Nonlinear Relationship Between Body Mass Index Z-Scores and Lung Function Parameters in Asthmatic Children: A Cross-Sectional Study

Jing Wang,1,2,* Jinmao Gao,3,* Yuling Han,1,2 Lu Cheng,1,2 Xiang Ma1,2 1Department of Respiratory, Jinan Children’s Hospital, Jinan, People’s Republic of China; 2Department of Respiratory, Children’s Hospital Affiliated to Shandong University, Jinan, People’s Republic of China; 3Weifang Detachment of Shandong Provincial Corps, PAP, Weifang, Shandong, People’s Republic of China*These authors contributed equally to this workCorrespondence: Xiang Ma, Children’s Hospital Affiliated to Shandong University, No. 23976, Jingshi Road, Jinan City, Shandong Province, 250022, People’s Republic of China, Email [email protected]: To assess the relationship between body mass index (BMI) and BMI z-scores with lung function parameters in children with asthma, aiming to provide scientific evidence for individualized treatment and management strategies.Methods: We enrolled 328 children with asthma during acute exacerbation. The BMI and BMI z-scores were analyzed in relation to lung function parameters, including maximum vital capacity (VCmax), forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), peak expiratory flow (PEF), maximal mid-expiratory flow rate (MMEF), and instantaneous flows at 25%, 50%, and 75% of maximal expiratory flow (MEF25, MEF50, MEF75). Both linear regression and piecewise regression models were used to identify linear associations and potential threshold effects.Results: BMI showed significant positive linear correlations with VCmax, FVC, FEV1, MEF50, MEF75, and MMEF, while BMI z-scores demonstrated positive linear associations with VCmax, FVC, FEV1, MEF25, MEF50, and MMEF. After adjusting for age, sex, immunoglobulin E (IgE), eosinophil count (EOS), fractional exhaled nitric oxide (FeNO), and asthma severity, both BMI and BMI z-scores remained positively associated with VCmax, FVC, and FEV1. Piecewise regression analysis revealed significant threshold effects in the relationships between BMI z-scores and VCmax, FVC, FEV1, PEF, MEF25, MEF50, MEF75, and MMEF. Below a z-score of ~2.3– 3.9, BMI z-score was positively associated with pulmonary function. Above this threshold, the association reversed; for instance, FEV1 decreased by 9.7% (β = − 9.69, 95% CI: − 18.93 to − 0.46) and PEF decreased by 12.2% (β = − 12.17, 95% CI: − 21.12 to − 3.22) for every unit increase in BMI z-score beyond 3.945.Conclusion: A nonlinear relationship exists between BMI z-scores and lung function parameters in children with asthma. Weight-guided interventions may enhance lung function and asthma control.Keywords: asthma, children, body mass index z-score, lung function, threshold effect