title: Place of upbringing in early childhood as related to inflammatory bowel diseases in adulthood: a population-based cohort study in Northern Europe.
abstract: BACKGROUND
  The two inflammatory bowel diseases (IBD), ulcerative colitis and Crohn's disease, has increased rapidly during the twentieth century, but the aetiology is still poorly understood. Impaired immunological competence due to decreasing biodiversity and altered microbial stimulation is a suggested explanation.
  
  
  OBJECTIVE
  Place of upbringing was used as a proxy for the level and diversity of microbial stimulation to investigate the effects on the prevalence of IBD in adulthood.
  
  
  METHODS
  Respiratory Health in Northern Europe (RHINE) III is a postal follow-up questionnaire of the European Community Respiratory Health Survey (ECRHS) cohorts established in 1989-1992. The study population was 10,864 subjects born 1945-1971 in Denmark, Norway, Sweden, Iceland and Estonia, who responded to questionnaires in 2000-2002 and 2010-2012. Data were analysed in logistic and Cox regression models taking age, sex, smoking and body mass index into consideration.
  
  
  RESULTS
  Being born and raised on a livestock farm the first 5 years of life was associated with a lower risk of IBD compared to city living in logistic (OR 0.54, 95 % CI 0.31; 0.94) and Cox regression models (HR 0.55, 95 % CI 0.31; 0.98). Random-effect meta-analysis did not identify geographical difference in this association. Furthermore, there was a significant trend comparing livestock farm living, village and city living (p < 0.01). Sub-analyses showed that the protective effect was only present among subjects born after 1952 (OR 0.25, 95 % CI 0.11; 0.61).
  
  
  CONCLUSIONS
  This study suggests a protective effect from livestock farm living in early childhood on the occurrence of IBD in adulthood, however only among subjects born after 1952. We speculate that lower microbial diversity is an explanation for the findings.
authors.affiliation: Department of Public Health, Aarhus University, Bartholins Allé 2, Building 1260, 8000, Århus, Denmark, signe.timm@ph.au.dk.
authors.forename: Signe
authors.initials: S
authors.lastname: Timm
authors.forename: Cecilie
authors.initials: C
authors.lastname: Svanes
authors.forename: Christer
authors.initials: C
authors.lastname: Janson
authors.forename: Torben
authors.initials: T
authors.lastname: Sigsgaard
authors.forename: Ane
authors.initials: A
authors.lastname: Johannessen
authors.forename: Thorarinn
authors.initials: T
authors.lastname: Gislason
authors.forename: Rain
authors.initials: R
authors.lastname: Jogi
authors.forename: Ernst
authors.initials: E
authors.lastname: Omenaas
authors.forename: Bertil
authors.initials: B
authors.lastname: Forsberg
authors.forename: Kjell
authors.initials: K
authors.lastname: Torén
authors.forename: Mathias
authors.initials: M
authors.lastname: Holm
authors.forename: Lennart
authors.initials: L
authors.lastname: Bråbäck
authors.forename: Vivi
authors.initials: V
authors.lastname: Schlünssen
mesh_terms: D000328:Adult; D000368:Aged; D002675:Child, Preschool; D015331:Cohort Studies; D003093:Colitis, Ulcerative / Q000150:complications / Q000453:epidemiology*; D003424:Crohn Disease / Q000150:complications / Q000453:epidemiology*; D004781:Environmental Exposure; D005060:Europe / Q000453:epidemiology; D005260:Female; D006306:Health Surveys; D006801:Humans; D006920:Hygiene; D061148:Hygiene Hypothesis; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D016016:Proportional Hazards Models; D012111:Residence Characteristics; D012307:Risk Factors; D012424:Rural Population; D011795:Surveys and Questionnaires; D014505:Urban Population