Trajectory of body mass index before the development of type 2 diabetes in Japanese men: Toranomon Hospital Health Management Center Study 15

AIMS/INTRODUCTION: We aimed to investigate the long-term trajectory of general adiposity assessed by the body mass index (BMI) before the onset of type 2 diabetes in Japanese individuals. MATERIALS AND METHODS: We retrospectively examined data on 1,553 Japanese men without diabetes. Mean BMI and incident cases of diabetes (diabetes indicated by fasting glucose concentrations ≥7.0 mmol/L, a self-reported history of clinician-diagnosed diabetes, or glycated hemoglobin ≥6.5% (≥48 mmol/mol) were assessed on an annual basis over a 10-year period after the baseline examination. RESULTS: Mean (standard deviation) BMI at the time of diagnosis was 24.4 kg/m(2) (3.1 kg/m(2)) among cases of diabetes (n = 191). An increasingly high BMI was associated with the early stage of the disease development, such as an 8- to 10-year prediagnosis period; individuals who developed diabetes experienced a prolonged and stable elevated BMI of ≥24.4 kg/m(2) over the 8 years before the diagnosis of diabetes. The mean BMI among the non-cases of diabetes did not exceed 23.2 kg/m(2) throughout the period. CONCLUSIONS: These results suggested that Japanese men who eventually developed diabetes during the 10-year observation period were not characterized as obese, but had stable high-normal BMIs before the onset of diabetes. Previous evidence showed that values for glycemic markers rapidly increased before the development of diabetes; however, the present study showed a slight gain in BMI in the earlier stage of the natural history of diabetes followed by a prolonged period of overweight.