Can early exposure to nature be useful for allergies?

With an open mind I have been following David Suzuki’s latest campaign to encourage people to be spend more time outdoors with some evidence showing benefits to health in general. In his work, Suzuki highlights some studies showing an increased sense of wellbeing, decreased blood pressure, and other health benefits with increased out door activities.

I have no doubt that there are health benefits from spending more time with nature. Just the act of getting out of the house to engage in mild to moderate exercise outdoors may be helpful for the mind and body.

I then began to ponder if there are any theoretical benefits to being regularly exposed to the great outdoors in terms of allergies. There isn’t a whole lot of evidence based research on this, so I am speaking in this blog about some theoretical benefits made from what is currently known, extrapolating from other studies.

When someone develops an allergy to something, it is possible that they can eventually (if they’re lucky) develop immunologic tolerance to whatever it is that they are allergic to with repeated exposure. This concept is called anergy in immunology. Anergy is the basis of allergy immunotherapy wherein controlled escalating dose exposures can try to desensitize, aka re-train the immune system of a person to no longer react as if the harmless pollen is a parasite.

While the technique for aeroallergen desensitization through allergy immunotherapy works very well for inhalant allergies such as tree, grass, ragweed, dust mite, etc., the risks associated with food allergy desensitization are still, in my view, too high risk as many patients will experience anaphylaxis during the desensitization process. They are working on making this safer as we speak. The Cochrane Review, which is an independent body that evaluates scientific evidence behind medical interventions, gives allergen immunotherapy a class IA recommendation for asthma and a class IB recommendation for rhinitis which are the highest and second highest possible recommendations a medical intervention can receive. Immunotherapy has a 100 + year track record of safety and efficacy. Essentially, this is a method of retraining the immune system to stop reacting to the allergen as a harmful parasite.

While many clinical trials have shown that desensitization therapy is possible with just about any type of allergic sensitization including food, medications, and airborne allergens (provided it was a true allergy to begin with), I am reminded of the many patients who have tried this on their own using products such as unfiltered unpasteurized honey who have had anaphylaxis (life threatening allergic reactions). Do not attempt to desensitize yourself at home! There is a reason why I have over 13 years of training in my field!

Getting back on track, how does all this relate to early exposure to nature? When I examine the natural peaks and troughs of pollen counts outdoors, I cannot help but notice that the pollen levels naturally rise and fall. A form of allergen immunotherapy that is commonly done by an allergist is called “pre-seasonal allergen immunotherapy”. This is when a licensed medical specialist in allergies will inject you weekly with the pollens you are allergic to, with each subsequent dose being a higher dose than the previous. This has been proven to “retrain” the immune system in most patients with allergies. For example, if you have a birch tree pollen allergy, I would be injecting you with controlled doses of birch allergen before the tree season and try to “retrain” your immune system to no longer see the pollen as a foreign harmful invader by your body.

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Given that pollen counts gradually rise and peak, it is possible that if you spent every day in nature from the beginning to end of pollen season you may be able to get a similar gradual retraining of the immune system.

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This is where the evidence gets a little gray and I have to extrapolate from other studies and the collective clinical experience of “medical expert opinion”, which is actually a lower form of evidence.

In children, it generally takes 2-3 repeated seasons of exposure to develop seasonal allergies. New immigrants who come from a different part of the world where they did not have a chance to grow up with the same types of trees, grasses, and weeds will often exhibit this same 2-3 year cycle (i.e. their allergies begin to manifest after 3 years of being in their newly adopted country).

Now here is the other tricky part. Immune system “retraining” tends to work better the younger you are. There are many reasons, known and unknown, for why this is the case. One of the reasons is that the main training center organ where some parts of the immune system go to get their education, called the thymus, gets smaller as we age. The smaller the “university” for our immune system the less “retraining” that can occur. As such, there is solid randomized placebo controlled evidence demonstrating that receiving allergen immunotherapy in youth is truly disease modifying. For example, a robust trial of aeroallergen immunotherapy in children showed that using allergy immunotherapy in childhood can actually prevent the development of asthma.

People can also lose the tolerance they have already developed for their immune system without exposure. In children with peanut allergy for example, a child who outgrows their peanut allergy can actually re-acquire their allergy if they avoid that food for a long time. In fact, this is the very danger of going to a non board certified clinical immunologist and allergist who may not be aware of this nuance and suggest that you in fact avoid things based simply on skin prick testing results being positive. A person can actually lose their established tolerance and have symptoms from losing their anergic state by unnecessary avoidance! ALWAYS seek guidance about allergies from a board certified clinical immunologist and allergist.

Another common scenario that I see often in clinical practice is someone moving out of their parents’ house where they grew up with a cat and/or dog and returning to that house after a prolonged absence (say in University). When they return, they start to notice allergic symptoms around the cat and dog where previously they didn’t have symptoms. This is a real life demonstration of losing anergy.

It is possible that the immune system can reacquire tolerance on its own as no one fully understands how this occurs. However very few people are able to do this. It is also possible to reacquire the tolerance using allergen immunotherapy in a controlled, methodical, and safe way.

I digress, going back to the topic at hand. With exposure daily to nature I wondered if it is possible to have the same retraining effects on the immune system naturally as the pollen exposures “naturally” gradually increase to a peak. This would necessitate near daily exposure however to the outdoors which is difficult in modern society with our busy work schedules and commitments. Studies done with a placebo controlled arm for allergen immunotherapy do in fact show that some patients get some of the possible “retraining” changes in the placebo arms during pollen seasons suggesting that this idea is at least plausible.

New methods such as sublingual tablet immunotherapy (getting the pollens in a controlled tablet form) are now available that try to mitigate the risk of oral desensitization. While all forms of allergen immunotherapy have some risk, it does appear that tablet immunotherapy offers a safe and effective option for patients.

So I’ll throw the question out there – is it possible that not enough early and frequent childhood exposure to nature or the outdoors is increasing the prevalence of allergies that affect the nose, eyes, and lungs? Are we keeping our children indoors too much?

In conclusion, I cannot make any specific recommendations to your particular case for obvious medical legal reasons over this blog, but I do wonder if there are benefits in the field of allergies by being more in touch with nature.

Dr. Jason K Lee

Twitter @lee_jasonk
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