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December 18, 2005

BehindTheMedspeak: Why has peanut allergy become so common?

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Stephen Pincock raised the question in an excellent short article in this weekend's Financial Times.

He asked Robert Loblay, an allergy specialist in the Royal Prince Alfred Hospital's allergy unit.

Said Loblay, "The short answer is that nobody knows."

The most popular hypothesis centers around an increase in peanut–containing foods being eaten during pregnancy and breastfeeding, with subsequent exposure and sensitization of babies to peanut protein allergens via the placenta or breast milk.

Here's Pincocks's piece.

    The Kernel of the Problem

    Word came from our son's school last week that we needed to avoid putting nuts, peanut butter sandwiches or muesli bars in our kids' lunchboxes.

    It turns out that one of the pupils has a pretty serious peanut allergy.

    The teachers, wisely, thought it best not to take any risks.

    There has never been a shortage of things for parents of young children to fret about, but these days peanut allergies must be close to the top.

    A highly sensitised person can react to as little as 1/2000th of a single peanut, and of all food allergies the peanut variety is most likely to be fatal.

    I was talking about this subject over dinner recently with a couple of my parents' generation.

    I could tell it was an issue they'd been primed for, because at the merest mention all four of their eyebrows raised and their voices notched up an octave.

    "Nobody had peanut allergies in our day," they exclaimed.

    "Where has it all come from?"

    I thought that was a pretty good question, so I put it to an allergy specialist in Sydney, Robert Loblay of the Royal Prince Alfred Hospital's allergy unit.

    "Perhaps 20 years ago, peanut allergy was relatively rare," he explained.

    "It suddenly appeared on the scene about 15 years ago and seems to still be increasing dramatically."

    In his unit for example, 15 years ago they would have seen a handful of children with a peanut allergy in a year. Now they are treating 15 to 20 every week.

    OK, but why?

    "The short answer," says Loblay, "is that nobody knows."

    The slightly longer answer is that there are a couple of hypotheses floating around, all based on the idea that something must have changed to expose infants to more peanut proteins over recent years.

    One idea that has emerged from a study in the UK is that moisturising creams and lotions containing low-grade peanut oil are being used more on children.

    In Loblay's view this isn't likely to be the main factor.

    Instead, he thinks that the increase in peanut allergy is probably a result of women eating more foods containing the nut during pregnancy and breast-feeding, thus exposing their babies to peanut protein via the placenta or breast milk.

    One piece of evidence in support of this is that food allergies tend to occur more often in countries where the food is more widely eaten.

    For example, Japan has a much higher incidence of rice allergy than in the west, while Scandinavian countries have a higher rate of fish allergy.

    "People tend to become allergic to things they are exposed to," explains Loblay.

    Allergy has a strong genetic element to it, but exposure to certain foods may direct the form that allergy takes, he explains.

    Another interesting point is that something like 80 per cent of children who come to Loblay's unit after experiencing a severe peanut allergy reaction - known as anaphylaxis - had the reaction the first time they ate food containing peanuts as babies.

    The reason this is interesting is that allergies need to be primed (like the couple I was having dinner with above).

    The first exposure doesn't normally trigger an allergic reaction, but it primes the allergy-related class of antibodies in our system, known as IgE antibodies, to wreak havoc next time.

    So the fact that kids are experiencing allergic reactions the "first" time they are exposed as babies suggests they had in fact already been exposed - either in the womb, or via breast milk.

    For the past three or four years, Loblay and his colleagues have been conducting a study of their own to test this idea.

    Each time a mother comes into their unit with a child who has a peanut allergy, they explain that it might have happened via breast milk and suggest to them that if they have another child, they might want to cut back on peanut ingestion while pregnant and breastfeeding.

    The Sydney researchers are collecting data to compare the families who cut back on peanuts for their subsequent child with families who didn't.

    "Even though we're still in the early stages, the data are looking very suggestive that the prevalence of allergy is significantly reduced in the next child," Loblay says.

    The findings will be important if confirmed, but we're still left pondering why peanut consumption would have increased so dramatically in recent decades.

    There are a few possible options, but one that's been suggested to Loblay by dietician colleagues is the shift toward more vegetarian diets.

    Women who have moved away from eating too much meat are often advised to increase their intake of seeds and nuts, he says.

    By doing so, they may have increased their children's exposure to a peanut allergy.

    That idea already has enough currency for pregnant women to be advised against eating too many peanuts.

    No matter how much you love peanut butter, it certainly seems that avoiding binges during pregnancy could be an appropriately cautious move.

********************

Every now and then you see a headline like the one up top: the story is always the same.

About 1.5 million Americans have peanut allergies.

Every year, 100 or more deaths in the U.S. occur after an inadvertent exposure to even the faintest trace of peanuts.

December 18, 2005 at 02:31 PM | Permalink


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Comments

I will venture a knee jerk, unresearched, and uneducated guess. The newer, more powerfull ultrasound machines and the zapping of the foetus, repeatedly over the gestation period, might be messing with thye delicate and everchanging biochemical ballet of foetal cellular differentiation.
Now, if I find out that my arrogant musing is substantiated, I will be somewhat vindicated, but pissed.

Posted by: Hugo | Dec 19, 2005 8:07:39 AM

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