The risk of type 2 diabetes mellitus according to the categories of body mass index: the Korean Genome and Epidemiology Study (KoGES)

Obesity is an established risk factor for type 2 diabetes mellitus (T2DM). However, there is limited information on the pattern of relationship between the risk for T2DM and body mass index (BMI) categories including underweight and overweight. Thus, this study was to evaluate the risk of T2DM according to BMI categories defined by Asian-specific cutoff of BMI. 7660 non-diabetic Koreans were grouped into five BMI categories (underweight, normal, overweight, obese and severe obese) defined by Asian-specific cutoff of BMI and followed up for 10 years to monitor the development of T2DM. With a reference of normal BMI group, Cox proportional hazards assumption was used to calculate hazard ratios (HRs) and their 95% confidence intervals for T2DM in five groups. Subgroup analysis was conducted by gender and age (40-59 years and 60-69 years). Baseline mean value of metabolic factors like fasting glucose, HOMA-IR, total cholesterol and the proportion of impaired fasting glucose increased proportionally to the level of BMI categories. Underweight group had the higher proportion of impaired glucose tolerance than normal and overweight group. In all subgroups, underweight, overweight, obese and severe obese group had the higher HRs for T2DM than normal group, but statistical significance was only found in overweight, obese and severe obese group. The risk of T2DM tends to increase proportionally to the level of BMI categories from overweight to severe obese group. Further studies should be considered to identify the incidental relationship between underweight and T2DM.