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. 2015 Dec 30;13(1):93.
doi: 10.3390/ijerph13010093.

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

Signe Timm  1 , Morten Frydenberg  2 , Christer Janson  3 , Brittany Campbell  4 , Bertil Forsberg  5 , Thorarinn Gislason  6   7 , Mathias Holm  8 , Rain Jogi  9 , Ernst Omenaas  10 , Torben Sigsgaard  11 , Cecilie Svanes  12 , Vivi Schlünssen  13   14
Affiliations

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

Signe Timm et al. Int J Environ Res Public Health. .

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.

Keywords: RHINE; asthma; early life environment; farming; hygiene hypothesis; microbial exposure; urban-rural gradient.

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Figures

Figure 1
Figure 1
Cox regression subgroup analyses on asthma presented as HR adjusted for age, sex, centre, parental asthma, smoking, body silhouette at 8 years of age and parental smoking in childhood.
Figure 2
Figure 2
Cox regression analyses on asthma phenotypes presented as HR adjusted for age, sex, centre, parental asthma, smoking, body silhouette at 8 years of age and parental smoking in childhood.
Figure 3
Figure 3
Centre specific Cox regression analyses on asthma presented as HR adjusted for age, sex, centre, parental asthma, smoking, body silhouette at 8 years of age and parental smoking in childhood.
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