U-shaped association between body roundness index and PEF%-defined airflow limitation among middle-aged and older adults in CHARLS: a cross-sectional study

Although central adiposity has been linked to impaired lung function, evidence relating body roundness index (BRI) to airflow limitation defined by percentage of predicted peak expiratory flow (PEF%) in Chinese adults remains limited. PEF% was calculated as the ratio of measured to predicted PEF. We analyzed 15,573 participants aged 45 years or older from the 2015 China Health and Retirement Longitudinal Study (CHARLS). Airflow limitation (AL) and severe airflow limitation (SAL) were defined as PEF% < 80% and PEF% < 60%, respectively. Multivariable logistic regression with sequential adjustment was used. Nonlinearity was assessed using restricted cubic splines (RCS), and the RCS-derived nadir was subsequently used as a fixed knot in segmented logistic regression; effect modification and robustness were assessed in interaction and sensitivity analyses. Following adjustment for potential confounders, in the continuous analyses, RCS analyses indicated U-shaped associations of BRI with AL and SAL (both P for nonlinearity < 0.001), with both spline curves reaching their lowest point at approximately BRI = 4.9. Below 4.9, each 1-unit increase in BRI was associated with approximately 14% lower odds of both outcomes; at or above 4.9, the corresponding increases in odds were approximately 9% and 10% for AL and SAL, respectively. In quartile analyses, participants in Q2–Q4 had lower odds of AL and SAL than those in Q1; the odds ratios (ORs) were essentially unchanged across Q2–Q4 for AL and showed modest variation without a progressive increase toward Q4 for SAL. Significant interactions were observed for age, sex, and smoking status for AL and for sex and smoking status for SAL. The findings remained robust in sensitivity analyses. In Chinese adults aged ≥ 45 years, continuous analyses showed U-shaped associations of BRI with PEF%-defined AL and SAL, with the fitted curves reaching their lowest point at approximately BRI = 4.9.