Peanut allergies in the western world are increasing. There is no doubt about that. But there is plenty of doubt about why this is happening. Is it because children are more likely to be exposed to peanuts early in life than they used to be? Many foods and cosmetic products are formulated with peanut protein or peanut oil. Or is the opposite the case? Are peanut allergies increasing because parents have been so careful to keep infants away from peanuts that their immune system doesn鈥檛 learn how to deal with this allergen at an early stage? Arguments can be made for both possibilities. In Israel, peanut allergy is extremely rare, affecting only about 0.04% of children. Is it because there is no peanut exposure? Not at all. One of the favorite snack foods is Bamba, a type of peanut flavoured puff. Israeli children have plenty of peanut exposure and a low allergy rate while in Canada, the US and Britain where parents have been keeping children away from peanuts until they are three years old, the peanut allergy rate has doubled in the last ten years and now stands at about 1% of all young children. The thinking has been that higher doses of peanut early in life are more likely to trigger the formation of IgE antibodies that are critical to an allergic reaction. If peanuts are avoided till later, a more mature immune system may not be as sensitive to the allergenic protein. In other words, it has been assumed that there is a straight-forward dose repose effect. The greater the exposure early in life, the greater the chance of developing an allergy. However, this may not be the case. At zero exposure there is no chance of developing an allergy. That there is no doubt about. An allergic reaction requires previous exposure that resulted in the formation of antibodies. It is on subsequent exposure that an allergen-antibody reaction results in an allergy.
But once we climb above zero exposure, things become more mysterious. Small doses set the stage for a future allergic reaction, but some experiments are showing that larger doses actually have a protective effect. There is some suggestive evidence from a study done on umbilical cord blood in babies at high risk for egg allergy. Babies who had the highest or lowest levels of antibodies to egg proteins were least likely to experience allergic sensitivities by the time they were six months old when compared with babies with mid- range antibody levels. Actually such a dose relationship shouldn鈥檛 come as a total surprise because this is just how allergy shots work. A large dose of an allergen when injected stimulates the formation of a protective antibody known as IgG instead of the troublesome IgE. The protective antibody neutralizes the allergen before it can react with IgE. So maybe the answer to cutting down on peanut allergies is exposure to just the right amount of peanut early in life, as seems to be happening in Israel. Here our exposure may be less, and that may just be the problem. Or maybe the fact that here we use diaper creams that contain peanut oil is an issue. Absorption from the skin may be more allergenic. The only way to solve the peanut mystery is through controlled trials. And this is happening. A British study will examine the effects of either total peanut abstinence, or that of exposing infants to varying doses on the development of peanut allergy later in life. It sure would be interesting to find out what is going on. I know that when I was going through school, we never heard of peanut allergies and the idea of a peanut-free school would have been laughable.Peanut allergies in the western world are increasing. There is no doubt about that. But there is plenty of doubt about why this is happening. Is it because children are more likely to be exposed to peanuts early in life than they used to be?
