Children growing up on farms are less likely to develop allergies and asthma. Farming has been part of human culture for probably 7000 years.
It is widely accepted now that a symbiotic relationship with a diverse population of microbes in the environment, on the skin, in the gut and in the lung is necessary for a healthy immune system (“microbiome“). These microbes influence the balance between inflammation and immune tolerance. That relationship needs to be developed in early life, and nutrition is a major part.
Big European cross sectional studies – PARSIFAL and GABRIEL. Amish and Hutterites in US are genetically similar but Hutterites use industrial rather than traditional farming techniques (and have 4-6x the rate of hay fever and atopic sensitization).
Prenatal maternal exposure to farm animals is protective against eczema in the first 2 years of life, and against asthma symptoms pre-school.
Farm milk consumption in the first year of life is protective against respiratory allergies. Not clear what it is about it – more whey? Higher levels of cytokines or polyunsaturated fatty acids?
In children, exposure to cows and hay was protective against asthma. Some evidence for pigs, but risk seems to go up for sheep.
Mediators thought to potentially be N-gylcolylneuraminic acid (animals/pets) and arabinogalactan (plants).
Lipopolysaccharide (endotoxin) is widespread in the farm environment. Levels in mattresses inversely associated with hay fever, atopic sensitisation and asthma.
Lack of gut microbial diversity in first month of life predicts school age asthma.
Dietary diversity in first 2 years of life protects against asthma and allergic rhinitis. The link between gut microbes and lung health is thought to be short chain fatty acids, such as acetate and butyrate.[Ped Allergy and Imm 2022]