As Peanut Allergies Rise, Trying to Determine a Cause
Peanut allergy has become a nemesis for
increasing numbers of children and parents in recent years, forcing them
to maintain nut-free households and prompting many schools to ban a
childhood staple, peanut butter, from the lunchroom.
When a child is allergic to peanuts, families
must closely monitor everything the child eats both in and outside the
home, because accidental consumption of peanuts could prove fatal. Many
airlines no longer offer peanuts for fear that an allergic passenger
might inhale peanut dust and suffer a life-threatening reaction at
30,000 feet.
The prevalence of peanut allergy among
children in the United States has risen more than threefold, to 1.4
percent in 2010 from 0.4 percent in 1997, according to a study
by food allergists at Mount Sinai Hospital in New York City. Many
people with an allergy to peanuts are also allergic to one or more tree
nuts, like walnuts, pecans or almonds.
To help protect such people from inadvertent exposure to nuts, labels on packaged foods often voluntarily state whether they were prepared in a facility that also processes nuts.
Some cities have nut-free bakeries that now
sell products safe for allergic children, who can bring their own
special, albeit expensive, cake or cupcake to a party.
While experts doubt the necessity of some
extreme measures taken to prevent indirect exposure to peanuts, the
danger to someone with a peanut allergy who eats them is unquestioned.
The potentially fatal reaction, called anaphylaxis,
can occur with a child’s first exposure to peanuts: itchiness, swelling
of the tongue and throat, constriction of the airway, a precipitous
drop in blood pressure, rapid heart rate, fainting, nausea and vomiting.
Unless the reaction is stopped by an injection of epinephrine (adrenaline), anaphylaxis
can kill. In one infamous instance in 1986, Katherine Brodsky, 18, a
freshman at Brown University with a known nut allergy, died after eating chili that a restaurant had thickened with peanut butter.
There is no cure for nut allergies,
although several preliminary studies suggest that it may be possible to
temper a reaction to peanuts with immunotherapy. Like shots given for
pollen allergies, the approach starts with exposure under the tongue to a
minuscule amount of the offending peanut protein, followed by exposure
to gradually increasing amounts under strict medical supervision.
The latest study, conducted in Cambridge,
England, and published in The Lancet last week, found that after six
months of oral immunotherapy, up to 91 percent of children aged 7 to 16 could safely ingest about five peanuts a day,
far more than they could before the treatment. About one-fifth of
treated children reacted to ingested peanuts, but most reactions were
mild, usually an itchy mouth. Only one child of the 99 studied had a
serious reaction.
When immunotherapy works, the research
suggests, the severity of the allergy is lessened, enabling an allergic
person to safely ingest small amounts of the offending protein. It is
not known how long protection lasts without continued immunotherapy,
however, and the researchers warned that no one should try it on his
own. Further study is needed before the treatment can be used
clinically, probably years from now.
Meanwhile, everyone with a peanut allergy is advised to carry an EpiPen for emergency treatment.
Ideally, allergists would like to prevent the
development of peanut allergy in the first place. Experts had thought
that one way would be to keep fetuses and breast-fed babies from
exposure to peanut protein by restricting consumption by pregnant and
nursing women.
Various studies had suggested that early exposure to peanut protein by infants with allergic tendencies could sensitize them and lead to a serious peanut allergy.
In 2000, pregnant and nursing women were advised to avoid eating
peanuts, especially if allergies ran in the family. And new mothers were
told not to give babies peanuts before age 3, when digestive systems
are more fully developed.
But this advice did nothing to curb the steady climb in peanut allergies, and it was abandoned in 2008.
Today, the thinking is exactly the opposite.
Instead of restricting exposure to peanut protein by unborn or nursing
babies, the tiny amounts that may enter the baby’s circulation when a
pregnant or nursing woman eats peanuts might actually induce tolerance,
not sensitization.
In a recent study of 8,205 children, 140 of
whom had allergies to nuts, researchers found that children whose
nonallergic mothers had the highest consumption of peanuts or tree nuts,
or both, during pregnancy had the lowest risk of developing a nut allergy. The risk was most reduced among the children of mothers who ate nuts five or more times a month.
The researchers, led by Dr. A. Lindsay
Frazier of Dana-Farber/Children’s Hospital Cancer Center in Boston,
wrote: “Our study supports the hypothesis that early allergen exposure
increases the likelihood of tolerance and thereby lowers the risk of
childhood food allergy.”
They added that their data “support the recent decisions to rescind
recommendations that all mothers avoid peanuts/total nuts during
pregnancy and breast-feeding.”
The study was supported by Food Allergy Research and Education, a nonprofit, and published in December in JAMA Pediatrics.
According to an accompanying editorial by Dr. Ruchi Gupta,
an associate professor of pediatrics at Northwestern University, “some
studies actually showed that avoiding peanuts during pregnancy increased
the risk of a child developing peanut sensitization.”
Further support comes from studies of other
common food allergens. In an Israeli study of 13,019 infants, those who
were exposed to cow’s milk protein as a breast-milk supplement in the
first two weeks of life were less likely to become sensitive to it than infants first given cow’s milk much later.
An Australian study of 2,589 babies found that those first introduced to egg at or near 1 year of age were more likely to develop an allergy to egg protein than those first given egg at 4 to 6 months of age.
In her editorial, Dr. Gupta emphasized that
further research was needed to understand how maternal diet affects the
development of food allergies and “why more and more children are
developing food allergy and how we can prevent it.”
But for now, she said, “pregnant women should
not eliminate nuts from their diet, as peanuts are a good source of
protein and also provide folic acid,” which can help prevent neural tube defects.