Some kids may outgrow tree nut allergies

Published 4:00 am Thursday, November 17, 2005

Tree nut allergies, once thought to be a lifelong condition, are outgrown by about 9 percent of affected children, according to a new study published this month.

Researchers from Johns Hopkins Children’s Center recently retested 278 children ages 3 to 21 who had previously been confirmed to have allergic reactions to tree nuts, including almonds, cashews, hazelnuts, pecans, pistachios, Brazil nuts, pine nuts, walnuts and macadamia nuts.

Patients who had a low level of antibodies, a marker of nut allergy, were asked to consume cookies that contained tree nuts. Nearly 9 percent of the test subjects passed the oral challenge without any allergic reaction.

”Allergic reactions to tree nuts as well as peanuts, which are not nuts but legumes, can be quite severe and they are generally thought to be lifelong,” said Dr. Robert Wood, director of the Division of Allergy and Immunology at the center and lead author of the study. ”Our research shows that for some children, however, lifelong avoidance of these nuts, found in countless food products, may not be necessary.”

Food allergies occur when the body mistakes something eaten as harmful to the body. The body produces antibodies to protect against the substance.

The antibodies cause a release of chemicals, including histamine, into the bloodstream, producing the allergic reaction in the eyes, nose, skin, throat or lungs.

There is no effective way to prevent nut allergy reactions, so those affected are simply advised to avoid eating nuts and carry injectable epinephrine in case of accidental consumption.

An estimated 1 to 2 percent of Americans are allergic to tree nuts, peanuts or both. Among test subjects, 68 percent had peanut allergies in addition to their tree nut allergies.

Previous research by the Hopkins physicians found that 20 percent of those with peanut allergies outgrow them. The latest study found that those who had outgrown their peanut allergies were more likely to outgrow tree nut allergies as well.

The authors said the study likely underestimated the percentage of patients who will outgrow their allergies because many of the test subjects who had lower antibody levels declined to participate in the oral challenge. Presumably, some of those also may have outgrown their tree nut allergies. Had those who declined the oral challenge had the same pass rate as those who participated, the resolution rate would have been nearly 22 percent, similar to that for peanut allergies, the researchers said.

The study found that only those patients previously diagnosed with fairly low levels of antibodies outgrew their tree nut allergies. And none of the test subjects with allergies to more than two types of trees nuts outgrew their allergies.

”These findings give allergists a safe guideline in deciding whether to advise their patients to continue avoiding tree nuts, or whether it’s time to try an oral food challenge to see if they’ve outgrown the allergy,” Wood said.

He also cautioned that oral food challenges should be conducted only under the close supervision of an allergist.

”What’s crystal clear is that children with these allergies should be regularly re-evaluated,” he says. That way, they don’t have to worry needlessly about a potentially deadly allergy.

Peanut and tree nut allergies appear to be on the rise in the U.S. A study conducted by the Mount Sinai School of Medicine in New York found that the rate of nut allergies in children doubled from 0.4 percent in 1997 to 0.8 percent in 2002. The researchers suggested that could be due to the increased allergenicity of peanuts when roasted, the use of soy formulas and topical ointments containing nuts, and children eating nuts when their immune systems are immature.

Clinicians believe that children may become sensitized to nuts if they are given nuts or nut products too early in life. Doctors generally advise parents to refrain from giving children nuts or peanut butter until after they’re 2 years old. For families with a history of nut allergies, parents should wait till age 3.

There is some debate among physicians whether a woman can sensitize a child to nut allergies while breast-feeding. Nursing mothers are often advised to avoid nuts or peanut butter until their child has been weaned.