Association between Weight-adjusted Waist Index and Pulmonary Function: A Population-Based Study from the NHANES (2007–2012)

Background: The relationship between central obesity and pulmonary function remains a critical area of investigation. The Weight-Adjusted Waist Index (WWI) has emerged as a novel marker for assessing central obesity. This study aimed to investigate the association between WWI and various pulmonary function indices. Methods: Data were extracted from the National Health and Nutrition Examination Survey (NHANES) 2007–2012, involving 8,361 participants. Participants were categorized into tertiles based on their WWI values. Pulmonary function measures included Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV1), FEV1/FVC ratio, and Peak Expiratory Flow rate at 25–75% of forced vital capacity (PEF25–75%). Multivariate linear regression models were used to assess associations, adjusting for covariates such as gender, age, race, education level, hypertension, diabetes, smoking status, and poverty index ratio. Results: Higher WWI was significantly associated with lower FVC, FEV1, and PEF25–75%, but not with FEV1/FVC ratio. Specifically, each unit increase in WWI corresponded to reductions in FVC (-603.9 ml, 95% CI: -628.7, -579.2), FEV1 (-527.7 ml, 95% CI: -547.7, -507.7), and PEF25–75% (-550.5 ml/s, 95% CI: -581.7, -519.3). Sensitivity analyses confirmed these findings after adjusting for multiple covariates. Subgroup analyses indicated similar trends across different genders and age groups. Conclusion: The Weight-Adjusted Waist Index (WWI) is negatively associated with lung volumes and mid-expiratory flow rates, suggesting its potential role in respiratory impairment. These results underscore the importance of considering central adiposity in clinical evaluations of pulmonary health. Future longitudinal studies are warranted to further elucidate the mechanisms underlying these associations and to validate these findings in diverse populations.