By now, you’ve probably heard about the recent study, which showed that early consumption of peanuts lowers the risk of peanut allergy by as much as 86%.
The study, led by Gideon Lack of King’s College, London, and published in the New England Journal of Medicine in February, is the first randomized clinical trial conducted on preventing peanut allergy in children. Widely hailed as a game changer, the study’s findings are already affecting the advice given to parents.
Just last week my friend’s pediatrician counseled her to “stir a little peanut butter” into her 6-month-old’s rice cereal. She barely managed to avoid gaping at him in astonishment. Just two years earlier, with her first child, he had told her to avoid introducing peanuts for the first year.
After decades of conflicting advice and vague admonitions, parents may wonder whether such a dramatic change is actually warranted. Is the evidence any better now than it was ten years ago? And if the guidelines were so mistaken before, why have confidence in them now?
And, perhaps the biggest outstanding question of all: what, if anything, does this study mean for when to introduce other highly allergenic foods, like fish, tree nuts, or eggs?
Why Are Food Allergies a Major Concern?
The number of children with peanut allergy has skyrocketed in last 30 years. From 1997 to 2008 alone, the prevalence of peanut allergy among U.S. children more than tripled, climbing from 0.4% to 1.4%.
This rise is part of a larger trend. The prevalence of tree nut allergies more than doubled in the same period, and a shocking 8% of children are now allergic to one or more foods.
Complicating matters for concerned parents, the advice on when to introduce peanuts and other highly allergenic foods like eggs, fish, and tree nuts has been all over the map. In 2000, the American Academy of Pediatrics (AAP) issued clinical guidelines advising that for infants with a family history of allergies:
“Mothers should eliminate peanuts and tree nuts (eg, almonds, walnuts, etc) and consider eliminating eggs, cow’s milk, fish, and perhaps other foods from their diets while nursing. Solid foods should not be introduced into the diet of high-risk infants until 6 months of age, with dairy products delayed until 1 year, eggs until 2 years, and peanuts, nuts, and fish until 3 years of age.”
These recommendations were made on the basis of two studies, one showing a higher risk of eczema among children given solids before 4 months of age, the other showing an increased risk of allergies among infants introduced to solids at 3 versus 6 months of age. Neither of these studies were randomized trials.
After these guidelines were issued, more and more studies piled up showing no benefit of delaying the introduction of allergenic foods. In 2008, the AAP rescinded their earlier recommendations, stating that
“There are insufficient data to document a protective effect of any dietary intervention beyond 4 to 6 months of age for the development of atopic disease.”
In their update, the AAP carefully refrained from advising early or late introduction of allergenic foods. The new guidelines remained deliberately agnostic on the topic. But despite these changes, many pediatricians, like my friend’s, continued to advise that parents avoid giving their babies peanuts for at least their first year of life.
But now this latest study suggests that the 2000 guidelines, and many well-intentioned pediatricians and parents who followed them, may–perversely enough–have contributed to the rising incidence of peanut allergy, and perhaps other food allergies as well.
How Was The Latest Peanut Allergy Study Conducted And What Did It Find?
Gideon Lack and colleagues conducted a 5-year randomized trial to investigate whether early consumption of peanuts can prevent the development of peanut allergy.
Lack recruited 834 babies who were 7 to 11 months old and at high risk for peanut allergy, either because they had severe eczema or because they were allergic to eggs. These 834 babies were then given a skin prick test to screen for peanut sensitization. Seventy-six babies who already showed evidence of severe peanut sensitization, with skin wheals larger than 4 mm, were excluded from the trial. An additional 118 babies were excluded because their eczema was not severe enough.
The remaining 640 babies were divided into two groups: 540 babies who had no evidence of sensitization, and 98 babies who had evidence of some sensitization, with wheals of 1-4 mm in size. Half of each of these groups were randomized either to consume peanuts or to avoid peanuts completely until age 5. The consumption group averaged about 7.7 grams of peanuts per week, or the equivalent of about half a tablespoon of peanut butter.
