Associations of obesity with chronic inflammatory airway diseases and mortality in adults: a population-based investigation

Background The association between obesity and respiratory diseases has been confirmed. However, few studies have reported the relationship between obesity and the risk and mortality of chronic inflammatory airway disease (CIAD). The aim of this study was to reveal the association between obesity and the risk of CIAD, and mortality in patients with CIAD. Methods The study was conducted using data from the National Health and Nutrition Examination Survey (NHANES) 2013 to 2018 among adults aged 20 years and above. All participants were grouped according to body mass index (BMI) and waist circumference (WC) levels to study the relationship between obesity and CIAD. Multivariate logistic regression analysis was utilized to examine the connection between CIAD and obesity in a cross-sectional study. The association between obesity and all-cause mortality in individuals with CIAD was examined using multiple cox regression models and smooth curve fitting in a prospective cohort study. Results When stratified based on BMI in comparison to the normal weight group, the ORs with 95%CIs of CIAD for underweight and obesity were 1.39 (1.01-1.93) and 1.42 (1.27-1.58), respectively. The OR with 95%CI of CIAD for obesity was 1.20 (1.09-1.31) when stratified according to WC. Additionally, underweight was associated with a higher mortality (HR = 2.44, 95% CI = 1.31-4.55), whereas overweight (HR = 0.58,95% CI = 0.39-0.87) and obesity (HR = 0.59,95% CI = 0.4-0.87) were associated with a lower mortality (P for trend < 0.05). There was a non-linear association between BMI and all-cause mortality (P for non-linear = 0.001). An analysis of a segmentation regression model between BMI and all-cause mortality revealed a BMI turning point value of 32.4 kg/m(2). The mortality of CIAD patients was lowest when BMI was 32.4 kg/m(2). When BMI <= 32.4 kg/m(2), BMI was inversely associated with all-cause mortality in patients with CIAD (HR: 0.92, 95%CI:0.88-0.97). However, when BMI > 32.4 kg/m(2), there was no association between BMI and all-cause mortality (HR:1.02, 95%CI:0.97-1.06). Conclusion Compared to normal weight, underweight and obesity were associated with the increased risk of CIAD. Underweight was associated with increased all-cause mortality, while overweight was associated with reduced all-cause mortality. There was a non-linear association between BMI and all-cause mortality in patients with CIAD. The all-cause mortality was lowest when BMI was 32.4 kg/m(2).