title: Low prevalence of atopy in young Danish farmers and farming students born and raised on a farm.
abstract: BACKGROUND
  Recent studies have shown that in several countries atopic sensitization to common allergens (common atopy) and atopic symptoms are markedly less prevalent in children living on a farm, compared with non-farm children living in the same rural areas. Living conditions on farms may, however, vary largely between different countries. It is also not yet known whether the "protective" effect of a farm environment can also be found in adults.
  
  
  METHODS
  Common atopy and respiratory health were assessed by skin prick tests (SPT), questionnaire and measurement of bronchial hyper-responsiveness (BHR) in the Sund Stald (SUS) study, a cohort study on respiratory health in Danish farming students and conscripts from the same rural areas as controls. Results of SPT were confirmed by IgE serology in all SPT+ subjects and a subset of SPT- subjects. Prevalences of common atopy, respiratory symptoms and bronchial hyper- responsiveness were compared for farmers and controls, and for those who had or had not lived on a farm in early childhood.
  
  
  RESULTS
  In multiple logistic regression analyses adjusting for ever smoking and a familial history of allergy, both being a farmer (ORs 0.62-0.75) and having had a farm childhood (ORs 0.55-0.75) appeared to contribute independently to a lower risk of sensitization to common allergens as assessed by SPT and IgE serology. A farm childhood was also inversely associated with high total IgE (OR 0.68), presence of respiratory symptoms (ORs 0.69-0.79) and BHR (OR 0.61) in these analyses. Direction and strength of the association between being a farmer and respiratory symptoms or BHR varied widely (ORs 0.69-1.28).
  
  
  CONCLUSIONS
  The "anti-atopy" protective effect of a farm childhood could be confirmed in Danish farming students: prevalences of positive SPT, specific and total IgE, allergic symptoms and BHR were lower in those being born or raised on a farm. Past exposure to the farm environment in early childhood may therefore also contribute to a lower risk of atopic sensitization and disease at a later age.
authors.affiliation: Institute for Risk Assessment Sciences (IRAS), Utrecht University, Utrecht, The Netherlands.
authors.forename: L
authors.initials: L
authors.lastname: Portengen
authors.forename: T
authors.initials: T
authors.lastname: Sigsgaard
authors.forename: Ø
authors.initials: Ø
authors.lastname: Omland
authors.forename: C
authors.initials: C
authors.lastname: Hjort
authors.forename: D
authors.initials: D
authors.lastname: Heederik
authors.forename: G
authors.initials: G
authors.lastname: Doekes
mesh_terms: D000328:Adult; D000383:Agriculture / Q000193:education; D000485:Allergens / Q000276:immunology; D016535:Bronchial Hyperreactivity / Q000453:epidemiology; D003718:Denmark; D004777:Environment; D006801:Humans; D006967:Hypersensitivity / Q000453:epidemiology*; D007114:Immunization; D007073:Immunoglobulin E / Q000032:analysis; D015995:Prevalence; D012120:Respiration Disorders / Q000453:epidemiology; D012882:Skin Tests; D013334:Students
chemical_list: D000485:Allergens; D007073:Immunoglobulin E