WEDNESDAY, Sept. 18, 2002 (HealthDayNews) -- Farm living may be hard work, but the payoff is not just toughened hands and sinew: Kids who grow up around barns and stock are much less likely than other children to suffer allergies and asthma, new research shows.
The European study, appearing in tomorrow's issue of The New England Journal of Medicine, offers strong support for the "hygiene hypothesis." This theory states that as developed nations become cleaner -- reducing childhood infections that toughen the immune system -- their citizens become more vulnerable to allergies.
In this model, the chief agent of irritation is endotoxin, a term for the fatty proteins that make up the outer shells of bacteria in animal feces. Contact with endotoxin at key points in the development of the immune system primes the body's defenses enough so that future meetings with the proteins don't spark allergic reactions.
With their hideous filth, cities were once a major source of endotoxin. However, that changed thanks to improvements in sewage, plumbing and other mercies of modernity.
Farms that support stock have always been rife with bacteria. So they offer researchers a ready test bed for the hygiene hypothesis. If kids living on farms are exposed to more endotoxin -- which physician-author Lewis Thomas once called one of "Nature's darkest secrets" -- they should have fewer allergy problems than those raised in homes with less of the stuff around.
Led by Dr. Charlotte Braun-Fahrländer, the researchers compared asthma and allergy rates and endotoxin exposure in 812 Swiss, German and Austrian children, aged 6 to 13, growing up in rural communities. Of those, 319 were raised on farms.
Braun-Fahrländer interviewed parents about their child's history of asthma and hay fever. They also took blood samples from the boys and girls to look for immune system activity. Last but not least, they vacuumed their mattresses to measure how much endotoxin they encountered every day.
The level of endotoxin in bedding was higher on the farm, and children exposed to more endotoxin at home were less likely to have hay fever and asthma, the researchers found. Blood tests showed that contact with more endotoxin was tied to muted production of immune molecules called cytokines, which help trigger inflammatory responses.
The results suggest that "environmental exposure to endotoxin may have a crucial role in the development of tolerance to ubiquitous allergens."
Dr. Andy Liu, an allergy expert at Denver's National Jewish Medical and Research Center, calls the new research "a nice piece of work" that begs for additional studies. The most important of these, Liu says, would be following children from birth to see who develops allergies and what irritants they were exposed to rather than asking their parents years later about their contact with potential allergens.
Liu says these farms are rich in endotoxin. His own research has shown that concentrations of endotoxin in barn dust are as much as 50,000 times higher than they are in dust from cities. Barns are also far dustier than homes, increasing the volume of exposures.
Another factor of farm life, Liu says, is exposure to endotoxin in unpasteurized dairy products, such as raw milk. In an earlier study, some members of the European research team showed that babies whose mothers had fed them unpasteurized milk had remarkably low rates of asthma as children.
While the latest study bolsters the hygiene hypothesis, it leaves several questions unanswered. Some exposure to endotoxin appears protective, yet many people suffer from contact with very high levels of germ protein. So there seems to be a middle ground that's beneficial, Liu says, but scientists haven't yet found it. "That's still kind of out there, in terms of how much is too much," he says.
Dr. Scott Weiss, an immunologist at Harvard Medical School in Boston, agrees the study "tends to support the hygiene hypothesis, but it doesn't move us in the direction of any kind of clinical cure or treatment." No one is going to feed dirt to a baby or put their crib in a barn to shield them from allergies later in life.
Nor, adds Weiss, author of an editorial accompanying the journal article, does the work prove that endotoxin -- and not some other aspect of farm life -- is protecting children. "I think it would be wrong to say that endotoxin exposure explains everything that's protective about farm life," Weiss says.
What To Do
For more on allergies, try the American Academy of Allergy, Asthma and Immunology. And for a look at how allergens trigger an immune reaction, check out HowStuffWorks.
