Complicated curve association of body weight at diagnosis with C-peptide in children and adults with new-onset type 1 diabetes.

Aim: To investigate the association of body mass index (BMI) or BMI z-score (BMIz) at diagnosis with β-cell function in new-onset type 1 diabetes (T1D) patients in children and adults.

Methods: This was a retrospective cohort study; 256 children (<18 years) and 245 adults (≥18 years) with less than 1-year duration were recruited and followed for 4 years with an interval of 12 months. Smooth curve fitting, a two-piecewise linear model, and Cox proportional hazards models were utilized to investigate the influence of BMI/BMIz on C-peptide levels.

Results: Heavier patients (BMIz ≥ -1 in children and BMI in adults ≥20.2 kg/m ) had greater C-peptide with a complicated J curve in all age groups after adjustment for age of onset, sex, and disease duration. Moreover, after 4 years of follow-up, patients with higher BMI/BMIz had a lower risk of β-cell failure (HR = 0.7; 95% CI, 0.6-1.0; P = .026). However, no association was found between baseline BMI/BMIz at diagnosis and C-peptide rate of decline during 1 year follow-up.

Conclusion: Association between BMI/BMIz and C-peptide in T1D followed a complicated J curve pattern, and heavier patients had greater C-peptide at diagnosis and a lower risk of β-cell failure at 4 years, suggesting that baseline BMI is a useful predictor for β-cell function in patients with T1D.