Childhood exposure to farm animals seems to help those with asthma
(HealthDay News) – Slightly distorting an old adage: It may be a good idea to keep 'em on the farm before they see the big city."
A number of studies have shown that growing up on a farm may protect children from getting allergies and asthma.
Allergic symptoms were lower among those youths who lived on a farm when a 2003 survey was taken, or they had lived on a farm previously, according to Helen Dimich-Ward, an associate professor at the University of British Columbia in Vancouver .
Canadian researchers surveyed 1,158 4-H Club members, aged 8 to 20, asking about current and previous residences and residential exposure to livestock, as well as any problems with allergies and asthma.
The highest prevalence of allergic symptoms was found in urban or rural residents without livestock. Diagnosed asthma was lowest among those who currently lived on a farm, while past farm dwellers had the lowest prevalence of ever having wheezing.
Like other researchers, Dimich-Ward said the "protective farm factor" may be the reason -- that is, kids who grow up on farms are less likely to suffer asthma and allergies because they have more frequent, higher exposures to endotoxins. Endotoxins, a piece of the bacterial cell wall, are generally found at higher levels on farms. They are present in livestock feces, barn and house dust and mattresses, researchers have found.
Researchers also call this the hygiene hypothesis -- that high levels of these endotoxins early in life toughen up the immune system and the child does not tend to get allergies or asthma. But exposure to high endotoxin levels in someone who already has asthma or allergies can aggravate the condition.
"Endotoxin exposure is an appealing explanation," Dimich-Ward said. That's true, she added, both for reduced allergic symptoms among farm children and for the results of some studies that found fewer allergic conditions for children exposed to dogs or cats at an early age.
However, she said, it is not yet absolutely clear that endotoxins are the protective mechanism. And it was not just having contact with farm animals in her study that appeared to have a protective effect.
"Rather, lower risks for allergic symptoms were associated with living on a farm or rural area and having livestock currently and at an early age," she said.
Dimich-Ward's findings echo those of earlier research. In a study published last year in the New England Journal of Medicine , researchers who evaluated more than 800 Swiss, German and Austrian children found asthma and allergy rates lower among the 319 who grew up on farms.
And a study published in the American Journal of Respiratory and Critical Care Medicine in 2000 found that a lower prevalence of asthma persists in farm children even after accounting for the fact that they smoke less than their urban counterparts.
>Every year, more than 50 million Americans suffer from allergic diseases, according to the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health.Dimich-Ward points out other factors may explain the finding. One possibility is that children who live on a farm may have parents who are not allergic, suggesting that families who may be prone to allergies would leave the farm environment. Relatively few parents of the farm children she surveyed had a history of allergies, she notes.
Another expert in the field calls the new research an interesting part of the puzzle, but agrees with Dimich-Ward that more research is needed.
"What's really needed is a longitudinal study going from birth," said Dr. Alex Marotta, a fellow at the National Jewish Medical and Research Center in Denver who has researched the topic.
Whether endotoxins are truly the reason these children on the farm have fewer asthma and allergy problems remains to be proven, he added.
Meanwhile, there's not much urban parents can do, he said.
What about buying a cat or a dog to boost endotoxin exposure? "That needs to be studied more," he said. One thing is known, he added: "Once you have developed asthma and allergies, having a cat in the house is bad."
On the Web
To find out more about kids and asthma, see the American Academy of Allergy, Asthma & Immunology.
SOURCES:
Helen Dimich-Ward, Ph.D., associate professor, respiratory division, University of British Columbia, Department of Medicine, Vancouver; Alex Marotta, M.D., fellow, asthma researcher, National Jewish Medical and Research Center, Denver; May 18, 2003, presentation, American Thoracic Society, Seattle
Author:
Kathy Doheny, HealthDay Reporter
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