Farm life safeguards children against allergic rhinitis
Growing up on a farm appears to confer a reduced risk of developing allergic rhinitis in children, with the protective effect of farm living being set until school age and sustained through early adulthood.
In the Genetic and Environmental Causes of Asthma in the European Community (GABRIEL) study, the prevalence of allergic rhinitis symptoms among children aged 6–11 years (baseline) was lower for those who did vs did not live on a farm (4 percent vs 10 percent). At follow-up, when the participants were aged 20–25 years, the prevalence increased in both groups but remained significantly decreased among those who had lived on a farm during childhood (10 percent vs 24 percent; p<0.001). [J Allerg Clin Immunol 2022;150:1209-1215.E2]
Multivariable analysis confirmed that the odds of experiencing symptoms of allergic rhinitis at follow-up were lower among participants who had always lived on a farm (odds ratio [OR], 0.35, 95 percent confidence interval [CI], 0.20–0.62) and among those who gave up farm living (OR, 0.36, 95 percent CI, 0.17–0.77) as opposed to those who had never lived on a farm.
“By following our cohort from childhood to adulthood, we were able to provide evidence that the protective effect of growing up on a farm on development of allergic rhinitis persists into young adulthood, even if the study participants had moved away from the farm after the age of 6–12 years,” according to the investigators.
“Likewise, we did not see an additional benefit of continued farm exposure from adolescence to young adulthood. The prevalence of allergic rhinitis symptoms more than doubled from childhood to adulthood irrespective of farm contact, although participants who had lived on a farm started from a lower prevalence level,” they added.
For symptoms of wheeze, the investigators found no statistically significant association with farm living. They attributed this null association to the low prevalence of wheeze combined with the diverse phenotypes of asthma, given that microbial exposures in the farm environment are thought to mainly protect against atopic asthma. [BMJ Open 2019;9e027808]
GABRIEL involved 2,276 participants, among whom 1,501 (66 percent) completed the follow-up questionnaire and 1,333 were included in the analyses. About half of the population was female, and those who lived on a farm at baseline were more likely to have parents with a lower educational attainment (81 percent vs 61 percent).
Farm living was inversely associated with symptoms of allergic rhinitis (3.9 percent vs 10.4 percent; p<0.001) and wheeze (7.9 percent vs 11.7 percent; p=0.02) at baseline.
‘Farm dust’ treatment
How farm environment may protect against atopic diseases may be related to the microbes circulating around farms and their effect on the body’s defences. In GABRIEL, nose samples from children with intense farm contact exhibited a richer microbiome. Meanwhile, samples from children with asthma showed lower alpha and beta microbiome diversity, and the dust samples from these children’s rooms had less diversity.
Several studies have provided evidence that the guts of infants raised on farms contain higher amounts of specific bacteria that reduce inflammatory processes. [Allergy 2017;72:109-119; J Allergy Clin Immunol 2017;139:826-834.e13; N Engl J Med 2011;364:701-709; J Allergy Clin Immunol 2021;148:669-678; Curr Opin Immunol 2021;72:215-220; Nat Med 2020;26:1766-1775]
“Therefore, dietary choices such as the consumption of unprocessed cow’s milk may contribute to the farm effect. Additionally, exposure to a highly diverse microbial environment on farms may influence the microbiome of the upper airways and the gut,” according to the investigators. [J Allergy Clin Immunol 2011;128:766-773.e4; Nat Med 2020;26:1766-1775; J Allergy Clin Immunol 2018;141:1212-1214; Curr Opin Immunol 2021;72:215-220]
“However, results of the PASTURE birth cohort study carried out among European farm and nonfarm children indicate that although early-life exposure to diverse bacterial components is protective, successful maturation of the gut microbiome is key to protect against respiratory allergies and asthma,” they noted. [Nat Med 2020;26:1766-177; Allergy 2017;72:109-119]
The results of the GABRIEL study have raised the possibility of developing a treatment that contains ‘farm dust’ to prevent the development of allergies in children who are not exposed to farm environment.
Funded by the Dutch Lung Foundation, an international consortium of researchers is investigating potential treatments to prevent asthma and allergies. The treatments will be based on farm dust and unprocessed milk. They expect to deliver a product by 2027. [https://www.theguardian.com/society/2022/sep/04/miracle-farm-dust-pill-could-prevent-childhood-allergies]