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/m2 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.