PURPOSE OF THE STUDY.
This cross-sectional study sought to examine the effect of childhood farm living and the degree of urbanization on the prevalence of allergic rhinitis into adulthood.
More than 30 000 questionnaires were mailed to those residents aged 16 to 75 years who lived in West Gothia, a region of Sweden.
The administered questionnaire covered topics including history of farm living for the first 5 years of life, history of physician-diagnosed obstructive respiratory disease, rhinitis, respiratory symptoms, smoking, atopic family history, and occupational and environmental exposures. The region was divided into 4 categories on the basis of population size: metropolitan areas (700 000 inhabitants), midsized towns (10 000–100 000 inhabitants), small towns (2000–10 000 inhabitants, and rural areas (<2000 inhabitants).
A total of 18 087 subjects participated in the study (62% response rate). The prevalence of allergic rhinitis was lower for those who had lived on a farm during their first 5 years of life (P < .001). This effect was seen in all age groups including 16 to 30 years (P < .001), 31 to 45 years (P = .002), 46 to 60 years (P = .001), and 61 to 75 years (P = .045). The effect was seen most strongly in the younger age group and less so for the oldest age group. The prevalence of allergic rhinitis was increased significantly in those who lived in regions with higher populations. Again, the effect was seen most strongly in the 16- to 30-year age group (P = .002). This association between farm living in the first 5 years of life and decreased allergic rhinitis continued to be significant after adjusting for confounders such as gender, family history of allergic disease, smoking, degree of urbanization, and occupational exposure.
This large-scale study found that farm living in the first 5 years of life was associated with a lower prevalence of allergic rhinitis and that this protective effect continued throughout adulthood. Increased urbanization also was associated with an increased prevalence of allergic rhinitis until 60 years of age.
Limitation of this study include self-report of allergic rhinitis and lack of a more expanded panel of questions regarding other childhood exposures. However, the results highlight the potential importance of the early childhood environment in shaping future burden of allergic disease. It has been theorized that the protective effect of farm living might be a result of exposure to endotoxin, a cell wall component of Gram-negative bacteria, which promotes nonallergic T-helper 1 responses and a shift away from T-helper 2 responses. These results show the persistence of this protective effect well into adulthood.
- Copyright © 2011 by the American Academy of Pediatrics