Body mass index and the all-cause mortality rate in patients with type 2 diabetes mellitus

Aims - The relationship between obesity and mortality rate among diabetic patients is a controversial topic. The aim of this study was to investigate the association between obesity and all-cause mortality risk in patients with type 2 diabetes. Methods - In this retrospective database study, 2383 patients with type 2 diabetes, who had been registered in the Isfahan Endocrine and Metabolism Research Center, Iran, were enrolled between 1992 and 2010. The mean (SD) of diabetes duration and follow-up period was 15.5 (8.0) and 7.8 (3.9) years. The main outcome was all-cause mortality. All-cause mortality rates were calculated for the body mass index (BMI) categories of underweight, normal, overweight and class I, II and III obese. Cox proportional hazard models were used to estimate the adjusted hazard ratio for BMI as categorical variable using BMI of 18.5–24.9 kg/m2 as the reference group. Results - The mortality rate in patients with normal weight was higher than overweight patients (59.11 vs. 33.17 per 1000 person-years). The adjusted hazard ratios of all-cause mortality were 0.82 [95%CI 0.68–0.99; P = 0.037], 0.79 [95%CI 0.61–1.02; P = 0.069], 0.71 [95%CI 0.42–1.19; P = 0.191] and 1.36 [95%CI 0.55–3.33; P = 0.507] for overweight, class I, II and III obesity, respectively. When BMI was included in the Cox model as a time-dependent variable, the U-shaped relationship between BMI and all-cause mortality did not change. Conclusions - The results show a U-shaped association of BMI with all-cause mortality in patients with type 2 diabetes with the lowest risk observed among the overweight patients.