title: Effect of obesity on asthma phenotype is dependent upon asthma severity.
abstract: BACKGROUND
  We recently reported that obese and non-obese patients with asthma have similar airflow limitation and bronchodilator responsiveness, but obese patients have more symptoms overall. There is limited information on the effect of obesity on asthmatics of varying severity measured by objective physiological parameters. Understanding how obesity affects asthmatics of differing severity can provide insights into the pathogenesis of asthma in the obese and a rationale for the therapeutic approach to such patients.
  
  
  METHODS
  Participants with asthma from two American Lung Association--Asthma Clinical Research Center (ALA-ACRC) studies were grouped by tertiles of airflow obstruction (forced expiratory volume in one second (FEV(1)%) predicted, FEV(1)/forced vital capacity (FVC)) and methacholine reactivity (PC(20)FEV(1)). Within each tertile, we examined the independent effect of body mass index (BMI), divided into normal weight, overweight, and obese categories, on lung function, airway reactivity, and symptoms.
  
  
  RESULTS
  Overall, both FEV(1) and FVC decreased and symptoms worsened with increasing BMI; airway reactivity was unchanged. When stratified by the degree of airflow obstruction, higher BMI was not associated with greater airway reactivity to methacholine. Higher BMI was associated with more asthma symptoms only in the least obstructed FEV(1)/FVC tertile. When stratified by degree of airway reactivity, BMI was inversely associated with FVC in all PC(20)FEV(1) tertiles. BMI was directly associated with asthma symptoms only in those with the least airway reactivity.
  
  
  CONCLUSIONS
  Obesity does not influence airway reactivity in patients with asthma and it is associated with more symptoms only in those with less severe disease.
authors.affiliation: Department of Pulmonary and Critical Care Medicine, Northshore University Health System, Evanston, IL, USA.
authors.forename: Stacy
authors.initials: S
authors.lastname: Raviv
authors.forename: Anne E
authors.initials: AE
authors.lastname: Dixon
authors.forename: Ravi
authors.initials: R
authors.lastname: Kalhan
authors.forename: David
authors.initials: D
authors.lastname: Shade
authors.forename: Lewis J
authors.initials: LJ
authors.lastname: Smith
mesh_terms: D000328:Adult; D001249:Asthma / Q000150:complications / Q000503:physiopathology*; D015992:Body Mass Index; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D009765:Obesity / Q000150:complications*; D012123:Pulmonary Ventilation; D012129:Respiratory Function Tests; D014797:Vital Capacity