Asthma is a complex, chronic lung problem that now affects nearly 10 percent of all children. Both the incidence of new cases and the prevalence of ongoing cases in the pediatric population have been rising steadily for years, although there are hints these increases may have leveled off.
A wealth of research suggests a huge part of asthma causation comes from the environment the child lives in, things like air quality and exposure to various agents. Some children have clear-cut allergies as a contributing factor, but the majority don’t. Genetic factors also play a role, probably because the way the lung responds to these various things is a tendency we inherit. Exactly what might be triggering the rise in asthma has been debated for many years. Candidate causes include a more sedentary lifestyle in children, increasing childhood obesity, and increasing urbanization of our country. A century ago most people lived on farms; now most don’t.
This possibility is the subject of a recently published and fascinating study in the New England Journal of Medicine. The authors were curious about asthma rates and causation in children who live in the traditional, rural setting typical many years ago. There are some data children raised on traditional dairy farms with early exposure to farm animals have a reduced risk of asthma. The investigators used a clever comparison between two groups of children: Amish children in Indiana and Hutterite children in South Dakota. Both of these are religious groups descended from seventeenth-century Pietistic sects originating in Europe.
I have had many Amish patients in my career, but not any Hutterites. They are similar in lifestyle, but there are some key differences that the authors of the study used to get at studying asthma. The Amish are predominately farmers, although I have known many who are not. Amish farming practice is straight out of the 19th century. They use no power machinery. They use horses to plow; they manure their fields as their great-great grandparents did, and they use horse-drawn implements to harvest their crops. If they have dairy cows, they milk them by hand into a bucket.
The religious practices of Hutterites are very close to those of the Amish, but their farming practices definitely are not. The Hutterites live communally and use modern machinery on highly industrialized modern farms. The comparison between the two groups is useful because in other respects they have very similar lifestyles in things believed to be important for asthma risk. These include large families, minimal exposure to urban air, prolonged breastfeeding, no indoor pets, minimal exposure to tobacco smoke, and low rates of obesity. They also have very similar diets and similar genetic backgrounds. Going into the study, the authors already knew the prevalence of asthma for Hutterite children was 21 percent (a high rate) versus only 5 percent in Amish children. Why the difference?
The investigators measured many things, but key among them were studies on dust samples collected from the children’s environments. They analyzed the microbial makeup of these samples, as well as used them to challenge the lungs of mice in an experimental asthma model. They also looked at several markers of immune function in the blood cells of the two groups of children. What did they find?
The results are a bit complicated, and if you want the details look at the article. There’s also a good editorial accompanying it. The bottom line is that the innate immune response of the Amish children was profoundly different from that of the Hutterite children, and this difference appeared to be shaped by exposure to very different microbial agents in the environment as measured in the dust samples. More than that, the dust samples from the Amish farms actually protected the mice in the animal model from an asthma attack. That’s amazing.
Maybe we should be treating asthma with Amish farm dust? I’m not serious, of course, but the study does suggest some reasons why the change from a traditional farming way of life to the way we live now may be part of why asthma is now so common. Early and sustained exposure to certain microbes may be a good thing, a notion that was proposed many years ago — the so-called hygiene hypothesis.
Christopher Johnson is a pediatric intensive care physician and author of Keeping Your Kids Out of the Emergency Room: A Guide to Childhood Injuries and Illnesses, Your Critically Ill Child: Life and Death Choices Parents Must Face, How to Talk to Your Child’s Doctor: A Handbook for Parents, and How Your Child Heals: An Inside Look At Common Childhood Ailments. He blogs at his self-titled site, Christopher Johnson, MD.
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