domingo, 29 de marzo de 2015

Peanut Allergies: Prevention by Early Exposure? | NIH Director's Blog

Peanut Allergies: Prevention by Early Exposure? | NIH Director's Blog

Peanut Allergies: Prevention by Early Exposure?

Peanuts and peanut products
Credit: United States Department of Agriculture
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.
[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 Communications2015 Feb 24;6:6304.
Food Allergy (National Institute of Allergy and Infectious Diseases/NIH)
Xiaobin Wang, Johns Hopkins University Bloomberg School of Public Health, Baltimore
NIH support: National Institute of Allergy and Infectious Diseases

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