In trying to explain America’s rising rates of allergies and asthma, one of the common theories is that we’re just too clean. And that theory just got a boost by scientists studying traditional farming communities.
The Amish communities concentrated in America’s rust belt share many similarities with other traditionalist sects, including the Hutterites, a group of Anabaptists that live largely in Canada and in the northwestern United States. Both are Christian groups that eschew most modern technology and make much of their livelihood from farming. But they have a key difference: Amish families farm traditionally, using hand-held or livestock-powered tools, while Hutterites use modern farm implements.
And that appears to make a crucial difference to their health: While less than 10 percent of Amish schoolchildren have asthma and allergies, the prevalence in Hutterite children is over 20 and 30 percent respectively.
In a study published Wednesday in the New England Journal of Medicine, Carole Ober, a geneticist at the University of Chicago, and her colleagues conclude that dust from the farm fields might protect Amish children from asthma and allergies, while shelter from this exposure might leave Hutterite children vulnerable.
It’s support for the so-called hygiene hypothesis: the idea that a lack of early childhood exposure to a diversity of germs can keep the immune system underdeveloped and more likely to overreact to things that are harmless — resulting in allergies and asthma.
It’s almost as if the immune system is “bored,” says Anne Sperling, an immunologist at the University of Chicago and a colleague of Ober. “Kids who live in just a bit dirtier environments are actually more protected against asthma and allergies.”
The Hutterites and Amish actually have very similar ancestral backgrounds. They can trace their ancestors to Central European communities only about 15 miles apart, and they remain fairly genetically isolated from the rest of American society.
This genetic similarity gave Ober and her colleagues an opportunity to focus on lifestyle differences, the major one being farming practices. Both communities rely heavily on farming, but while the Amish use pre-industrial farming practices, like horse-pulled plows and hand sowed seeds, the Hutterites use modern tractors and milking machines. Traditional farming means the Amish have much more exposure to microbes in their farms — an exposure they pass on to their children when they come home from the fields. Ober’s team found almost seven times more diversity of microbial life in dust from Amish homes than dust from Hutterite homes.
The children’s blood told a story of diverging immune profiles as well. For example, Amish children had higher levels of white blood cells called neutrophils, while those cells had lower levels of three proteins known to play a role in inflammatory responses.
The researchers then took those dust extracts back to the lab. For a month they exposed mice to dust from each community before inducing asthma in the mice. In mice exposed to dust from Amish households, the asthmatic response was less severe, with airways contracting half as much as control mice. The Hutterite dust almost always had the opposite effect.
“This tells us something in the dust is protective,” said Sperling.
And when they engineered mice lacking genes important for immune system functioning, the protective effect was lost, providing even stronger evidence that the lack of allergies and asthma in Amish children is due to something unique about their immune systems, she said.
The findings are compelling, said Ober, but the scientists can’t rule out the possibility that an uncontrolled difference, like geography, could have influenced the results. (The Amish groups sampled lived in Indiana, while the Hutterites lived in South Dakota.) Ober is hoping to do a follow-up experiment in which Hutterites would expose their babies to more from their environment.
At this point the researchers are also unable to say what specific component of the dust might be protective.
“We have this grandmother sort of wisdom that [says], sure you need to go and get exposed to dirt and bacteria so you can grow healthy and protected,” said Talal Chatila, a pediatric researcher specializing in immunology at Boston Children’s Hospital, who was not involved in research. “The science is now moving to actually starting to define at the molecular level what are the components or factors that enable particular exposures to be protective against allergic diseases.”
While the idea of some sort of pill or spray that could kickstart our children’s immune systems remains in the realm of science fiction, the study reminds us that our children don’t have to live in completely sterilized environments, said Sperling.
“It might be important just to let them be kids and be outside … and play in the dirt,” she said. “All that might be important stimuli to develop an immune system that’s protective against asthma.”
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