title: Obesity is a risk factor for dyspnea but not for airflow obstruction.
abstract: BACKGROUND
  Previous research suggests that obesity is an important risk factor for asthma. However, since obesity can cause dyspnea through mechanisms other than airflow obstruction, diagnostic misclassification of asthma could partially account for this association.
  
  
  OBJECTIVE
  To determine whether there is a relationship between obesity and airflow obstruction.
  
  
  METHODS
  A total of 16 171 participants (17 years or older) from the Third National Health and Nutrition Examination Survey (NHANES III) were divided into 5 quintiles based on their body mass index (BMI) to determine the association between BMI quintile and risk of self-reported asthma, bronchodilator use, exercise performance, and airflow obstruction. Significant airflow obstruction was defined as a ratio less than 80% the predicted value of forced expiratory volume in 1 second to forced vital capacity adjusted for age, sex, and race.
  
  
  RESULTS
  The highest BMI quintile (ie, the most obese participants) had the greatest risk of self-reported asthma (odds ratio [OR], 1.50; 95% confidence interval [CI], 1.24-1.81), bronchodilator use (OR, 1.94; 95% CI, 1.38-2.72), and dyspnea with exertion (OR, 2.66; 95% CI, 2.35-3.00). Paradoxically, the highest BMI quintile had the lowest risk for significant airflow obstruction (P =.001).
  
  
  CONCLUSIONS
  This study demonstrates that while obesity is a risk factor for self-reported asthma, obese participants are at a lower risk for (objective) airflow obstruction. Many more obese than nonobese participants were using bronchodilators despite a lack of objective evidence for airflow obstruction. These data suggest that mechanisms other than airflow obstruction are responsible for dyspnea genesis in obesity and that asthma might be overdiagnosed in the obese population.
authors.affiliation: Department of Medicine, University of Alberta, Edmonton, Canada T6G 2B7. don.sin@ualberta.ca
authors.forename: Don D
authors.initials: DD
authors.lastname: Sin
authors.forename: Richard L
authors.initials: RL
authors.lastname: Jones
authors.forename: S F Paul
authors.initials: SF
authors.lastname: Man
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000402:Airway Obstruction / Q000209:etiology; D001249:Asthma / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology; D015992:Body Mass Index; D001993:Bronchodilator Agents / Q000008:administration & dosage; D004417:Dyspnea / Q000188:drug therapy / Q000209:etiology* / Q000503:physiopathology; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications* / Q000503:physiopathology; D012307:Risk Factors
chemical_list: D001993:Bronchodilator Agents