Monday, September 21, 2009

Regional Differences in Food Allergies

I came across a story in New Scientist magazine about possible reasons why people in different parts of the world are prone to different food allergies (“Food Allergies Get Curiouser and Curiouser.”) The peanut is a common allergen in the United States, but not so common in other countries. Melon is a more common problem in Greece. Apples are the culprit in Italy.

Why are there so many regional differences?

This article discusses studies that show a possible reason: many plant pollens that cause hay fever contain proteins that are very similar to the proteins in certain foods. While the plants and foods aren’t actually related, the molecular structure of the proteins are similar enough that a sensitivity to one (in the form of hay fever) might “prime the pump” and make you more susceptible to developing an allergy to the other. The article uses the examples of birch pollen allergies, which may make northern Europeans more prone to apple allergies, dust-mite feces that may correlate to shrimp allergies, and mugwort allergies that may link to carrots, celery, and sunflower seeds.

There have been studies in the past that have tried to examine reasons why regional differences exist in food allergies. In November 2008, I wrote about a study published in the Journal of Allergy and Clinical Immunology that compared Jewish populations in the U.K. and Israel and their very different rates of peanut allergy. The study used Jewish populations in both regions to try to control as many cultural variables as possible. Their conclusion was that since the Israeli population gives infants more peanuts and has a lower rate of peanut allergy, perhaps everyone should introduce peanuts to infants earlier and in larger quantities. But that goes contrary to other studies that seem to show it’s better to prevent peanuts from being introduced until later in life.

But the study didn’t seem to take into account environmental pollens in the two countries, which would be vastly different between the two climates. The New Scientist article brings up an interesting new angle on that older study – what if the reason the U.K. children have more peanut allergies is because their bodies are already primed to react by a pollen that is prevalent in the U.K., but which doesn’t exist in the drier environs of Israel? It would be interesting if someone could go back to those original U.K. and Israeli populations and cross-check the existing pollens in those two areas to see if a new pattern emerges from that.

So once again, we still don’t know very much about the causes of food allergies. We are still bombarded by theories. We still feel like we’re grasping at straws. However, there is some good news: more and more studies ARE being conducted. Only after many years and many individual studies that test different aspects of allergies will scientists be able to look back, gather up all the thousands of puzzle pieces from all those studies, and begin fitting them together into a whole picture. And only then will we start to see what we’re really facing and how to deal with it all.

On the one hand, it’s frustrating to feel like we still know so little. On the other hand, I have to remind myself that we know a lot more now than we did a decade ago, and in ten more years, we’ll know even more. Each new study turns over another puzzle piece on our table. And that gives me something to hope for.

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