The Effects of Asthma on the Association Between Pulmonary Function and Obesity: A 16-Year Longitudinal Study

Background: Asthma and obesity are important public health issues around the world. Obesity is considered a risk factor associated with the severity and incidence of asthma. We investigated the relationships between poor pulmonary function (defined by forced vital capacity (FVC) and percentage of predicted FVC (FVC%)) and obesity. Methods: This is a retrospective longitudinal study using the MJ health examination database in Taiwan from 2000 to 2015. There were 160,609 participants aged >= 20 years with complete obesity indicators and lung function data, and having at least two visits. A generalized estimation equation (GEE) model was applied to estimate the association between lung function and obesity. Results: BMI was the best indicator to predict poor pulmonary function for our participants. Results of BMI are presented as an example: Obesity (body mass index (BMI) >= 27.0 kg/m(2)) is significantly associated with lower FVC [adjusted coefficients (beta) for asthmatics: -0.11 L (95% CI: -0.14, -0.08); adjusted beta for non-asthmatics: -0.08 L (-0.09, -0.08)] and FVC% [adjusted beta for asthmatics: -1.91% (95% CI: -2.64, -1.19); adjusted beta for non-asthmatics: 1.48% (-1.63, -1.33)]. Annual change of BMI (Delta BMI/year) is an independent risk factor for decreased FVC [adjusted beta for asthmatics: -0.030 L (-0.048, -0.013); adjusted beta for non-asthmatics: -0.019 L (-0.022, 0.016)] and FVC% [adjusted beta for non-asthmatics: -0.603% (-1.063, -0.142); adjusted beta for nonasthmatics: -0.304% (-0.393, -0.214)], and is significantly associated with accelerated FVC decline [adjusted beta of Delta FVC/year and Delta FVC %/year for asthmatics: -0.038 L (-0.054, -0.022) and -0.873% (-1.312, -0.435); adjusted beta of Delta FVC/year and Delta FVC %/year for non-asthmatics: 0.033 L (-0.042, -0.024) and -0.889% (-1.326, -0.452)]. Conclusion: Obesity is significantly associated with decreased lung function, and asthmatics had a higher risk than non-asthmatics.