Reduced exposure might increase allergic sensitisation

EDITOR,—Pamela W Ewan makes the important statement that the incidence of peanut and nut allergy is rising and that sensitisation seems to occur early in life.1 Regrettably, she does not provide any evidence to back her recommendation that “young allergic children should avoid peanuts and nuts to prevent the development of this allergy” and her extraordinary suggestion that avoidance should be practised until the age of 7. Hugh A Sampson, in the accompanying editorial, makes similar recommendations and further suggests that mothers who are breast feeding should eliminate peanuts from their diet.2

Firstly, there is no evidence that avoiding foods during lactation or early childhood prevents allergic sensitisation to these foods. Indeed, in certain cultures that consume large quantities of peanuts, peanut allergy seems to be less of a problem than it is in Britain. Secondly, allergic sensitisation may occur in utero, but no advice is given on maternal diet during gestation. Thirdly, exposure to peanuts and other food allergens during lactation and childhood may be important in the development of immunological tolerance and may prevent allergic sensitisation to these foods. Finally, avoidance measures would serve only to reduce exposure to peanuts to low levels, and this could paradoxically increase allergic sensitisation to peanuts: low dose exposure to allergens (rather than high dose exposure) favours production of IgE,3 and as little as 1 μg of inhaled allergen a year may be sufficient to induce allergic sensitisation via the airways.4

Prospective data comparing consumption of peanuts by children who are allergic to them and by atopic controls are required before broad policy recommendations are made. History contains far too many examples of uninformed health policies that were based on insufficient data and achieved unintended effects.