Central adiposity reflected by the weight-adjusted waist index and spirometric parameters in US children and adolescents

Obesity impairs pulmonary function. This study aimed to investigate the potential relationship between the weight-adjusted waist index (WWI), a novel metric for measuring adiposity, and pulmonary function in children and adolescents. This cross-sectional study used extensive data on WWI and pulmonary function metrics from the 2007 to 2012 National Health and Nutrition Examination Survey. The WWI calculation entails dividing waist circumference (cm) by the square root of weight (kg). Z-scores for each lung function measure were derived from Global Lung Function Initiative references. We employed a weighted multivariate logistic regression model to ascertain the association between lung function and WWI. The application of smooth curve fitting validated the linearity of the relationships. Subgroup analysis and evaluation of interactions were conducted as well. Across all statistical models, no significant association was observed between WWI and forced expiratory volume in 1 second (FEV1) z-score. However, WWI demonstrated a significant positive correlation with forced vital capacity (FVC) z-score. Importantly, a significant negative correlation was consistently found between WWI and FEV1/FVC z-score. In the model with all adjustments, each unit rise in WWI was associated with a decrease of 0.395 in FEV1/FVC z-score (β = -0.395, 95% confidence interval: -0.496, -0.295) and an increase of 0.292 in FVC z-score (β = 0.292, 95% confidence interval: 0.186, 0.398). This study finds a significant negative association between WWI and FEV1/FVC z-score. This highlights the necessity for sustained WWI surveillance to guide public health initiatives.