title: Effect of obesity on airway inflammation: a cross-sectional analysis of body mass index and sputum cell counts.
abstract: BACKGROUND
  Several observational studies have demonstrated an association between obesity and asthma. Studies evaluating exhaled nitric oxide levels and obesity have revealed that a higher body mass index (BMI) is associated with elevated exhaled nitric oxide levels. Airway inflammation using sputum cell counts has not been assessed in obese patients with airway diseases.
  
  
  OBJECTIVE
  The primary aim of this study was to determine whether obesity (based on BMI) is associated with eosinophilic or neutrophilic bronchitis.
  
  
  METHODS
  The results from a database of induced sputum cell counts were compared with BMI and analysed using correlation statistics, regression and parametric and non-parametric analysis.
  
  
  RESULTS
  Seven-hundred and twenty-seven adult participants with an equal number of sputum samples were included in the analysis. BMI varied from 14.5 to 55 kg/m(2). Sputum total cell count (mean+/-SD: 12.9 x 10(6) cell/g+/-21.5), eosinophil percent (median; min to max: 0.3%; 0-89.0), and neutrophil percent (mean+/-SD: 63.5+/-26.6%) were within normal limits. Participants with asthma had a higher percentage of sputum eosinophils than those without asthma (P=0.01). However, there was no difference in the total or differential cell counts among the obese and non-obese participants, when the data were analysed according to BMI category, gender, dose of inhaled corticosteroid, and presence or absence of asthma.
  
  
  CONCLUSIONS
  In this large sample of adult asthmatic and non-asthmatic participants, there was no association between BMI and airway inflammation measured by sputum cell counts. Other mechanisms to explain the relationship between obesity and asthma will need to be explored if this association is to be better understood.
authors.affiliation: Department of Medicine, Firestone Institute for Respiratory Health, St. Joseph's Healthcare, McMaster University, Hamilton, ON, Canada.
authors.forename: D C
authors.initials: DC
authors.lastname: Todd
authors.forename: S
authors.initials: S
authors.lastname: Armstrong
authors.forename: L
authors.initials: L
authors.lastname: D'Silva
authors.forename: C J
authors.initials: CJ
authors.lastname: Allen
authors.forename: F E
authors.initials: FE
authors.lastname: Hargreave
authors.forename: K
authors.initials: K
authors.lastname: Parameswaran
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001249:Asthma / Q000097:blood / Q000209:etiology* / Q000503:physiopathology; D015992:Body Mass Index; D001991:Bronchitis / Q000097:blood / Q000209:etiology* / Q000503:physiopathology; D003430:Cross-Sectional Studies; D019992:Databases as Topic; D004804:Eosinophils; D005260:Female; D006801:Humans; D007958:Leukocyte Count; D008297:Male; D008875:Middle Aged; D009504:Neutrophils; D009765:Obesity / Q000097:blood / Q000150:complications* / Q000503:physiopathology; D012189:Retrospective Studies; D013147:Spirometry; D013183:Sputum / Q000166:cytology*