BMI and Lung Function in Asthmatic Children
BMI influences lung performance in children with asthma, with benefits that reverse beyond a critical weight threshold.
Study Overview
Researchers evaluated 328 children experiencing asthma exacerbations to examine how BMI and BMI z-scores correlate with key lung function parameters. Using both linear and piecewise regression analyses, they assessed measures including maximum vital capacity (VCmax), forced vital capacity (FVC), forced expiratory volume in one second (FEV1), peak expiratory flow (PEF), and mid-expiratory flow rates (MEF25, MEF50, MEF75, and MMEF).
Linear and Nonlinear Associations
Both BMI and BMI z-scores were positively associated with several lung function measures, even after adjustment for age, sex, immunoglobulin E, eosinophil count, fractional exhaled nitric oxide, and asthma severity. Children with higher BMI values generally exhibited improved VCmax, FVC, and FEV1.
However, piecewise regression analysis revealed a critical nonlinear threshold between BMI z-scores and lung function. Below a z-score range of approximately 2.3 to 3.9, lung function improved with increasing BMI. Beyond this range, the relationship reversed—higher BMI z-scores were linked to declines in measures such as FEV1 and PEF. Specifically, for each unit increase in BMI z-score above 3.945, FEV1 decreased by 9.7% and PEF by 12.2%.
Clinical Implications
These findings highlight the complex interaction between body weight and pulmonary function in pediatric asthma. While moderate weight gain may support better lung function, excessive weight appears detrimental. Clinicians may consider incorporating weight-guided strategies into asthma management plans to optimize respiratory outcomes.
Reference: Wang J et al. Nonlinear Relationship Between Body Mass Index Z-Scores and Lung Function Parameters in Asthmatic Children: A Cross-Sectional Study. J Asthma Allergy. 2025;18:1455–1465.
