Elsevier

The Lancet

Volume 358, Issue 9288, 6 October 2001, Pages 1129-1133
The Lancet

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

https://doi.org/10.1016/S0140-6736(01)06252-3Get rights and content

Summary

Background

A farming environment protects against development of asthma, hay fever, and atopic sensitisation in children. We aimed to establish whether increased exposure to microbial compounds has to occur early in life to affect maturation of the immune system and thereby reduces risk for development of allergic diseases.

Methods

We did a cross-sectional survey in rural areas of Austria, Germany, and Switzerland. 2618 (75%) of 3504 parents of 6-13-year-old children completed a standardised questionnaire on asthma, hay fever, and atopic eczema. Children from farming families, and a random sample of non-farmers' children, who gave consent for blood samples to be obtained for measurements of specific serum IgE antibodies to common allergens were invited to participate (n=901).

Findings

Exposure of children younger than 1 year, compared with those aged 1-5 years, to stables and consumption of farm milk was associated with lower frequencies of asthma (1% [3/218] vs 11% [15/138]), hay fever (3% [7] vs 13% [18]), and atopic sensitisation (12% [27] vs 29% [40]). Protection against development of asthma was independent from effect on atopic sensitisation. Continual long-term exposure to stables until age 5 years was associated with the lowest frequencies of asthma (0.8% [1/122]), hay fever (0.8% [1]), and atopic sensitisation (8.2% [10]).

Interpretation

Long-term and early-life exposure to stables and farm milk induces a strong protective effect against development of asthma, hay fever, and atopic sensitisation.

Introduction

Growing up on a farm protects against allergic sensitisation and development of childhood allergic diseases.1, 2, 3, 4, 5 Regular contact with farm animals confers an important protective effect in such an environment.2, 3 We have noted6 higher concentrations of endotoxin (lipopolysaccharide, derived from cell walls of gram-negative bacteria) in dust from kitchen floors and children's mattresses in farming families than in non-farming families. Endotoxin and other microbial compounds regulate various processes in the immune system, such as production of interleukin 12 and interferon gamma. These factors select against T-helper-2 cells and, thus, counteract allergic sensitisation.7, 8, 9, 10 The predominant type of response (T-helper-1-like or T-helper-2-like) to a specific antigen is determined at the first encounter with the antigen. In early life, the T-helper-2-polarisation of the fetal immune system is progressively replaced by T-helper-1-dominance.11, 12 Thus, microbial burden in the first years of life could be crucial for development of a non-atopic immune response. We aimed to establish whether the timing of exposure to a farming environment affects the protection such exposure confers from development of asthma, hay fever, and allergic sensitisation.

Section snippets

Participants

We did a cross-sectional survey in rural areas of Austria, Germany, and Switzerland. All these regions are fairly similar with respect to population density and farming characteristics; most farms are small and run by family members and only rarely by farm workers. 98% of these farmers own cattle, pigs, sheep, poultry, horses, or goats.2 We did fieldwork between March and July, 1999. We invited parents of 3504 children in school grades 1-6 to answer a questionnaire on respiratory and allergic

Results

Complete data were available for 812 children: 319 farmers' children with mean age 9.42 years (SD 1.63), and 493 children from non-farming families, mean age 9.49 years (1.60). 418 (51%) of all children were boys.

The odds ratios for asthma and hay fever symptoms in relation to farming status did not differ significantly between the subsample of 812 eligible children whose parents had given consent to further investigations and the total group of 2618 children whose parents had answered the

Discussion

Our results accord with findings of a lower frequency of asthma, hay fever, and atopic sensitisation in children growing up on a farm. The timing of exposure to farm characteristics in, or even before, the first year of life, and amount and duration of exposure from the first to the fifth year of life are crucial for this protective effect. An inverse relation of exposure with asthma was independent of the state of allergic sensitisation.

The mechanism by which time spent in a stable and

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