Metabolic health, independent of body mass index, is associated with mortality risk in type 1 diabetes.

AIMS/INTRODUCTION: Although a low body mass index (BMI) is traditionally associated with high mortality in type 1 diabetes (T1D), the increasing prevalence of obesity and its association with mortality warrant further research. MATERIALS AND METHODS: Using a nationwide Korean database from 2002 to 2018, we classified patients with T1D into six categories based on metabolic health and BMI (≥25, 18.5-25, and <18.5 kg/m2): metabolically healthy obesity (MHO), metabolically unhealthy obesity (MUO), metabolically healthy normal weight (MHNW), metabolically unhealthy normal weight (MUNW), metabolically healthy underweight (MHUW), and metabolically unhealthy underweight (MUUW). Mortality data were collected until 2020. RESULTS: Among 8,838 patients with T1D (mean age 54.7 years, 60.6% male), the prevalence of MUUW, MHUW, MUNW, MHNW, MHO, and MUO was 1.1%, 3.0%, 28.5%, 31.2%, 6.3%, and 29.9%, respectively. Over a median 8.3-year follow-up, patients with MHO exhibited the lowest all-cause mortality risk (adjusted hazard ratio [aHR], 0.70; P = 0.007), and those with MUO also had a lower risk (aHR, 0.77; P < 0.001) compared with the MHNW group. Conversely, the underweight groups had significantly higher all-cause (MHUW: aHR, 2.08; MUUW: aHR, 3.94) and cardiovascular disease (CVD)-related mortalities (MHUW: aHR, 2.47; MUUW: aHR, 6.31). Patients with MHO had a lower risk of CVD (aHR, 0.76), whereas those with MUO, MUNW, and MUUW had increased risks (aHRs, 1.18, 1.32, and 2.22). CONCLUSIONS: Metabolic unhealthiness was associated with a higher CVD risk, and the risks of mortality and CVD were particularly high in patients with MUUW, underscoring the importance of maintaining metabolic health in T1D.