Dr. Andy

Reflections on medicine and biology among other things

Friday, May 27, 2005

Allergic Disease on the rise

Two good studies in the May 21 British Medical Journal (catching up on our reading, are we? ed Sort of, I've been trying to flag particularly pertinent articles when downloading and read them first) about the increasing prevalence of allergic disease.

It is well established that allergic diseases (eczema, food allergy, allergic rhinitis, and asthma) have increased in prevalance over the last 40 years or so. Some of this may be due to better recognition and diagnosis, but some is almost certainly due to a true increase in prevalance. There has been some data in Europe, that at least for asthma, the rise in cases has stopped and numbers may even be coming down.

The reason for the overall increase is still unclear. The leading theory is the so-called "hygeine hypothesis" which postulates that less exposure to dirt and bacteria predisposes to allergy. While this hypothesis has some good evidence for it (decreased allergic disease in farmers, for example) it also has some weaknesses (e.g. why is asthma epidemic in the American inner city).

The first article, by Latvala et al, measures asthma in young Finnish men, almost all of whom get physicals at age 18-19 as part of compulsory military service. This study showed that the number of men with asthma (and allergic rhinitis) continued to increase throught 2003, the last year studied.

The number of men with "disabling asthma" decreased significantly, however, almost certainly due to the availability of better treatments, like inhaled corticosteroids.

An even cooler study in the same issue, by Law et al., used stored blood samples from a British hospital to see if the incidence of atopy (basically allergy to specific things) had increased. They looked at the blood samples of men presenting for physical exams from three periods, 1975-6, 1981-2, and 1996-8. The prevalence of positive tests for allergy The percentage showing any allergy rose by >1/3 and for specific allergens like cat and tree the prevalence more than doubled.

One potential objection they didn’t address was that the prevalence of specific antigens may vary over time. Perhaps more people have cats now, or different trees are more common. I doubt that would explain much of the difference, however.

In summary, more and more evidence shows that allergies and allergic disease are getting worse. What a great time to be an allergist.


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