NIH. US: It might seem obvious that the best way to avoid a food allergy is to
steer clear of the offending item. But a recent study, published in the
New England Journal of Medicine, suggests that just the opposite may be
true: strict avoidance from a very early age may be the wrong strategy
when it comes to kids at high risk of developing an allergy to peanuts
[1].
The study found that feeding peanut-rich foods to some high-risk
infants actually helps their developing immune systems learn to tolerate
peanuts better, apparently helping them avoid this serious allergy
later in life. While it’s too soon to recommend stepping up peanut
consumption among all babies, the findings provide striking new insights
into how food allergies develop and how they might be avoided.
One thing is clear: a growing number of
parents and schools are contending with children with peanut allergies.
In the United States, peanut allergies have quadrupled over the past 13
years and now affect more than 2 percent of Americans. This trend is so
troubling that some airlines have stopped serving peanuts on flights,
and it’s not uncommon for teachers to ask students not to bring peanut
butter or other peanut products to school.
The latest study arose from an observation by Gideon Lack of Kings
College London and his colleagues, published in 2008 [2], that Jewish
children in London developed peanut allergies at 10 times the rate of
their counterparts in Israel. Probing the eating habits of infants in
both countries, they discovered that parents in Israel often introduce
their babies to a popular peanut-based snack called Bamba around the age
of 7 months. In England, parents avoid such foods until kids reached
their first birthday or later.
To test their initial observation, the NIH-funded team enrolled 640
infants who were between 4 and 11 months old. All had severe eczema (an
allergic skin rash) and/or egg allergy, putting them at higher risk of
developing a peanut allergy. The children were divided randomly into two
groups. In one, parents were asked to feed their kids Bamba and other
peanut-containing foods at least three times each week until age 5. In
the other, parents kept their children peanut-free for the entire study
period.
Five years later, the Lack team gave each child an oral peanut
challenge. They found 17 percent of children on the peanut-free diet had
developed a peanut allergy, compared to only about 3 percent of the
peanut eaters. Among those children who started the study already with a
slight peanut sensitivity (as measured by a skin test), 35 percent of
peanut avoiders developed a full-blown allergy, compared with just 10
percent of peanut eaters.
In sum, the study found that adding peanut-based foods to an infant’s
diet reduced the risk of peanut allergy between 70 and 80 percent.
What’s more, the strategy appears to be relatively safe; researchers
reported no deaths during the study and no significant differences in
serious adverse events between the peanut avoidance and peanut
consumption groups.
Like all studies, this one does have its limitations. The researchers
didn’t determine how much peanut protein must be eaten and how long it
needs to be consumed to develop lasting peanut tolerance. It also isn’t
clear whether the same strategy would work for other common food
allergies, such as eggs, milk, and other kinds of nuts.
A second study, which dovetails with this work, involves a search for
genes that increase the risk of peanut allergy. In the NIH-funded
study, Xiaobin Wang of The Johns Hopkins University in Baltimore and
colleagues examined the DNA of more than 2,700 individuals—including
parents and children with and without clearly defined food allergies.
They discovered a region on chromosome 6 harbors genetic risk factors
for peanut allergy [3].
Wang’s team found no genetic changes there linked to milk or egg
allergy. But for peanut allergy, they identified certain regions within
the human leukocyte antigen (HLA) that likely contribute a significant
genetic risk. The HLA is complex of genes that encode proteins that help
to regulate the immune system and can be a hotspot for genes involved
in allergies.
These findings represent some of the most exciting developments in a
long time in understanding the causes and the potential means of
prevention for peanut allergy.
References:
[1] Randomized Trial of Peanut Consumption in Infants at Risk for Peanut Allergy.
Du Toit G, Roberts G, Sayre PH, Bahnson HT, Radulovic S, Santos AF,
Brough HA, Phippard D, Basting M, Feeney M, Turcanu V, Sever ML, Gomez
Lorenzo M, Plaut M, Lack G; the LEAP Study Team. N Engl J Med. 2015 Feb 23.
[2] Early Consumption of peanuts in infancy is associated with low prevalence of peanut allergy. Du Toit G, Katz Y, et al. J. Allergy Clin. Immunol 2008:122:984-991.
[3] Genome-wide association study identifies peanut allergy-specific loci and evidence of epigenetic mediation in U.S. children. Hong X, Hao K, Ladd-Acosta C et al. Nature Communications 2015 Feb 24;6:6304.
Links:
Food Allergy (National Institute of Allergy and Infectious Diseases/NIH)
The Immune Tolerance Network (ITN)
Learning Early about Peanut Allergy (LEAP) Study
Xiaobin Wang, Johns Hopkins University Bloomberg School of Public Health, Baltimore
NIH support: National Institute of Allergy and Infectious Diseases