title: The Urban-Rural Gradient In Asthma: A Population-Based Study in Northern Europe.
abstract: The early life environment appears to have a persistent impact on asthma risk. We hypothesize that environmental factors related to rural life mediate lower asthma prevalence in rural populations, and aimed to investigate an urban-rural gradient, assessed by place of upbringing, for asthma. The population-based Respiratory Health In Northern Europe (RHINE) study includes subjects from Denmark, Norway, Sweden, Iceland and Estonia born 1945-1973. The present analysis encompasses questionnaire data on 11,123 RHINE subjects. Six categories of place of upbringing were defined: farm with livestock, farm without livestock, village in rural area, small town, city suburb and inner city. The association of place of upbringing with asthma onset was analysed with Cox regression adjusted for relevant confounders. Subjects growing up on livestock farms had less asthma (8%) than subjects growing up in inner cities (11%) (hazard ratio 0.72 95% CI 0.57-0.91), and a significant urban-rural gradient was observed across six urbanisation levels (p = 0.02). An urban-rural gradient was only evident among women, smokers and for late-onset asthma. Analyses on wheeze and place of upbringing revealed similar results. In conclusion, this study suggests a protective effect of livestock farm upbringing on asthma development and an urban-rural gradient in a Northern European population.
authors.affiliation: Department of Public Health, Danish Ramazzini Centre, Aarhus University, DK-8000 Aarhus C, Denmark. signe.timm@ph.au.dk.
authors.forename: Signe
authors.initials: S
authors.lastname: Timm
authors.affiliation: Department of Public Health, Danish Ramazzini Centre, Aarhus University, DK-8000 Aarhus C, Denmark. morten@ph.au.dk.
authors.forename: Morten
authors.initials: M
authors.lastname: Frydenberg
authors.affiliation: Department of Medical Sciences: Respiratory, Allergy and Sleep Research, Uppsala University, 751 05 Uppsala, Sweden. christer.janson@medsci.uu.se.
authors.forename: Christer
authors.initials: C
authors.lastname: Janson
authors.affiliation: Allergy and Lung Health Unit, Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Victoria 3010, Australia. brittany.campbell@unimelb.edu.au.
authors.forename: Brittany
authors.initials: B
authors.lastname: Campbell
authors.affiliation: Division of Occupational and Environmental Medicine, Department of Public Health and Clinical Medicine, Umeå University, 901 87 Umeå, Sweden. bertil.forsberg@envmed.umu.se.
authors.forename: Bertil
authors.initials: B
authors.lastname: Forsberg
authors.affiliation: Department of Respiratory Medicine and Sleep, Landspitali University Hospital, Reykjavik IS-108, Iceland. thorarig@landspitali.is.|Faculty of Medicine, University of Iceland, Reykjavik IS-101, Iceland. thorarig@landspitali.is.
authors.forename: Thorarinn
authors.initials: T
authors.lastname: Gislason
authors.affiliation: Department of Occupational and Environmental Medicine, Sahlgrenska University Hospital, Gothenburg 405 30, Sweden. mathias.holm@amm.gu.se.
authors.forename: Mathias
authors.initials: M
authors.lastname: Holm
authors.affiliation: Lung Clinic, Tartu University Hospital, Tartu 50406, Estonia. Rain.Jogi@kliinikum.ee.
authors.forename: Rain
authors.initials: R
authors.lastname: Jogi
authors.affiliation: Institute of Clinical Science, University of Bergen, 5020 Bergen, Norway. ernst.omenaas@helse-bergen.no.
authors.forename: Ernst
authors.initials: E
authors.lastname: Omenaas
authors.affiliation: Department of Public Health, Danish Ramazzini Centre, Aarhus University, DK-8000 Aarhus C, Denmark. ts@ph.au.dk.
authors.forename: Torben
authors.initials: T
authors.lastname: Sigsgaard
authors.affiliation: Institute of Clinical Science, University of Bergen, 5020 Bergen, Norway. cecilie.svanes@helse-bergen.no.
authors.forename: Cecilie
authors.initials: C
authors.lastname: Svanes
authors.affiliation: Department of Public Health, Danish Ramazzini Centre, Aarhus University, DK-8000 Aarhus C, Denmark. vs@ph.au.dk.|National Research Center for Working Environment, Copenhagen DK-2100, Denmark. vs@ph.au.dk.
authors.forename: Vivi
authors.initials: V
authors.lastname: Schlünssen
mesh_terms: D000328:Adult; D001249:Asthma / Q000453:epidemiology* / Q000209:etiology; D003430:Cross-Sectional Studies; D005060:Europe / Q000453:epidemiology; D005260:Female; D006306:Health Surveys; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D016016:Proportional Hazards Models; D065840:Protective Factors; D012111:Residence Characteristics; D012307:Risk Factors; D012423:Rural Health / Q000706:statistics & numerical data*; D011795:Surveys and Questionnaires; D014504:Urban Health / Q000706:statistics & numerical data*
keywords: RHINE; asthma; early life environment; farming; hygiene hypothesis; microbial exposure; urban-rural gradient