The association between body roundness index and asthma risk in middle-aged and elderly people: a retrospective cohort study based on CHARLS database

The prevalence of asthma is rising globally, posing a significant public health burden. While obesity is a well-established risk factor for asthma, traditional metrics like Body Mass Index (BMI) have limitations in distinguishing visceral adiposity. The Body Roundness Index (BRI) is a novel geometric indicator of central obesity, but its longitudinal association with asthma risk in middle-aged and elderly populations remains unclear. We conducted a retrospective cohort study using data from the China Health and Retirement Longitudinal Study (CHARLS) covering the period from 2011 to 2020. A total of 7,754 participants aged 45 years and older, free of respiratory diseases at baseline, were included. Multivariable Cox proportional hazards models and restricted cubic spline (RCS) analyses were employed to evaluate the association between BRI and the incidence of asthma. During a 7-year follow-up, 521 incident asthma cases were identified. In fully adjusted models, elevated BRI was significantly associated with an increased risk of asthma (Hazard Ratio HR = 1.39, 95% CI: 1.388–1.393 per SD increase). RCS analysis revealed a non-linear U-shaped relationship with a distinct inflection point at a BRI of 4.12. Beyond this threshold, the risk of asthma increased substantially (HR = 1.75, 95% CI: 1.34–2.27). Subgroup analyses demonstrated that the association was more pronounced in females and urban residents. BRI is significantly associated with the risk of asthma in middle-aged and elderly Chinese adults, exhibiting a non-linear dose-response relationship. As a superior marker of visceral adiposity, BRI may serve as a simple and effective tool for identifying high-risk individuals, particularly women, to facilitate early screening and prevention strategies for asthma.