Pulmonary function, exhaled nitric oxide and symptoms in asthma patients with obesity: a cross-sectional study

BACKGROUND Obesity is a risk factor for the development of asthma. In patients with obesity the diagnosis of asthma is often based on symptoms, but without objective measurements. Nevertheless, obesity-associated asthma is recognized as a distinct asthma phenotype. Therefore, this study explores lung function and symptoms in asthma patients with and without obesity. METHODS The Netherlands Epidemiology of Obesity (NEO) study is a population-based cohort study with 6671 participants (aged 45-65 years) of whom 472 had asthma. Of this latter group, linear regression analysis was used to examine differences in lung function and symptoms between asthma patients with (n = 248) and without obesity (n = 224), and between asthma patients with and without increased FeNO. Analyses were adjusted for confounders. RESULTS Asthma patients with obesity had lower predicted FEV1 and FVC values than patients without obesity [adjusted mean difference (MD) -3.3% predicted, 95% CI -6.5, -0.2; adjusted MD -5.0% predicted, 95% CI -7.8, -2.1]. The prevalence of symptoms was higher in patients with obesity. Asthma patients with obesity and with increased FeNO had lower FEV1 and FEV1/FVC values compared with those with low FeNO (adjusted MD -6.9% predicted, 95% CI -11.7, -2.0; -2.4%, 95% CI -4.6, -0.2). CONCLUSION Asthma patients with obesity had lower FEV1 and FVC values than patients without obesity. This suggests that patients with obesity have restrictive lung function changes, rather than obstructive changes. Asthma patients with obesity and increased FeNO showed more obstructive changes. FeNO might help to identify patients with eosinophilic inflammation-driven asthma, whereas patients with low FeNO might have an obesity-associated asthma phenotype in which symptoms are partly caused by the obesity.