Youngsters are developing peanut allergies earlier because of exposures in babyhood

By Janet Raloff

Web edition: December 11, 2007

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NOT NUTS. Despite their name, peanuts are legumes akin to soy and peas. However, like true nuts—those that grow on trees—peanuts can cause serious food allergies. Indeed, these tasty legumes are the most common source of food allergy in the United States.

Credit: iStockphoto

Peanuts are a protein-rich snack food packing plenty of vitamins and trace nutrients. However, these legumes can elicit potentially life-threatening immune reactions within the one in 100 American adults who are allergic to them. Rates of peanut allergy are even higher among children. And the really disturbing news: A new study finds that the age at which this common food allergy first shows up is falling.

Today, peanut allergy typically emerges in early toddlerhood, a team of Duke University researchers reports in the December Pediatrics. "That's almost a year earlier than what we knew, scientifically, a decade ago, "explains A. Wesley Burks, a pediatric allergist who coauthored the new study.

Although children outgrow many allergies, peanut allergy is not typically one of them. Among people who develop immune reactions to this food, 80 percent retain their allergy for life.

The new study began, Burks says, after Duke immunologists noticed that they were encountering younger patients with peanut allergy. To investigate, the researchers pulled entry records and medical charts for all 140 young patients who had come in with the allergy since 1988. Poring over the records confirmed a fall in age at first diagnosis throughout this period—one that proved more dramatic than expected, Burks told Science News Online.

Nationally, the rate of food allergy appears to be increasing, according to a 2006 report of a National Institutes of Health expert panel. The most striking increase, it noted, has been for peanut allergy, which is also the most common food sensitivity. Because some allergies can be avoided by delaying a child's initial introduction to certain foods, in 2000 the American Academy of Pediatrics recommended that parents "consider" keeping peanuts, tree nuts, fish and shellfish out of the diet of kids under age 3.

Burks acknowledges that most parents aren't aware of this recommendation. On the other hand, most peanut allergy shows up in children that had already exhibited allergic reactions to other foods—typically eggs or milk. Many affected children also had skin sensitivities as infants, such as eczema or atopic dermatitis, and a parent or sibling with allergies, although not necessarily to food.

Against that background, you would think parents of the most vulnerable kids would be especially careful about introducing peanuts into the diet. And they might well have been. Indeed, Burks suspects that most initial introductions to peanuts in his young patients were inadvertent. Either a child encountered items that contained unlabeled traces of peanuts—perhaps a jelly bean, certain flavorings used in medicines, or any of several baby lotions (see Unexpected Sources of Peanut Allergy). Or perhaps the kids encountered peanut allergen in the air when others were eating, handling, or cooking foods that contained the legume.

But for now, Burks' team has no firm leads on why peanut allergies are showing up earlier. The Duke group and others will be probing that in the next few years.

Homing in on the problem

Children with peanut allergy in the new study showed the expected history of vulnerability. For instance, four in five had parents or a sib with some form of allergy. Four in five children also had personally experienced atopic dermatitis, two in every three suffered from asthma, and more than half had allergies that triggered runny noses. Moreover, blood tests from two-thirds of the youngsters turned up antibodies highlighting sensitivity to other foods, typically eggs or tree-nuts.

Half of the young patients were born between 1988 and 1999, the rest between 2000 and 2005. The average age of their peanut allergy's onset was significantly different between the two groups—roughly 29 months old for the pre-2000 birth group, versus 15 months for children born since 2000. Within the first group, half of the children developed peanut allergy by 21 months of age; for children born since 2000, half developed their allergy by the time they were 14 months old.

In hopes of teasing out factors that contributed to the trend of earlier allergies, Burks' group is participating in a Food Allergy Research Consortium that has been given $17 million to study food allergies—especially to peanuts. One facet of the 5-year program, which is sponsored by NIAID, is investigating the use of shots to desensitize people with peanut allergy. In addition, some 400 infants with milk and egg allergies will be studied for signs of immunological differences that distinguish those who outgrow their allergies from those who retain them lifelong.

Currently, some 30,000 people a year are hospitalized for food allergy in the United States, and 200 die during an allergic episode. One concern, Burks notes, is that children who develop peanut allergy earlier than in the past might face a lower-than-usual chance of outgrowing their life-threatening affliction—one that requires constant vigilance.

Such an allergy can even crimp one's social life. Consider the poor teenage girl whose lips swelled up after being kissed by her boyfriend (see A Rash of Kisses). Hours earlier, the boy had eaten peanuts, to which the girl was allergic.

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