Influence of asthma and obesity on respiratory symptoms, work ability and lung function: findings from a cross-sectional Norwegian population study

BACKGROUND: Although asthma and obesity are each associated with adverse respiratory outcomes, a possible interaction between them is less studied. This study assessed the extent to which asthma and overweight/obese status were independently associated with respiratory symptoms, lung function, Work Ability Score (WAS) and sick leave; and whether there was an interaction between asthma and body mass index (BMI) ≥25 kg/m(2) regarding these outcomes. METHODS: In a cross-sectional study, 626 participants with physician-diagnosed asthma and 691 without asthma were examined. All participants completed a questionnaire and performed spirometry. The association of outcome variables with asthma and BMI category were assessed using regression models adjusted for age, sex, smoking status and education. RESULTS: Asthma was associated with reduced WAS (OR=1.9 (95% CI 1.4 to 2.5)), increased sick leave in the last 12 months (OR=1.4 (95% CI 1.1 to 1.8)) and increased symptom score (OR=7.3 (95% CI 5.5 to 9.7)). Obesity was associated with an increased symptom score (OR=1.7 (95% CI 1.2 to 2.4)). Asthma was associated with reduced prebronchodilator and postbronchodilator forced expiratory volume in 1 s (FEV(1)) (β=−6.6 (95% CI −8.2 to −5.1) and −5.2 (95% CI −6.7 to −3.4), respectively) and prebronchodilator forced vital capacity (FVC) (β=−2.3 (95% CI −3.6 to −0.96)). Obesity was associated with reduced prebronchodilator and postbronchodilator FEV(1) (β=−2.9 (95% CI −5.1 to −0.7) and −2.8 (95% CI −4.9 to −0.7), respectively) and FVC (−5.2 (95% CI −7.0 to −3.4) and −4.2 (95% CI −6.1 to −2.3), respectively). The only significant interaction was between asthma and overweight status for prebronchodilator FVC (β=−3.6 (95% CI −6.6 to −0.6)). CONCLUSIONS: Asthma and obesity had independent associations with increased symptom scores, reduced prebronchodilator and postbronchodilator FEV(1) and reduced prebronchodilator FVC. Reduced WAS and higher odds of sick leave in the last 12 months were associated with asthma, but not with increased BMI. Besides a possible association with reduced FVC, we found no interactions between asthma and increased BMI.