Association between TYG-BMI index and asthma in adults over 45 years of age: analysis of Global Burden of Disease 2021, China Health and Retirement Longitudinal Study, and National Health and Nutrition Examination Survey data

BACKGROUND: Asthma remains a major global health burden, particularly in adults aged ≥45 years. The relationship between the composite triglyceride-glucose-body-mass-index (TYG-BMI) and asthma risk in this age group has not been defined. METHODS: This cross-sectional study integrated data from the Global Burden of Disease (GBD) 2021 study, the China Health and Retirement Longitudinal Study (CHARLS), and the National Health and Nutrition Examination Survey (NHANES). After exclusions, 9,432 participants from CHARLS and 1340 from NHANES were included. The TYG-BMI index was calculated and participants were divided into quartiles. Restricted cubic spline (RCS) and segmented regression models were used to analyze the relationship between TYG-BMI and asthma risk. RESULTS: The GBD 2021 data shows high BMI is the top risk factor for asthma-related DALYs globally. CHARLS and NHANES studies both find a nonlinear relationship between TYG-BMI and asthma risk, with critical points at 199.51 and 246.905, respectively. Below the threshold, asthma risk decreases (OR = 0.985, 95% CI: 0.978-0.991 in CHARLS); above it, risk increases (OR = 1.0003, 95% CI: 1.0000-1.0005 in CHARLS; OR = 1.004, 95% CI: 1.001-1.009 in NHANES). A 10-unit increase above the threshold raises asthma risk by 0.3-4%, while a 10-unit decrease reduces it by 14%. This underscores the preventive value of optimizing metabolic status. CONCLUSION: This study provides the large-scale evidence of a nonlinear relationship between the TYG-BMI index and asthma risk in individuals aged 45 and older.