title: The Danish urban-rural gradient of allergic sensitization and disease in adults.
abstract: BACKGROUND
  The reported prevalence of allergic sensitization among children is lower in rural areas than in urban areas of the world. The aim was to investigate the urban-rural differences of allergic sensitization to inhalant allergens in adults depending on childhood exposure living in an industrialized country as Denmark.
  
  
  METHODS
  A total of 1236 male participants of 30-40 years of age recruited from two epidemiological studies were divided into four groups with regard to place of upbringing; city, town, rural area and farm. Allergic sensitization was assessed by skin prick tests (SPTs) to 10 inhalant allergens and measurements of serum specific IgE (sIgE) to four inhalant allergens (grass, birch, cat and house dust mite).
  
  
  RESULTS
  The prevalence of allergic sensitization to inhalant allergens decreased with decreasing degree of urbanized childhood. The risk of being sensitized to one or more allergens also decreased with decreasing degree of urbanized upbringing measured by sIgE to 4 common allergens as odds ratio with 95% confidence intervals with city as reference; town 0.60 (0.39-0.92), rural area 0.34 (0.22-0.52) and farm 0.31 (0.21-0.46). Furthermore, it was measured by SPT to 10 common allergens; town 0.52 (0.33-0.84), rural area 0.34 (0.21-0.53) and farm 0.29 (0.19-0.45). This urban-rural association was also seen for the risk of sensitization to specific allergens, rhinitis and allergic asthma.
  
  
  CONCLUSIONS
  This is the first study to show an urban-rural gradient of overall allergic sensitization and specific allergen sensitization in adults depending on their childhood exposure. In this highly homogenous western population, exposure to a less urbanized childhood was associated with lower risk of allergic sensitization and disease as an adult.
authors.affiliation: Section for Environment Occupation and Health, Department of Public Health, Aarhus University, Aarhus, Denmark.
authors.forename: G
authors.initials: G
authors.lastname: Elholm
authors.affiliation: Research Centre for Prevention and Health, The Capital Region of Denmark, Copenhagen, Denmark.|Department of Clinical Experimental Research, Glostrup University Hospital, Glostrup, Denmark.|Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Linneberg
authors.affiliation: Research Centre for Prevention and Health, The Capital Region of Denmark, Copenhagen, Denmark.
authors.forename: L L N
authors.initials: LL
authors.lastname: Husemoen
authors.affiliation: Clinic of Occupational Medicine, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: Ø
authors.initials: Ø
authors.lastname: Omland
authors.affiliation: Research ALK Abelló, ALK Abelló, Hørsholm, Denmark.
authors.forename: P M
authors.initials: PM
authors.lastname: Grønager
authors.affiliation: Section for Environment Occupation and Health, Department of Public Health, Aarhus University, Aarhus, Denmark.
authors.forename: T
authors.initials: T
authors.lastname: Sigsgaard
authors.affiliation: Section for Environment Occupation and Health, Department of Public Health, Aarhus University, Aarhus, Denmark.
authors.forename: V
authors.initials: V
authors.lastname: Schlünssen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000485:Allergens / Q000276:immunology; D000818:Animals; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D006967:Hypersensitivity / Q000175:diagnosis / Q000453:epidemiology* / Q000276:immunology; D007114:Immunization; D007073:Immunoglobulin E / Q000097:blood / Q000276:immunology; D008297:Male; D008875:Middle Aged; D018570:Risk Assessment; D012307:Risk Factors; D012424:Rural Population; D012882:Skin Tests; D011795:Surveys and Questionnaires; D014505:Urban Population; D055815:Young Adult
chemical_list: D000485:Allergens; D007073:Immunoglobulin E
keywords: adults; allergy; environmental exposure; homogenous population; industrialized country; urbanization