To investigate the association of obesity and all-cause mortality in a sample of middle-aged and elderly population.

Information of participants was collected in the Dongfeng-Tongji study, a perspective cohort study of Chinese occupational population. The main outcome was risk of death after 8.5 years of follow-up.

We examined the association of BMI, waist circumference (WC, and waist–height ratio (WHtR) with all-cause mortality in the Dongfeng-Tongji cohort study (n=26,143). Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CI) for all-cause mortality. Area under the receiver operating characteristic curves and net reclassification improvement (NRI) were used to calculate the power of prediction models.

During a mean of 8.5 years of follow-up, 2,246 deaths were identified. There is a U-shaped association of BMI with all-cause mortality in the middle-aged and elderly Chinese population. Compared with individuals with normal BMI, underweight was positively (HR=2.16, 95% CI: 1.73, 2.69) while overweight (HR=0.75, 95% CI: 0.67, 0.84) and obesity (HR=0.67, 95% CI: 0.56, 0.79) were negatively associated with all-cause mortality after adjustment for potential confounders including WC. In contrast, WC (Q5 vs. Q1, HR=1.55, 95% CI: 1.29, 1.86) and WHtR (Q5 vs.Q1, HR=1.69, 95% CI: 1.40, 2.04) were positively associated with mortality after further adjustment for BMI (P trend < 0.001). Addition of both BMI and WC into the all-cause mortality predictive model significantly increased AUC (P =0.0002) and NRI (NRI = 2.57%, P = 0.0007).

BMI and WC/WHtR were independently associated with all-cause mortality after mutual adjustment. Combination of BMI and WC/WHtR improved the predictive ability of all-cause mortality risk in the middle-aged and elderly population.