Differential association of body mass index on glycemic control in type 1 diabetes

Background: In contrast to type 2 diabetes, the association of body mass index (BMI) with glycemic control in type 1 diabetes (T1D) remains unclear. We investigated the relationship between BMI and average HbA_1c levels in subjects with T1D. Method: In this multi-centre observational study, we analysed 719 subjects with T1D aged ≥18 years. Average HbA_1c levels over 18 months and other clinical and laboratory parameters were evaluated. Results: The mean age and duration of diabetes at baseline were 41.5 ± 13.9 and 11.3 ± 8.7 years, respectively. A U-shaped correlation between BMI and 18-month average HbA_1c levels was documented by a spline curve. Based on this finding, subjects were divided into three groups according to BMI (group I, <21; group II, 21–23; and group III, ≥23 kg/m²). In group I, the BMI negatively correlated with average HbA_1c (r = −0.172, p = 0.011), while a positive relationship was observed (r = 0.162, p = 0.012) in group III. Average HbA_1c levels were lower and the proportion of individuals with well-controlled glycemia (HbA_1c <7%) were increased in the higher BMI tertile group among subjects with group I as well as in the lower BMI tertile group among subjects with group III BMI. After adjustment with additional covariates in the multiple regression model, these associations between BMI and HbA_1c levels according to the different BMI ranges remained significant. Conclusions: In Korean subjects with T1D, an inverse relationship of BMI with HbA_1c levels was observed in the low BMI group, while a positive correlation was shown in the high BMI group.