BACKGROUND Obesity is a risk factor for asthma in the general population, but the effect of obesity on airway hyperresponsiveness (AFHR) or airway inflammation in asthma is not clear. This study evaluated the relationship between obesity and asthma, assessing aspects of symptoms, AHR, and severity.

METHODS In total, 852 patients with asthma diagnosed by asthma specialists based on AHR as confirmed by a methacholine bronchial provocation test, were enrolled from the Cohort for Reality and Evolution of Adult Asthma in Korea (COREA) adult asthma cohort. The intensity of AHR was assessed by the concentration of methacholine needed to cause a 20% decrease in FEV(1) (PC(20)). Patients were classified into four categories based on body mass index (BMI): underweight (<18.5), normal weight (18.5-24.9), overweight (25.0-29.9), and obese (≥30).

RESULTS BMI was negatively correlated with FEV(1) (l), FVC (l), and FEV(1)/FVC (%) in lung function tests. The prevalence of wheezing increased with higher BMI after adjustment for age, sex, smoking, medication history, and PC(20) (p < 0.0001). logPC(20) was lower in the normal weight group compared with the overweight group (p = 0.003). The risk of moderate or severe AHR (PC(20) ≤ 4 mg/ml) decreased with increased BMI after adjustment for age, sex, smoking, and medication history (p = 0.035).

CONCLUSIONS Obesity is a risk factor for asthma in the general population, but obesity in asthmatic patients is negatively correlated with the intensity of AHR and is not related to asthma severity. Obesity is positively related with the prevalence of wheezing but negatively related to AHR in asthmatic patients.