Incidence of diabetes and its mortality according to body mass index in South Koreans aged 40–79 years

PURPOSE: The purpose of this study was to assess diabetes incidence and all-cause mortality according to baseline body mass index (BMI) and to compare relative risks of mortality associated with incident diabetes across various BMI classes in a cohort of South Korean adults. PATIENTS AND METHODS: Based on data from the National Health Insurance database of Korean individuals aged 40–79 years without preexisting diabetes, we calculated BMI at the baseline health examination. We estimated the relative risk of mortality associated with incident diabetes using time-dependent Cox models and considering the time of diabetes diagnosis. RESULTS: We noted 29,307 incident diabetes cases and 22,940 deaths during an 8-year follow-up of the initial cohort (n=436,692) and 73,756 incident diabetes cases and 57,556 deaths during a 10-year follow-up of the replication cohort (n=850,282). Regarding all-cause mortality, time-dependent Cox models revealed statistically significant interactions between diabetes status and baseline BMI class (P=0.018 and P<0.001 in the initial and replication cohorts, respectively). In separately conducted analyses for each BMI class, diabetes-associated relative risks for BMI values of 16.0–18.4, 18.5–22.9, 23.0–24.9, 25.0–29.9, and 30.0–34.9 kg/m(2) were 1.50 (95% confidence interval [CI], 1.09–2.07), 1.39 (95% CI, 1.26–1.54), 1.20 (95% CI, 1.08–1.35), 1.18 (95% CI, 1.07–1.30), and 0.97 (95% CI, 0.74–1.28) in the initial cohort, and 1.44 (95% CI, 1.18–1.74), 1.33 (95% CI, 1.26–1.41), 1.24 (95% CI, 1.16–1.31), 1.11 (95% CI, 1.05–1.17), and 0.99 (95% CI, 0.85–1.16) in the replication cohort. The increasing trend of relative risk with decreasing BMI persisted mostly among subgroups stratified according to age or sex and smoking status. CONCLUSION: Incident diabetes was associated with a greater increase in all-cause mortality risk in adults with lower BMI relative to those with higher BMI. This emphasizes the importance of treatment and prevention of type 2 diabetes among normal weight or underweight adults, particularly in Asia.