The results were striking. For the babies who showed no evidence of early peanut sensitization, 13.7% of the avoidance group developed a peanut allergy by age 5, versus only 1.9% of the consumption group.
The results were just as dramatic for the babies who showed evidence of early sensitization to peanuts: 35.3% of the avoidance group developed a peanut allergy, versus only 10.6% of the consumption group.
Across the board, the percentage of infants developing a peanut allergy was quite high, because these infants were at high risk for peanut allergy; normally about 15-20% of infants with severe eczema or egg allergy will go on to develop a peanut allergy.
These results, from a careful and well-conducted randomized trial, are compelling, but alone they are unlikely to change the guidelines. There is still too much that we do not know. We do not know whether consumption would benefit the infants who showed signs of more severe early sensitization to peanuts, with skin wheals greater than 4 mm in size. We do not know whether these findings would apply other highly allergenic foods like eggs, fish, and tree nuts. And we do not know whether these children will continue to be able to tolerate peanuts if they were cease to consume them regularly–this last question is now being investigated by Dr. Lack’s team.
What Do These Findings Mean For Whether or Not I Should Feed My Baby Peanuts?
In an interview with Scientific American, Dr. Lack provided his own interpretation for parents.
For low-risk infants, without eczema, other food allergies, or a family history of food allergies, Dr. Lack counsels
“eating peanut butter as soon as weaning is established. You don’t want peanuts [as opposed to peanut butter] to be the first food because if the kid is gagging or choking, it could represent allergic manifestation but it may also just indicate the child hasn’t developed the coordination to eat solid foods.”
For high-risk infants, with severe eczema, other food allergies, or with a family history of allergy, such as those with a sibling with food allergies, he counsels:
“see[ing] an appropriate health care provider, which could be an allergist or a pediatrician, and have skin prick testing done for peanut as soon as these high-risk symptoms develop. If the child tests negative, the child should be encouraged to eat peanut at home. If the skin test is a small positive, like it was for some of the kids in our study, then the children should have their first exposure or consumption of peanut under medical supervision; and if they tolerate it they should be encouraged to continue to have peanut regularly in their diet for at least the first three years of life.”
How Do These Findings Fit With Earlier Research?
Dr. Lack was spurred to conduct this clinical trial after he found a ten-fold difference in the incidence of peanut allergies among children of Jewish ancestry living in the UK versus those living in Israel. Although genetically quite similar, 1.85% children of Jewish ancestry living in the United Kingdom have a peanut allergy, compared to only 0.17% of those living in Israel.
Dr. Lack theorized that early introduction of peanuts might be the critical difference between these two groups. Children in the UK rarely consumed peanuts before 1 year of age, whereas Israeli children typically begin consuming peanuts around 7 months of age, and average about 8 peanut-containing meals a month. One of the most common snacks given to Israeli babies is a peanut-coated puff called Bamba. It looks a lot like Cheetos, but without the bright orange cheese.
That early consumption of peanuts can lead to tolerance has been shown in animal studies. And, although the recent trial was the first to test whether oral exposure can prevent peanut allergy in children, oral exposure has been shown effective for treating children with severe peanut allergies. In one small clinical trial, children with severe peanut allergy who were randomly assigned to receive small, incrementally increasing doses of peanuts while under careful medical observation showed improved ability to tolerate very small doses of peanuts. Unfortunately, because of the high risk of adverse reactions, oral exposure therapy is not generally recommended for children with severe allergies.
What Does This Study Imply About Other Common Food Allergies?
While the results of this study do not directly address when to introduce other highly allergenic foods, like eggs, fish, and tree nuts, they are consistent with a growing body of human and animal studies, all of which finds that early consumption of allergenic foods can help prevent allergies.
