title: High altitude and chronic obstructive pulmonary disease prevalence: a casual or causal correlation?
abstract: BACKGROUND
  Studies on the relationship of chronic obstructive pulmonary disease (COPD) prevalence and altitude have reported contrasting results. The aim of this COPD case-finding study was to include a larger number of geographical sites to determine if there is an association between altitude and COPD prevalence.
  
  
  METHODS
  Individuals aged 40 or older with known COPD risk factors, whether symptomatic or not, were referred by primary-care physicians. After obtaining written informed consent, they were invited to answer a questionnaire and undergo pre- and post-bronchodilator spirometry.
  
  
  RESULTS
  Subjects were recruited in 27 Mexican cities, within an altitude range from 1 to 2,680 m above sea level. We found a weak (-0.31; P<.0001) although significant negative correlation between altitude and COPD prevalence. The COPD rate for cities located ≤1,000 m was 32.7% vs 16.4% for cities located >1,000 m (P<.0001); the rate for cities located at ≤2,000 m was 22.7% vs 15.6% for those >2,000 m; in the multiple logistic regression analysis, older age, male sex, tobacco habit, pack-years of smoking, years of exposure to biomass smoke and city altitude over sea level were significantly associated with COPD prevalence.
  
  
  CONCLUSIONS
  Our data shows a significant inverse correlation between prevalence/severity of COPD and altitude.
authors.affiliation: Facultad de Medicina, Universidad Autónoma de Baja California, Tijuana, Baja California, México. rlaniado@uabc.edu.mx
authors.forename: Rafael
authors.initials: R
authors.lastname: Laniado-Laborin
authors.forename: Adrian
authors.initials: A
authors.lastname: Rendón
authors.forename: Fernando
authors.initials: F
authors.lastname: Batiz
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Alcantar-Schramm
authors.forename: Otto
authors.initials: O
authors.lastname: Bauerle
mesh_terms: D000368:Aged; D000531:Altitude; D005260:Female; D006801:Humans; D008297:Male; D008800:Mexico; D008875:Middle Aged; D015995:Prevalence; D029424:Pulmonary Disease, Chronic Obstructive / Q000453:epidemiology* / Q000209:etiology*; D012720:Severity of Illness Index; D014504:Urban Health