Growing up on a farm is good for the microbiota and may also help protect against allergies

Growing up on a farm promotes exposure to a variety of microorganisms, which is beneficial for the development of a young child’s gut microbiota and may help prevent certain allergies. This article reviews the available scientific evidence.

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Many advances in modern microbiology have been based on the analysis of microorganisms that are pathogenic to animals and humans. Undoubtedly, these advances have greatly contributed to reducing maternal and infant mortality and increasing life expectancy worldwide. However, we should not forget that, from the very beginnings of this science, before turning to pathogenic organisms that pose a threat to public health, Louis Pasteur had initially focused on “good microbes”—those involved in the fermentation processes essential to the production of wine and beer.  

Microorganisms Found in Soil, Oceans, and Animals

Pathogenic microorganisms are in fact only a tiny fraction of the microbial world: bacteria, viruses, parasites, and microscopic fungi—microorganisms are everywhere. And they are often indispensable: in the soil, where they form symbiotic relationships with plant roots; at the bottom of the oceans, where they develop unique forms of life under extreme conditions; and in animals, including humans. In this case, we’re talking about the “flora,” as it was once called, or the “microbiota,” as it’s known today, found in the oral cavity, the respiratory tract, the gut, the vagina, the skin… Every day, we discover new connections between these microbiotas—and particularly the gut microbiota—and the immune system, general and hormonal metabolism, and even the brain.  

Rising Allergy Rates: What’s the Link to the Microbiota?

The ^19th and 20th centuries were marked in Western countries by significant societal changes, including increasing urbanization, hygiene—still viewed as progress—and the gradual loss of contact with a traditional rural environment based on agriculture and livestock farming. This phenomenon has accelerated and become global since the 1950s, and a renewed interest in the functions of the human microbiota in the late 1990s coincided with some somewhat surprising epidemiological observations : an increase in the prevalence of diseases that were previously quite rare, such as allergies , autoimmune diseases , and inflammatory bowel diseases . Research into the causes of the unprecedented rise in so-called “atopic” allergies (asthma, allergic rhinitis including hay fever, atopic dermatitis, and certain forms of food allergies) is emblematic of a scientific approach. It begins with epidemiological observations : nearly 5% of allergic diseases in European countries in the late 1940s, nearly 40% in the 1990s–2000s… Next, it analyzes these findings using “cross-sectional” studies that compare populations with varying levels of exposure across the globe. Finally, it confirms the results through long-term cohort studies, which also help elucidate the underlying mechanisms.  

The Limitations of the “Hygiene Hypothesis”

The rise in allergic diseases in so-called “developed” countries was initially attributed to urban pollution, and most research focused on this explanation. There is indeed a correlation between the severity of respiratory allergy symptoms (rhinitis and asthma) and pollution. But pollution is not the cause of the increase in the number of people with allergies within a population. Rather than a harmful effect of city life, could it not be the loss of protective factors associated with country life—the loss of a certain traditional rural lifestyle? As early as the 1^9th century, an English doctor noted that the few children with hay fever in rural areas were not the children of farmers—who were most exposed to hay—but those of the village landowners under his care! A disease of the wealthy! In the 1990s, the hypothesis that reduced exposure to microbes explained the rise in allergies gained traction based on observations of allergic children who shared this reduced exposure: birth by C-section, mothers treated with antibiotics during pregnancy, only children, families of high socioeconomic status, frequent antibiotic treatments, and no attendance at daycare centers… Thus was born the so-called “hygiene hypothesis,” conceptualized by the English allergist David P. Strachan. Could advances in hygiene, then, be responsible for the rise in allergic diseases in the second half of the 19th century? Studies conducted in rural areas of the mid-Alpine mountains by a group of researchers—and confirmed by other studies in different countries—quickly showed that the “hygiene hypothesis” was oversimplified. In fact, these researchers observed that there were far fewer cases of allergies among children living on farms whose parents were themselves the children of farmers. They also showed that children who had consumed raw milk during early childhood—and whose mothers had consumed raw milk during pregnancy—were equally “protected” against the development of allergic diseases, regardless of whether they lived on a farm. This finding was unexpected—and somewhat unsettling—as it contradicted efforts to control pathogenicity through milk pasteurization and government recommendations regarding “raw milk” dairy products…

Research to Confirm the Findings

The desire to validate these results through rigorous methodology led to the creation of the European “Pasture” cohort, which compared—beginning in the third trimester of their mothers’ pregnancies and continuing for eighteen years— 500 German, Austrian, Finnish, French, and Swiss children living on livestock farms with 500 children from the same rural backgrounds but not living on farms. Its results fully confirm those of “population-based” studies and provide numerous additional insights. Life on a farm and contact with animals do indeed “protect” against the onset of allergic reactions during childhood, and this effect is even stronger when the mother herself has lived on a farm, spent time in the barn and stable, and been in contact with a wide variety of animals. However, it is important to distinguish between different types of livestock operations and farms that are more or less conducive to promoting microbial diversity: intensive farming or small-scale farming, animals treated or untreated with antibiotics, use or non-use of pesticides, etc. Apart from life on the farm, the consumption of raw milk and “farm-fresh” dairy products (“farm-fresh”) such as butter, yogurt, and cheese also offer protective benefits, as does the consumption—starting with the introduction of solid foods (which itself is “protective” when introduced early)—of a wide variety of cheeses. In France, health authorities recommend that young children—particularly those under 5 years of age—pregnant women, and immunocompromised individuals avoid consuming raw milk or raw-milk cheeses, with the exception of “hard, pressed” cheeses such as Comté, Beaufort, Gruyère, and Emmental, which are made by heating the milk and undergoing a long aging process (editor’s note). Regardless of the protective factor considered, it is the diversity of microbial exposures—rather than their quantity—that is associated with protection. This protection against allergies is associated with a specific orientation of the immune system, striking a balance between defense against pathogenic microbes (the study showed that consuming raw milk also protected against infections during children’s first year of life) and tolerance toward nonpathogenic microbes and dietary proteins.  

Maturation of the gut microbiota in young children

This orientation of the immune system is conferred on the child as early as fetal life, due to the mother’s environmental exposures, and reinforced by the child’s own exposures during the first four years of life. It is linked to optimal maturation of the gut microbiota during the first year of life. The fact that the development of the immune system depends on the gut microbiota is not a recent discovery… but it may have been easily overlooked, given that microbes are often associated with “dirt” and the microbiota with intestinal functions considered rather unseemly!

Cheese: A Source of Microbial Biodiversity

Discoveries in the field of allergies are restoring the notion that gut microbiota are inseparable from our survival . The consequences of an imbalance in the gut microbiota on the onset of conditions such as obesity or depression are now being studied. There is strong evidence supporting its role in chronic inflammatory diseases, through a mechanism similar to that involved in allergies. Meanwhile, in today’s European diet—where the proportion of fermented foods has greatly decreased—cheeses remain the primary sources of microbial biodiversity, as highlighted in the White Paper “Health Benefits and Risks of Cheese Consumption,” which synthesizes the most recent scientific findings. The role of nonpathogenic microorganisms in the development of the immune system and the prevention of “diseases of modernity,” including allergies, is yet another reason to preserve microbial biodiversity . This can only encourage the search for solutions—inspired by research findings—to maintain sufficient exposure to this biodiversity, whether environmental or nutritional, particularly among children in their early years of life. Dominique Angèle Vuitton , Professor Emerita of Clinical Immunology; University of Franche-Comté, University of Franche-Comté This article is republished from The Conversation under a Creative Commons license. Read the original article.