Environmental and occupational respiratory disorders
Which aspects of the farming lifestyle explain the inverse association with childhood allergy?

https://doi.org/10.1016/j.jaci.2006.03.008Get rights and content

Background

Farmers' children have a reduced prevalence of allergic disorders. The specific protective environmental factors responsible are not yet identified.

Objective

We sought to determine whether farmers' children in the rural county of Shropshire, England, have a reduced risk of atopy and, if so, to identify the factors responsible.

Methods

The Study of Asthma and Allergy in Shropshire was a 2-stage cross-sectional study. In stage 1 a questionnaire to elicit allergic status, diet, and farming exposure was completed by the parents of 4767 children. In stage 2 a stratified subsample of 879 children underwent skin prick testing and measurement of domestic endotoxin.

Results

Compared with rural nonfarming children, farmers' children had significantly less current asthma symptoms (adjusted odds ratio (OR), 0.67; 95% CI, 0.49-0.91; P = .01) and current seasonal allergic rhinitis (adjusted OR, 0.50; 95% CI, 0.33-0.77; P = .002) but not current eczema symptoms (adjusted OR, 0.91; 95% CI, 0.68-1.21; P = .53) or atopy (adjusted OR, 0.68; 95% CI, 0.40-1.16; P = .15). In contrast, current unpasteurized milk consumption was associated with significantly less current eczema symptoms (adjusted OR, 0.59; 95% CI, 0.40-0.87; P = .008) and a greater reduction in atopy (adjusted OR, 0.24; 95% CI, 0.10-0.53; P = .001). The effect was seen in all children, independent of farming status. Unpasteurized milk consumption was associated with a 59% reduction in total IgE levels (P < .001) and higher production of whole blood stimulated IFN-γ (P = .02).

Conclusion

Unpasteurized milk consumption was the exposure mediating the protective effect on skin prick test positivity. The effect was independent of farming status and present with consumption of infrequent amounts of unpasteurized milk.

Clinical implications

Unpasteurized milk might be a modifiable influence on allergic sensitization in children.

Section snippets

Study participants

The Study of Asthma and Allergy in Shropshire took place in 2 stages. Shropshire was chosen because it was believed to have a mix of farming types. An initial questionnaire was sent to all the children in rural primary schools with significant numbers of farming children attending. The aim was to identify parent-reported symptoms of asthma, eczema, and allergic rhinitis by using questions from the International Study of Asthma and Allergy in Childhood.14 A food-frequency questionnaire that

Results

A response rate of 66.0% (4767/7226) was achieved from the primary survey. This was less than had been anticipated; however, distribution of the questionnaires coincided with the worst flooding in Shropshire since 1947. Invitations to participate in the second stage of the study were sent to 1458 children, of whom 1073 (73.6%) replied and 944 (64.7%) consented to participate in one or more parts of the second stage. The actual number participating in the allergy tests was 879 (60.3%), with the

Discussion

Our study found a significantly lower prevalence among farmers' children of current asthma and seasonal allergic rhinitis symptoms but not current eczema symptoms. A nonsignificant reduced rate of atopy among farming children was also observed. However, the effect estimate for atopy was consistent with a meta-analysis of the published farming studies to date (our effect, 0.68; fixed effects pooled estimate, 0.59; 95% CI, 0.52-0.68; P < .001).2, 4, 5, 7, 10, 11, 12, 13 Similar consistency was

References (24)

  • J. Riedler et al.

    Exposure to farming in early life and development of asthma and allergy: a cross-sectional survey

    Lancet

    (2001)
  • E. Chrischilles et al.

    Asthma prevalence and morbidity among rural Iowa schoolchildren

    J Allergy Clin Immunol

    (2004)
  • Ch Braun-Fahrländer et al.

    Lower risk of allergic sensitization and hay fever in farmers' children in Switzerland

    Epidemiology

    (1996)
  • C.h. Braun-Fahrländer et al.

    Prevalence of hay fever and allergic sensitization in farmer's children and their peers living in the same rural community

    Clin Exp Allergy

    (1999)
  • O.S. von Ehrenstein et al.

    Reduced risk of hay fever and asthma among children of farmers

    Clin Exp Allergy

    (2000)
  • J. Riedler et al.

    Austrian children living on a farm have less hay fever, asthma and allergic sensitization

    Clin Exp Allergy

    (2000)
  • C. Braun-Fahrländer et al.

    Environmental exposure to endotoxin and its relation to asthma in school-age children

    N Engl J Med

    (2002)
  • S.H. Downs et al.

    Having lived on a farm and protection against allergic diseases in Australia

    Clin Exp Allergy

    (2001)
  • M. Kilpeläinen et al.

    Farm environment in childhood prevents the development of allergies

    Clin Exp Allergy

    (2000)
  • S.T. Remes et al.

    Does heredity modify the association between farming and allergy in children?

    Acta Paediatr

    (2002)
  • S.T. Remes et al.

    Which factors explain the lower prevalence of atopy amongst farmers' children?

    Clin Exp Allergy

    (2003)
  • P. Ernst et al.

    Relative scarcity of asthma and atopy among rural adolescents raised on a farm

    Am J Respir Crit Care Med

    (2000)
  • Cited by (0)

    Supported through a Wellcome Research Training Fellowship in Clinical Epidemiology (grant no. 056906/Z/99/Z) held by Dr Perkin.

    Disclosure of potential conflict of interest: The authors have declared that they have no conflict of interest.

    View full text