Background: Several studies have suggested a relationship between asthma and obesity; however, this relationship is unclear when obesity is compared with bronchial hyperresponsiveness to methacholine.

Aim: To determine whether obesity is associated with a diagnosis of asthma.

Methods: We conducted a cross-sectional study in a population of Spanish adults in the north of Madrid, Spain between 2003 and 2007. The patients included had experienced asthma symptoms during the previous year, but had a ratio of forced expiratory volume in
the first second of expiration (FEV1) to forced vital capacity (FVC) of >70%. Diagnosis was confirmed by the presence of symptoms and demonstration of bronchial hyperresponsiveness to methacholine. Obesity was measured by body mass index (BMI Adjusted odd ratios (OR) were obtained by logistic regression.

Results: Of a total of 1424 patients included, 251 (17.6%) were diagnosed with asthma. These patients were younger (P<.001) and had lower BMI (P<.001) and lung function parameters (FEV1 and FEV1/FVC ratio) than individuals without asthma (P<.001). After adjusting the model for age, gender, baseline FEV1, and FEV1/FVC ratio, patients with overweight or obesity were not more frequently diagnosed with asthma than those with normal weight (OR, 0.848 [95% confidence interval (CI), 0.59-1.20]; and OR, 0.616 [95% CI, 0.38-0.99], respectively). In addition, obese males were more frequently diagnosed with asthma than obese females (P<.041).

Conclusions: In this study, obesity and overweight were not associated with a diagnosis of asthma based on the presence of consistent symptoms and demonstration of airway responsiveness to methacholine.

Key words: Asthma. Obesity. Body mass index. Airway hyperresponsiveness.