistic regression (odds ratio near 1.0, 95 % CI including 1). Similarly, post-meal steps showed no statistically significant protective link with incident metabolic syndrome after adjustment. Conclusions: In this smartphone-based cohort of adults with diabetes, longer sedentary bouts, independent of total daily steps, predicted worse 12-month HbA1c trajectories. Sleep regularity and post-meal stepping were not clearly associated with incident metabolic syndrome, though limited power and measurement error may have influenced results. Targeting interruptions in sedentary periods could be a practical focus for digital health interventions aimed at improving glycemic control control.