Optimal body mass index cut-off points for prediction of incident diabetes in a Chinese population.

Background: The current body mass index (BMI) classifications have been established based on the risk of obesity-related conditions, but not specifically on type 2 diabetes mellitus (T2DM). The aim of this study was to identify the optimal BMI cut-off points for assessing incident T2DM risk in the Chinese population.

Methods: The longitudinal study cohort consisted of 8735 non-diabetic participants aged 20-74 years at baseline, with a mean follow-up period of 6.0 years. Body mass index, 2-h plasma glucose after a 75-g oral glucose tolerance test, and HbA1c were measured at baseline and follow-up.

Results: During the follow-up period, 825 participants were diagnosed with T2DM. In multivariable Cox regression analyses, after adjusting for covariates, a strong positive association between BMI and incident T2DM was found in the whole population; however, when stratified by age groups (20-39, 40-59, and 60-74 years), the risk associations between BMI and incident T2DM decreased with increasing age and were no longer evident in the 60-74 years group (P  < 0.001). The optimal BMI cut-off points for predicting T2DM risk for men and women were 25.5 and 24.4 kg/m , respectively, in the 20-39 years group, and 23.5 and 23.0 kg/m , respectively, in the 40-59 years group. There was no predictive performance of BMI in the 60-74 years group for either sex.

Conclusions: The results suggest that the performance of BMI in predicting T2DM risk was best in subjects of younger age and decreased with age. Age- and sex-specific BMI cut-off points should be considered for T2DM risk stratification in the Chinese population.