Body Mass Index and Mortality Among Japanese Patients With Type 2 Diabetes: Pooled Analysis of the Japan Diabetes Complications Study and the Japanese Elderly Diabetes Intervention Trial

CONTEXT: Previous studies on the association between body mass index (BMI) and mortality in diabetes do not necessarily provide a comprehensive view in terms of the global population because of the exclusion of individuals with a BMI less than 18.5 kg/m(2). OBJECTIVE: The objective of the study was to examine the association between BMI and mortality. DESIGN, SETTING, AND PARTICIPANTS: We analyzed pooled data from 2 cohorts of 2620 Japanese patients with type 2 diabetes followed up for 6.3 years. Patients with a history of cardiovascular disease or cancer were excluded. MAIN OUTCOME MEASURE: The end point was all-cause mortality. Hazard ratios were estimated by Cox regression adjusted for age, smoking, leisure-time physical activity, and other confounders. RESULTS: An analysis using BMI categories of 14.4-18.5 (5.2%), 18.5-22.4 (37.3%), 22.5-24.9 (31.0%), and 25.0-37.5 kg/m(2) (26.6%) revealed no significant trend in mortality among patients with a BMI of 18.5 kg/m(2) or greater (trend P = .69). In contrast, the hazard ratio of patients with a BMI less than 18.5 kg/m(2) vs 22.5-24.9 kg/m(2) was 2.58 (95% confidence interval 1.38-4.84; P < .01). Exclusion of deaths in the first 4 years of follow-up decreased the hazard ratio only slightly. CONCLUSIONS: The lowest mortality rate was observed among patients with a BMI of 18.5-24.9 kg/m(2), and obesity had no benefits regarding mortality. Further research is needed in lean patients, especially among aging populations in East Asia.