Introduction of wheat before 6 months, for example, is correlated with a reduced risk of developing a wheat allergy. The same has been found for egg and cow’s milk allergies. Introduction of cooked, but not baked egg (in which the egg protein is denatured), between the ages of 4 to 6 months is associated with a lower risk of developing an egg allergy. One small clinical trial found a reduction in the incidence of egg allergy among high-risk infants with regular early exposure to egg powder starting at 4 months of age; unfortunately their sample was too small to exclude the possibility that this reduction was merely due to chance.
With the data we have at hand, we cannot conclude that early exposure reduces the incidence of other food allergies; the studies on other allergenic foods have either been observational or too small to be reliable. It is entirely possible, for instance, that the true causal path runs in the opposite direction, that parents delay introducing eggs, peanuts, tree nuts and other allergenic foods to infants whom they believe are at high risk of developing allergies.
Moreover, there are important, and as yet poorly understood, nuances to these findings:
Timing – Introduction of solid foods before 4 months of age in some studies has been linked with an increased risk of food allergies and an increased risk eczema for term and preterm infants. But… delayed introduction of cow’s milk has also been linked with eczema. Confusing, I know. These types of contradictions occur all over the allergy literature, and not just for food allergies. In response, some researchers have proposed that there is a critical “window of opportunity”, sometime starting around 4 months, when exposure leads to tolerance instead of sensitization.
Dose – Based on animal studies, some researchers have theorized that small doses of peanuts can lead to sensitization, whereas large doses lead to tolerance. Similarly, skin exposure, such as when creams containing peanut oil are applied to the skin, has been linked with sensitization, whereas oral ingestion has been linked with tolerance.
Normal Gut Flora – The development of tolerance may depend on having normal gut flora. Here’s what Dr. Lack had to say about this phenomenon in animal research:
“It’s very interesting that in animal models oral tolerance to food such as egg will develop by feeding young mice egg very early on—usually a single dose is enough to help prevent allergies. But that only works in mice that have normal gut flora. If you take mice that are germfree, those that have a sterile gut with no commensal bacteria, the phenomenon of oral tolerance does not occur.”
Gut flora can be adversely affected by antibiotics. And this alone is an excellent reason to avoid giving your baby antibiotics unless absolutely necessary.
The Bottom Line
In sum, there is no evidence that delaying the introduction of allergenic foods beyond 4 months of age reduces the risk of food allergies, and suggestive evidence that delaying their introduction beyond 6 or 7 months actually heightens the risk.
(Doesn’t this contradict the advice to breastfeed exclusively for the first 6 months? Sure. But, as I describe here, the benefits of exclusive breastfeeding beyond 4 months have been vastly overstated.)
There is also no evidence that avoiding allergenic foods during pregnancy or while nursing reduces your baby’s risk of developing food allergies. The current advice on eating these foods while pregnant or nursing has been whittled down to, as The Ontario Society of Nutrition Professional in Public Health puts it: “Pregnant women should avoid foods they are allergic to.” Ladies, now that you’re pregnant, please lay off the anaphylaxis.
But what about whether it is better to introduce other allergenic foods early? Dr. Lack’s approach to introducing peanuts seems sound, and after consulting with your doctor, I cannot see a good reason not to follow his recommendations for other allergenic foods as well.
And since this study came out, I have to confess that I have been a lot more conscientious about regularly giving nuts to my thankfully non-allergic kids.
Beyond that, it’s hard to say anything definitive, because the allergy research literature is frankly something of a mess–a jumble of seemingly contradictory findings which could arise from true “windows of opportunity” and dose-dependent effects. Or which could simply be the result of small sample sizes, multiple tests, inadequate controls, and the neverending pressure to publish, even before a finding has been properly vetted.
As just one example–and there are many–consider this study on allergic asthma: Early exposure to cockroach dung, rat feces, and mice feces before 1 year of age was associated with a reduction in the risk of asthma, but cumulative exposure up to age 3 was associated with an increase in the risk. What does this mean? I have no idea. And I certainly do not intend to change my behavior on the basis of these findings, nor do I imagine anyone else is will. What would we do? Bring home some cockroaches, mice, and rats with our newborn on they way home from the hospital and then fumigate after the first birthday?
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