When government officials hear the words "backyard livestock," they tend to worry about disease outbreaks and sanitation crises. And for good reason, as improperly managed animals — including dogs and cats — can be the source of all sorts of public health problems. When it comes to asthma, however, recent science is hinting that early childhood exposure to domestic animals can actually protect against the chronic condition, so well-cared-for backyard animals like chickens or miniature goats could actually have an additional, unexpected benefit.
I learned about this intriguing idea on Quest, a science program produced by KQED in San Francisco (with all programs available for on-line viewing). One of the segments is all about asthma: what it does, how to prevent it, and why the incidence has been rising rapidly in recent years (they state that rates more than doubled in small children in the U.S. between 1980 and 1994). Asthma's underlying cause and triggers are still a mystery — as yet, no one has found the "magic allergen" or markers of genetic predisposition — and so researchers are looking at diet, stress, air pollution, early exposure to allergens and more. (For more information, consult a series of papers in Environmental Health Perspectives examined how the environmental influences asthma, and a recent study from the Health Effects Insitute found a causal relationship between traffic-related air pollution and exacerbation of asthma in children.)
One thing that stands out is that asthma rates have been rising in industrialized societies like the U.S., Western Europe, Australia and Japan. And one thing that these places have in common is more time spent inside, more concrete, more cars, fewer farms, and less exposure to the natural world.
This leads us to one of the intriguing ideas about asthma and other allergies (and even diseases related to chronic inflammation, as New Scientist reports): the "hygiene hypothesis." This hypothesis, first proposed a few decades ago, suggests that as our environments become cleaner and we spend less time around "dirty" things like animals and the natural world, our bodies aren't being exposed to enough microorganisms and therefore don't develop the proper defenses (or, in the case of asthma, don't overreact to external allergens).
The program mentions a study of children in Germany, Switzerland and Austria that supports the hypothesis. In rural communities, researchers found lower asthma rates in children whose sleeping quarters were close to the livestock stables than those who lived in town, away from the animals. One possible explanation for the difference is that exposure to the microbes found in manure and stables protects a child from developing asthma by causing favorable changes to their immune system. (Although the exact study is not mentioned in the Quest piece, I suspect it is one in the New England Journal of Medicine that concludes "Endotoxin levels in samples of dust from the child's mattress were inversely related to the occurrence of hay fever, atopic asthma, and atopic sensitization.")
The hygiene hypothesis and its connection to livestock are still only hypothetical at this time — there are a number of confounding results, like higher asthma rates among low-income children in allergen-laden urban areas and the link between asthma and exposure to tobacco smoke at a very early age. If it turns out that early exposure to livestock reduces the chance of developing asthma, it could be a benefit above and beyond the urban farming's main benefits of good, clean and local food.
Editor's note: Robyn O'Brien's fantastic 2009 book, "The Unhealthy Truth: How Our Food Is Making Us Sick - And What We Can Do About It," offers an alternative to the hygiene hypothesis when it comes to asthma. (Alas, "The Unhealthy Truth" is one of many sitting in a teetering pile Ethicurean headquarters that got read and should have been reviewed by now … and that we continue to hope will someday still be.) O'Brien talks to Harvard Medical School pediatrician David Ludwig, author of "Ending the Food Fight: Guide Your Child to a Healthy Weight in a Fast Food/ Fake Food World," who believes that it is the U.S. dietary shift toward fake food that has sabotaged our immune systems, both by subjecting us to an onslaught of evolutionarily-novel compounds in the form of artificial and/or genetically modified ingredients, and by depriving us of the essential nutrients to mount a defense. In this fake-food hypothesis, farm kids and those whose parents keep urban livestock would have lower asthma and food-allergy rates because they grow up in a family food culture less dependent on processed food.
Photoillustration: Livestock breeds image created by W. Layman in 1911, archived at Michigan State University Museum.