Body mass index, waist circumference and the association with all-cause and cause-specific mortality: a 7.2-year follow-up cohort study in Shanghai, China

Abstract

Objective: Studies on the effects of obesity on mortality have contradictory findings, and few studies have focused on the relationship between the combined effect of body mass index (BMI) and waist circumference (WC) and the range of specific causes of death. We aimed to investigate the association between BMI, WC, or both and all-cause and cause-specific mortality among adults in China. Methods: This prospective cohort study was performed in Songjiang District, Shanghai, and included 35,787 participants aged 20–74 years. Questionnaire interviews, anthropometric measurements, and laboratory assays were conducted to collect baseline data. BMI (kg/m2) was categorized as follows: underweight (< 18.5), normal weight (18.5–23.9), overweight (24.0–27.9), grade 1 obesity (28.0–31.9), grade 2 obesity (32.0–35.9), and grade 3 obesity (≥ 36.0). WC was categorized into central obesity and non-central obesity. Cox regression models were used to analyze the relationship between BMI and WC and the risk of mortality. Results: During a median of 7.16 years of follow-up, 1250 deaths were recorded. Underweight was negatively associated with mortality. A BMI in the range of 24.0–31.9 kg/m2 was a protective factor for all-cause and cardiovascular disease (CVD) mortality, while central obesity was related to a high mortality risk. The joint effect of a high BMI and a normal WC presented lower all-cause (HR: 0.79, 95%CI: 0.68–0.91) and CVD mortality (HR: 0.67, 95%CI: 0.49–0.92). The restricted cubic spline showed a U-shaped association between BMI and overall (lowest mortality risk at 27.4 kg/m2) and CVD mortality (lowest mortality risk at 27.5 kg/m2), as well as a J-shaped association between WC and mortality. Conclusion: Maintaining a relatively high BMI of 24.0–27.9 kg/m2 and a normal WC can reduce the risk of overall and CVD mortality. The U-shaped association between BMI and mortality also suggests that both underweight and extremely high BMI should be avoided.