title: [The significance of conditions when growing up on the prevalence of atopy in adult Danes].
abstract: BACKGROUND
  The prevalence of atopy in adults depends on both hereditary and environmental factors. The influence of environmental factors is explained in the "hygiene hypothesis" by maturational changes in the immunological system in response to limited microbiologic challenges in early life. Several studies have indicated protective effects of varying conditions in early life, e.g., living on a farm and in particular with livestock. This study analyses this problem in a Danish population.
  
  
  METHODS
  This cross-sectional study used the European Community Respiratory Health Survey (ECRHS) protocol. A screening questionnaire concerning asthma, asthma-related symptoms and nasal allergy supplemented by questions about environmental factors was distributed to 10,000 randomly chosen individuals, 20 to 44 years of age, in five Danish counties.
  
  
  RESULTS
  The questionnaire was answered by 7,271 individuals (72.7%). The prevalence of asthma and nasal allergy in adults was independent of growing up in the city or the country, but a significant inverse association was seen when growing up in the country in proximity to livestock. This effect remained after controlling for different hereditary and environmental factors.
  
  
  CONCLUSIONS
  The results of this population-based study are consistent with the results from similar international studies. This study demonstrates that growing up in the country with contact with livestock protects against the development of asthma and nasal allergy in adults.
authors.affiliation: Vejle Sygehus, Arbejds- og Miljømedicinsk Afdeling, Odense Universitetshospital, Vejle. calyha@vs.vejleamt.dk
authors.forename: Carl Lysbeck
authors.initials: CL
authors.lastname: Hansen
authors.forename: Jesper
authors.initials: J
authors.lastname: Baelum
authors.forename: David L
authors.initials: DL
authors.lastname: Sherson
authors.forename: Lars Rauff
authors.initials: LR
authors.lastname: Skadhauge
authors.forename: Hans Christian
authors.initials: HC
authors.lastname: Siersted
authors.forename: Øyvind
authors.initials: Ø
authors.lastname: Omland
authors.forename: Torben I
authors.initials: TI
authors.lastname: Sigsgaard
mesh_terms: D000328:Adult; D000818:Animals; D000829:Animals, Domestic; D001249:Asthma / Q000209:etiology* / Q000235:genetics / Q000276:immunology; D003430:Cross-Sectional Studies; D003718:Denmark / Q000453:epidemiology; D004781:Environmental Exposure / Q000009:adverse effects; D020022:Genetic Predisposition to Disease; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000209:etiology* / Q000235:genetics / Q000276:immunology; D015995:Prevalence; D006255:Rhinitis, Allergic, Seasonal / Q000209:etiology* / Q000235:genetics / Q000276:immunology; D012307:Risk Factors; D012423:Rural Health; D011795:Surveys and Questionnaires; D014504:Urban Health