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May 10, 2006

Source of Allergies - still a huge unknown

Allergies, it seems, make for an all-purpose marker for societal ills. Even our growing girths have been implicated. The exact nature of the connection is up for debate, but, according to Javed Sheikh, the clinical director of allergy at Beth Israel Hospital, "obesity and asthma clearly seem to be linked."

Still, while the rise of allergies may indeed be the product of pollution, poverty, and sloth, it might also have very little to do with any of these. Slimmer Americans breathing cleaner air might still have reason to dread the spring.

One of the more widely accepted explanations for the rise in allergies is something called the "hygiene hypothesis." By killing off so many of the microbes and parasites that used to prey on us, the hypothesis suggests, we've thrown our immune system off balance. "We've more or less taken away an important function of the immune system," says Hamilos. "It tends to look for other things to do, and it looks to things that aren't very productive, namely attacking allergens."

Instead of focusing the blame on damage we've done to the environment, the hygiene hypothesis sees allergies more as an unintended consequence of our fight against more debilitating diseases. "We want to live longer and better," says Andrew Saxon, a leading allergy researcher at UCLA Medical School, "and the price is allergy."

As proof, researchers point out that allergy rates in poor countries--where diseases long since eradicated in the developed world still run rampant--are correspondingly lower, even in polluted urban centers. Some, like Sheikh, emphasize the role of a compound called endotoxin, produced by E. coli and other bacteria common in animal feces. Studies have found that children who grow up on farms (around microbial havens like untreated ground water, dirt, and manure) are less likely than their urban counterparts to develop allergies. Others look to intestinal worms, citing studies that show an increase in allergy rates among children given deworming medication.

In a related vein, some research has suggested that early exposure to an allergenic substance may actually protect one from developing allergies. As-yet-unpublished results from a study led by Gideon Lack, an allergist at London's St. Thomas' Hospital, suggest that, in countries where babies have a peanut-heavy diet, peanut allergy rates are a fraction of those in countries like England and the US where babies are not fed peanuts--out of a fear they'll prove fatally allergic. To see whether peanut exposure is actually decisive, in July Lack will begin a seven-year study, funded by the National Institutes of Health, in which hundreds of English infants will (under medical supervision) be fed peanuts on a regular basis, tracked to see what sort of allergies they develop, and compared with a peanut-free control group.

Similarly, work by Dennis Ownby, head of Allergy and Immunology at the Medical College of Georgia, has shown that being born into a home with multiple pets decreases dramatically one's odds of developing allergies of any sort.

As of yet, no doctor is suggesting that parents put their babies on a peanut diet or have them play in manure. But there have been attempts to figure out how to recreate certain antiallergenic aspects of the pre-modern lifestyle, what Sheikh calls "the particular dirty profile that leads to protection against allergy." Joel Weinstock, for example, head of Tufts New England Medical Center's gastroenterology division, has speculated that one possible cure for allergies might be a dose of a relatively benign parasite called the pig whipworm.

In the meantime, allergies will remain, as George Beard believed more than a hundred years ago, a disease of modern living--a disease of poverty, pollution, development, and cleanliness. In other words, an epidemiological Rorschach.

source: Boston Globe Online

Posted by David at May 10, 2006 8:02 PM