Early Exposure to Farm Allergens Improves Adult Lung Function, Reduces Rates of Allergies

• Study found beneficial effects of early farm life on sensitization, asthma, rhinitis, and bronchial hyper-responsiveness.
• Researchers examined adults more than 10,000 adults from 14 countries.
• Children raised on farms were 54% less likely to develop asthma or hay fever and 57 percent less likely to have nasal allergies than children raised in cities.
• Children raised on farms were also 50% less likely to develop asthma than children raised in cities.
• Female children raised on farms in all of the 14 countries studied had superior lung function as adults than did women who grew up in cities.

Additional Support for the Hygiene Hypothesis

Children raised on farms (Figure 1) and exposed early in life to farm allergens from pets and plants had superior lung function and lower rates of allergies as adults compared to children who lived in cities. A study published recently in Thorax offered these and other results based on examination of >10,000 adults in 14 countries.

Specifically, the study found that early-life exposure to allergens typically found on farms in 14 countries, as well as other biodiversity proxies, was associated with improved adult forced expiratory volume in 1 second (FEV₁; Figure 2). Similarly, the report suggested beneficial effects of early farm life on sensitization, asthma, rhinitis bronchial hyper-responsiveness (BHR).

“This is the first study to report beneficial effects of growing up on a farm on adult FEV1. Our study confirmed the beneficial effects of early farm life on sensitization, asthma and rhinitis, and found a similar association for BHR. In persons with an urban upbringing, a higher biodiversity score predicted less allergic sensitization, but to a lesser magnitude than a childhood farm environment,” the authors concluded.

The Analysis

The European Community Respiratory Health Survey II examined 10,201 participants aged 26–54 years from 14 countries in Europe, Scandinavia and Australia. The survey including participants' place of upbringing (farm, rural environment or inner city) before age 5 years. The researchers composed a biodiversity score based on childhood exposure to cats, dogs, day care, bedroom sharing, and older siblings. The researchers then examined associations of the biodiversity score with lung function, BHR, allergic sensitization (Figure 3), asthma (Figure 4), and rhinitis.

Compared with children raised in an urban or suburban setting, those with early-life exposure to allergens commonly present on farms in 14 countries had less:

• Atopic sensitization (adjusted OR 0.46, 95% CI 0.37 to 0.58)
• Atopic BHR (0.54 (0.35 to 0.83))
• Atopic asthma (0.47 (0.28 to 0.81))
• Atopic rhinitis (0.43 (0.32 to 0.57))

They did not, however, have fewer non-atopic outcomes. Less pronounced protective effects were observed for rural environment exposures. Women with a farm upbringing had higher FEV₁ (adjusted difference 110 mL (64 to 157)), independent of sensitization and asthma. In an inner-city environment, a higher biodiversity score was related to less allergic sensitization.

Conclusions

Nearly 64% of participants said they spent the first 5 years of life in a rural village, small town, or city suburb. About 27% lived in a city and about 9% grew up on a farm.

Children who spent the early years of their lives on a farm were more likely to have had pets and older brothers or sisters. These children were also more likely to have shared a bedroom with a sibling. They were less likely to have had a close family member with allergies.

Children raised on farms were 54% less likely to develop asthma or hay fever and 57% less likely to have developed allergic rhinitis as adults than were children raised in cities. Children raised on farms were 50% less likely to develop asthma as adolescents or adults than were children raised in any other setting.

Women who were raised on farms had higher FEV₁ (adjusted difference 110 mL (64 to 157)) than those raised in any other setting, independent of sensitization and asthma.