Farm exposure in utero may protect against asthma, hay fever and eczema

¹ Centre for Public Health Research, Research School of Public Health, Massey University, Wellington, New Zealand
² Epicentre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand
³ Research Centre for Mori Health and Development, Research School of Public Health, Massey University, Wellington, New Zealand
⁴ Malaghan Institute for Medical Research, Victoria University, Wellington, New Zealand
⁵ Dr von Hauner Children's Hospital, University of Munich, Munich, Germany

^* To whom correspondence should be addressed. E-mail: j.douwes{at}massey.ac.nz.

	Abstract

To assess which factors contribute to the lower prevalence of allergic diseases in farmers' children, and the importance of timing of exposure.

In a cross-sectional questionnaire survey we assessed asthma symptoms, hay fever and eczema as well as current, early and prenatal farm-related exposures in 1,333 farmers' children and 566 reference children aged 5–17 years.

Farmers' children had less asthma symptoms and eczema. Current and maternal exposure during pregnancy to animals and/or grain and hay reduced the risk of asthma symptoms, hay fever and eczema. The exposure-response association for maternal exposure was non-linear for most outcomes. After mutual adjustment the effects of prenatal exposure remained unchanged whereas current exposure remained protective only for asthma medication, ‘asthma ever’ and hay fever. Exposure during the first two years was not associated with symptoms after controlling for prenatal exposure. A combination of prenatal and current exposure was most strongly associated with wheeze (OR=0.48, CL=0.28–0.80), asthma medication (OR=0.50, CL=0.30–0.82), asthma ever (OR=0.50, CL=0.33–0.76), hay fever (OR=0.47, CL=0.30–0.73), and eczema (OR=0.46, CL=0.30–0.70).

Prenatal exposure may contribute to the low prevalence of asthma, hay fever and eczema in farmers' children, but continued exposure may be required to maintain optimal protection.