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

Abstract Background Previous studies, mostly from Europe, suggest that early-life farming exposures protect against childhood asthma and allergy; few data exist on asthma and allergy in adults. Objective To examine associations between early-life farming exposures and current asthma and atopy in an older adult US farming population. Methods We analyzed data from 1,746 farmers and 1,555 spouses (mean age=63) from a case-control study nested within the Agricultural Health Study. Current asthma and early-life farming exposures were assessed via questionnaires. We defined atopy based on specific IgE>0.70 IU/ml to at least one of ten allergens measured in blood. We used logistic regression, adjusted for age, sex, race, state (Iowa or North Carolina), and smoking (pack-years), to estimate associations between early-life exposures and asthma (1,198 cases and 2,031 non-cases) or atopy (578 cases and 2,526 non-cases). Results Exposure to the farming environment in utero and in early childhood had little or no association with asthma but was associated with reduced odds of atopy. The strongest association was seen for having a mother who performed farm activities while pregnant (Odds Ratio=0.60, 95% Confidence Interval=0.48-0.74) and remained significant in models with correlated early-life exposures including early childhood farm animal contact and raw milk consumption. Conclusions In a large US farming population, early-life farm exposures, particularly maternal farming activities while pregnant, were strongly associated with reduced risk of atopy in adults. These results extend previous work done primarily on childhood outcomes and suggest that protective associations of early-life farming exposures on atopy endure across the life-course.