Previously I blogged on how the incidence of both skin and food allergies among kids has been growing in America. In particular, the prevalence of childhood peanut allergies has grown five-fold over the past decade from 0.4% in 1997 to 2% in 2010. This is an astounding increase.
One (speculative) explanation (Vox.com) is the hygiene hypothesis, which posits that society has become too clean and hygienic. Essentially, children aren't exposed to enough bacteria, viruses, and possible allergens early on, which in turn inhibits the development of their immune system. In other words, an immune system that hasn't been properly trained (by exposure) to distinguish "good" (self or harmless) antigens from "bad" (pathogenic) antigens may make mistakes in the future by attacking "good" antigens (e.g. peanuts) like an ill-trained attack animal.
The counter-intuitive remedy is to expose the child to the harmless allergen early in life so that the immune system "gets accustomed to it". In this study (randomly-controlled trial), 530 infants were either fed with a diet that contained peanuts or fed with a diet without peanuts. Then the two groups were compared a few years later for peanut allergies (NYTimes):
"In the study, conducted in London, infants 4 to 11 months old who were deemed at high risk of developing a peanut allergy were randomly assigned either to be regularly fed food that contained peanuts or to be denied such food. These feeding patterns continued until the children were 5 years old."
The results were striking:
"Parents of half of them were told to avoid peanuts. The other half were told to feed their children at least six grams of peanut protein per week, the equivalent of about 24 peanuts, spread over three or more meals. The preferred food was Bamba, an Israeli snack made of puffed corn and peanut butter. The children were given another allergy test when they turned 5. Only 1.9 percent of those who were fed peanuts were allergic to them, compared with 13.7 percent of the children in the group that avoided peanuts. An additional 98 infants had a weakly positive test when the study began, suggesting they were on their way to developing a full-fledged allergy. Among those children, only 10.6 percent of those fed food containing peanuts developed that allergy by age 5, far less than the 35.3 percent rate for children whose parents avoided feeding them peanuts."
Among children who scored negative on the initial allergy test (to ensure that they could eat peanuts safely), the peanut-fed group had a seven-fold lower rate of peanut allergies than the group who avoided peanuts by age 5. This is a huge effect. Note that the general population rate of 2% peanut allergies is much closer to the 1.9% of the peanut-fed group than the 13.7% of the control group which suggests that many kids in America are getting peanuts in their diet.
As a sidelight, the preferred food for peanut intake (presumably because kids like them) in the study was something called Bamba (Figure 1). They appear to resemble peanut flavored sugar corn puffs:
"Bamba is one of the leading snack foods produced and sold in Israel. It has been marketed since 1964 with no decline in sales. Bamba makes up 25% of the Israeli snack market... Bamba is made from peanut butter-flavored puffed maize... Some describe it as "Cheez Doodles without the cheese."
Based on this study The New England Journal Editorial Board made the following recommendations:
"In the meantime, we suggest that any infant between 4 months and 8 months of age believed to be at risk for peanut allergy should undergo skin-prick testing for peanut. If the test results are negative, the child should be started on a diet that includes 2 g of peanut protein three times a week for at least 3 years, and if the results are positive but show mild sensitivity (i.e., the wheal measures 4 mm or less), the child should undergo a food challenge in which peanut is administered and the child's response observed by a physician who has experience performing a food challenge. Children who are nonreactive should then be started on the peanut-containing diet."
Please consult your doctor if you have any questions. My guess is that many kids these days are getting sufficient peanuts in their diet to avoid the higher peanut allergy rate associated with a total lack of peanuts in the diet. It is hard to say whether there is an optimal peanut intake rate for young children, and what that rate is. Rather the key conclusion from this study is that it can be harmful to completely avoid peanuts (unless you are already allergic to them).
The authors mention that one issue with their study is that there was no placebo used (in the no-peanut control group). Perhaps this can be remedied in future studies with the goal of repeating this astounding result. In addition, it would be useful to try this approach (i.e. early exposure) to other food and skin allergens.
Figure 1. This Israeli peanut-based snacked reduced the incidence of peanut allergies in young children. What is Bamba?
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