The Urban-Rural Gradient In Asthma: A Population-Based Study in Northern Europe.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked Files. This article is open access.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.Faculty of Health, Aarhus University, Denmark 240008 Wood Dust Foundation 444508795 Danish Lung Association Swedish Heart and Lung Foundation Swedish Association Against Asthma and Allergy Swedish Association against Heart and Lung Disease Swedish Council for Working Life and Social Research Bror Hjerpstedt Foundation Vardal Foundation for Health Care and Allergic Researce Norwegian Research Council 135773/330 Norwegian Asthma and Allergy Association Icelandic Research Council Estonian Science Foundation 435