title: The interplay between the effects of lifetime asthma, smoking, and atopy on fixed airflow obstruction in middle age.
abstract: BACKGROUND
  The contribution by asthma to the development of fixed airflow obstruction (AO) and the nature of its effect combined with active smoking and atopy remain unclear.
  
  
  OBJECTIVE
  To investigate the prevalence and relative influence of lifetime asthma, active smoking, and atopy on fixed AO in middle age.
  
  
  METHODS
  The population-based Tasmanian Longitudinal Health Study cohort born in 1961 (n = 8,583) and studied with prebronchodilator spirometry in 1968 was retraced (n = 7,312) and resurveyed (n = 5,729 responses) from 2002 to 2005. A sample enriched for asthma and chronic bronchitis underwent a further questionnaire, pre- and post-bronchodilator spirometry (n = 1,389), skin prick testing, lung volumes, and diffusing capacity measurements. Prevalence estimates were reweighted for sampling fractions. Multiple linear and logistic regression were used to assess the relevant associations.
  
  
  RESULTS
  Main effects and interactions between lifetime asthma, active smoking, and atopy as they relate to fixed AO were measured. The prevalence of fixed AO was 6.0% (95% confidence interval [CI], 4.5-7.5%). Its association with early-onset current clinical asthma was equivalent to a 33 pack-year history of smoking (odds ratio, 3.7; 95% CI, 1.5-9.3; P = 0.005), compared with a 24 pack-year history for late-onset current clinical asthma (odds ratio, 2.6; 95% CI, 1.03-6.5; P = 0.042). An interaction (multiplicative effect) was present between asthma and active smoking as it relates to the ratio of post-bronchodilator FEV(1)/FVC, but only among those with atopic sensitization.
  
  
  CONCLUSIONS
  Active smoking and current clinical asthma both contribute substantially to fixed AO in middle age, especially among those with atopy. The interaction between these factors provides another compelling reason for atopic individuals with current asthma who smoke to quit.
authors.affiliation: Centre for Molecular, Environmental, Genetic, and Analytical Epidemiology, University of Melbourne, Victoria, Australia. j.perret@student.unimelb.edu.au
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Perret
authors.forename: Shyamali C
authors.initials: SC
authors.lastname: Dharmage
authors.forename: Melanie C
authors.initials: MC
authors.lastname: Matheson
authors.forename: David P
authors.initials: DP
authors.lastname: Johns
authors.forename: Lyle C
authors.initials: LC
authors.lastname: Gurrin
authors.forename: John A
authors.initials: JA
authors.lastname: Burgess
authors.forename: John
authors.initials: J
authors.lastname: Marrone
authors.forename: James
authors.initials: J
authors.lastname: Markos
authors.forename: Stephen
authors.initials: S
authors.lastname: Morrison
authors.forename: Iain
authors.initials: I
authors.lastname: Feather
authors.forename: Paul S
authors.initials: PS
authors.lastname: Thomas
authors.forename: Christine F
authors.initials: CF
authors.lastname: McDonald
authors.forename: Graham G
authors.initials: GG
authors.lastname: Giles
authors.forename: John L
authors.initials: JL
authors.lastname: Hopper
authors.forename: Richard
authors.initials: R
authors.lastname: Wood-Baker
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Abramson
authors.forename: Eugene H
authors.initials: EH
authors.lastname: Walters
mesh_terms: D000328:Adult; D017668:Age of Onset; D000402:Airway Obstruction / Q000150:complications / Q000503:physiopathology*; D001249:Asthma / Q000150:complications / Q000453:epidemiology / Q000503:physiopathology*; D005260:Female; D006304:Health Status; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011653:Pulmonary Diffusing Capacity; D012907:Smoking / Q000009:adverse effects / Q000503:physiopathology*; D013147:Spirometry; D013997:Time Factors