Early-life Farm Exposures and Adult Asthma and Atopy in the Agricultural Lung Health Study

Allergies and asthma are growing public health problems, as rates have continued to increase over the past 50 years.  In that same time period, there has been a dramatic movement of people away from farms into cities and towns.  Previous studies have suggested that these may be related and data do exist to show childhood farm animal exposures and consumption of unpasteurized milk reduces the risk of childhood asthma and allergies.  But what about early-life farm exposures and adult asthma and allergic sensitization?  In this month’s issue of JACI, House and colleagues studied more than 3000 farmers and their spouses to help answer this question (J Allergy Clin Immunol 2017; 140(1): 249-256).

Specifically, they looked at 1746 farmers and 1555 spouses from Iowa and North Carolina enrolled in the Agricultural Lung Health Study.  They used questionnaires to identify current asthma and early-life farming exposure, and then measured blood levels of allergen-specific IgE, the type of antibody that suggests allergic sensitization to a given allergen.

After analyzing all the data, they found that exposure to a farming environment when still in the womb, living on a farm when born, exposure to farm animals before the age of 6 years, and drinking raw milk were all associated with a decreased risk of allergic sensitization. Among these, the strongest association was between the mother performing farm activities while pregnant and future atopy.   There was little correlation between these factors and asthma development in adulthood.

This study builds upon previous research supporting “the hygiene hypothesis,” that is, exposures to diverse types of germs early in life promotes immune tolerance and reduces the risk of allergies throughout life.  This information can guide further research in the prevention and treatment of allergies.