Early-life exposure to farm environments is protective against subsequent adult allergic diseases including asthma, concludes a study spanning 14 countries including Australia.
According to the research team, led by Professor Shyamali Dharmage from the Allergy and Lung Health Unit at the University of Melbourne, the consistency of their findings suggest that common biological factors, rather than social or cultural ones, may have a role to play.
The observational European Community Respiratory Health Survey II included more than 10,000 adults from 14 countries in Europe, Scandinavia, and Australia.
A ‘biodiversity score’ from 0-5 was calculated for each participant based on their reported exposure to pet cats and dogs; older siblings; and other children.
Lung function (assessed by measuring FEv1) and antibody (IgE) levels were tested and participants also completed a questionnaire on allergic symptoms, including nasal symptoms, asthma, hay fever, wheeze, and bronchial hyper-responsiveness.
Results showed that children who grew up on a farm were more likely to have had pets, older siblings, and to have shared a bedroom in their early childhood.
As adults this group were less likely to be sensitised to allergens, have nasal symptoms, or to have over reactive airways compared to the adults who spent the early years of their life in other environments.
They were also 54% less likely to have asthma, or hay fever and 57% less likely to have allergic nasal symptoms than those living in an inner city.
Pooled analysis of the data showed that adults who had lived on farms as a child were 53% less likely to be sensitised to allergens than those living in urban areas, while children who grew up in a village were 26% less likely to be sensitised.
The researchers said a novel finding from the study was that women who grew up on a farm had higher lung function (FEV1 (adjusted difference 110 mL (64 to 157)), independent of sensitisation and asthma. However they conceded that more work was needed to confirm these gender differences.
“The overall findings from our analysis indicate that the diversity of early-life microbial exposures impacts disease outcomes later in adult life,” they concluded in the paper published in Thorax.