Association of BMI with mortality and health‐related quality of life among 4.4 million adults: Evidence from a nationwide, population‐based, prospective cohort study

The body mass index (BMI), as an easy-to-calculate measure of body fatness, is closely associated with all-cause mortality, but few studies with a large enough scale have examined the relationship between BMI and quality of life. A comprehensive and precise insight into a new range is needed. Based on the ChinaHEART (Health Evaluation And risk Reduction through nationwide Teamwork), a nationwide, population-based cohort study, 4,485,773 participants living in 20,159 communities or villages were passively followed for death records, through a linkage of data with the National Mortality Surveillance System and Vital Registration. Firstly, we conducted Cox proportional-hazards regression models to assess the hazard ratios (HRs) of BMI on the risk of all-cause and cause-specific mortality. Secondly, we used logistic regression models to examine associations between BMI and health-related quality of life (HRQL). Fully adjusted models were adjusted for age, sex, annual household income, occupation, education level, marriage, medical insurance, urbanity, tobacco smoking, alcohol consumption and the history of hypertension, diabetes mellitus, dyslipidaemia and cardiovascular disease (CVD). Among the 4 485 773 included participants with an average age of 56.4 ± 10.0 years, 59.0% were female. During the follow-up period, which had a median duration of 5.3 years, a total of 142 004 cases of all-cause mortality were confirmed. After adjusting for participant characteristics and lifestyles, we observed the U-shaped association between BMI and all-cause mortality with an inflection of 26-27 kg/m2, and the estimated HR per 1 kg/m2 increase in BMI was 0.92 (95% CI 0.92-0.93) and 1.03 (95% CI 1.03-1.04) below and above the turning point, respectively. An inverted J-shape pattern between BMI and HRQL with a peak of 22-23 kg/m2 was found, in which the odd ratio per 1 kg/m2 increase in BMI was 0.98 (95% CI 0.98, 0.99) below 22-23 kg/m2 and 1.03 (95% CI 1.03-1.03) above this point. We found distinct ranges of BMI for minimized mortality risk and maximized HRQL. The BMI range corresponding to the HRQL is lower than the BMI range corresponding to the lowest risk of death generally. Therefore, it is worth considering how to define the new recommended range for a new BMI based on the goal of 'living a longer and healthier life'.