Preventing allergies with The Country Life
This story on National Public Radio’s Morning Edition aired this week, describing a recent study which examined the apparent rise in childhood allergies, and the factors that might be contributing to this upswing. Allergists note that many allergies, such as those against common foods, appear to be two to five times more common than they were a generation ago. One potential hypothesis to explain this rise is the “Hygiene Hypothesis,” which states that these allergies have arisen because our bodies immune systems are not being challenged in the same manner that they were previously.
Longtime readers of the BIO230 files are almost certainly familiar with this hypothesis, in this article which detailed how the complexity of the intestinal flora was inversely correlated with the tendency to develop allergies, and this article which presented a novel approach to treating septic shock. There is a growing body of evidence that supports the contention that our fastidious lifestyle comes at a cost, in the development of many immunologically derived diseases.
The story on NPR detailed an epidemiological study examining an Amish community in Indiana, and their incidence of allergy symptoms. The authors examined children ages 6 to 12, and looked for symptoms of hay fever, asthma, or contact dermatitis, and this cohort was compared with a control group from a Swiss farming community that represented a genetically similar group. What was found was that the Amish cohort had statistically significantly lower levels of all of the allergy signs that were compared. Lifestyle factors associated with this decreased level of allergy included large family size (Amish families averaged 5.9 children), exposure to large farm animals (mainly cows), and consumption of raw or unpasteurized milk. Unfortunately, the low number of children in the Amish cohort (157) in comparison the the Swiss farming community (3006) means that the relative contribution of each of these lifestyle factors is difficult to determine. An expanded study, with the examination of additional exposure factors may help to shed light on the protective effects of the farming lifestyle.
So what is the basis of the biology underlying this observation? The Hygiene Hypothesis holds that chronic exposure to allergens (environmental triggers that can promote allergies) results in desensitization to the stimulus, resulting in loss of allergy symptoms. As our immune responses develop during early childhood, exposure to pathogens can promote responses that can give us lifelong resistance to many diseases. Exposure to innocuous pathogens (those that might not pose a significant risk to health) in early childhood can produce a very different result, where the immune system is essentially “turned off” to those non-harmful pathogens. This is actually a critical event, because many immune responses can actually result in damage to the human body if they occur in a chronic, or long term manner, and by turning these responses of our body off this adverse effect can be prevented. It has been proposed that because our diet is rich in processed foods, and our homes are clean, that we are no longer exposed to the variety of immunologic challenges today that we were a generation ago. Consequently, the immune systems of today’s youth do not develop this desensitization phenomenon, and environmental allergies could be the result.
Comprehensive analysis of whether the Hygiene Hypothesis is real or not does not lead to a clear answer. What is apparent is that exposure to certain allergens in early childhood does appear to promote a reduction in allergies, whereas exposure to different allergens has the opposite effect. The timing of exposure is also critical, however there are also significant genetic contributions by the individual. All of these facets drive home the point that the interaction between our immune system and the environment is incredibly complex, and will be difficult to unravel!