Postexercise Glycemic Control in Type 1 Diabetes Is Associated With Residual β-Cell Function

OBJECTIVE: To investigate the impact of residual β-cell function on continuous glucose monitoring (CGM) outcomes following acute exercise in people with type 1 diabetes (T1D). RESEARCH DESIGN AND METHODS: Thirty participants with T1D for ≥3 years were recruited. First, participants wore a blinded CGM unit for 7 days of free-living data capture. Second, a 3-h mixed-meal test assessed stimulated C-peptide and glucagon. Peak C-peptide was used to allocate participants into undetectable (Cpep(und) <3 pmol/L), low (Cpep(low) 3–200 pmol/L), or high (Cpep(high) >200 pmol/L) C-peptide groups. Finally, participants completed 45 min of incline treadmill walking at 60% VO(2peak) followed by a further 48-h CGM capture. RESULTS: CGM parameters were comparable across groups during the free-living observation week. In the 12- and 24-h postexercise periods (12 h and 24 h), the Cpep(high) group had a significantly greater amount of time spent with glucose 3.9–10 mmol/L (12 h, 73.5 ± 27.6%; 24 h, 76.3 ± 19.2%) compared with Cpep(low) (12 h, 43.6 ± 26.1%, P = 0.027; 24 h, 52.3 ± 25.0%, P = 0.067) or Cpep(und) (12 h, 40.6 ± 17.0%, P = 0.010; 24 h, 51.3 ± 22.3%, P = 0.041). Time spent in hyperglycemia (12 h and 24 h glucose >10 and >13.9 mmol/L, P < 0.05) and glycemic variability (12 h and 24 h SD, P < 0.01) were significantly lower in the Cpep(high) group compared with Cpep(und) and Cpep(low). Change in CGM outcomes from pre-exercise to 24-h postexercise was divergent: Cpep(und) and Cpep(low) experienced worsening (glucose 3.9–10 mmol/L: −9.1% and −16.2%, respectively), with Cpep(high) experiencing improvement (+12.1%) (P = 0.017). CONCLUSIONS: Residual β-cell function may partially explain the interindividual variation in the acute glycemic benefits of exercise in individuals with T1D. Quantifying C-peptide could aid in providing personalized and targeted support for exercising patients.