The week began with the extremely welcome news that the LEAP study, which had been on-going on at Guys’s and St Thomas’ Evelina Hospital for the last 5 years, has come up with exactly the results that we had all hoped that it would: that eating peanuts from an early age is likely to protect against peanut allergy.
And now researchers in Sweden tell us that using a dishwasher may actually increase the likelihood of suffering from allergy. What on earth will Friday bring?…
The LEAP research was inspired by a 2008 observational study, also led by Dr George du Toit, one of the lead authors in the LEAP research. This study compared 5,000 Jewish schoolchildren in Israel with 5,000 Jewish school children in the UK. And it found that the incidence of peanut allergy among the children brought up in Israel, who ate peanut in significant quantities from a very early age, worked out at 0.17% while the incidence among the British schoolchildren, whose parents had been advised to avoid peanut consumption by both mother and child, during pregnancy, breastfeeding and infancy, was 1.85%.
But, as Drs Gruchalla and Sampson point out in an editorial in this week’s New England Journal of Medicine, the 2008 study was only observational, so ‘data from controlled studies was needed to provide reliable clinical guidance’. And now we have that data. At 5 years of age, the prevalence of peanut allergy amongst the group of atopic children in the LEAP study who avoided peanuts was 13.7%; in the group who consumed peanuts from around 6 months onwards the prevalence was 1.9%. (For the full research report see the NEJM here.)
Of course the research raises almost as many questions as it answers. Should the guidelines on early ingestion of peanut be changed immediately? If so, how much should the children eat? Will tolerance persist if the children stop eating the peanuts? Could the LEAP study findings also apply to other allergens – eggs? milk? other nuts? None the less, some degree of clarity will be very welcome to those parents of at-risk, atopic infants for whom guidance on whether they should avoid or consume peanuts has, up till now, been at best foggy and at worst non existent.
And will it also focus attention on routes of sensitisation? How does one become allergic to a peanut, or to anything else? If the very process of eating something prevents one becoming allergic to it, which would appear to be the conclusion to be drawn from the LEAP study, can one be sensitised to an ‘allergen’ by another route?
How is it, for example, that a child can have a serious, maybe anaphylactic reaction to a peanut when it has never eaten one? Can sensitisation occur via the skin? So could an eczematous child be sensitised to peanut by the peanut oils on which a number of eczema creams and emollients are based? If so, could the proteins be absorbed through the skin or only into blood stream if the skin was broken? And if so, and if such absorption did sensitise the child to peanut (or any other allergen), why is the body’s reaction so different to the allergen when it is absorbed through the skin rather than through the stomach?….
Well, researchers in Sweden, quoting the hygiene hypothesis which suggests that ‘microbial exposure during early life induces immunologic tolerance via immune stimulation, and hence reduces the risk of allergy development’ have been comparing the allergic status of children whose family use a dishwasher with those who wash by hand. And they have found that allergic disease is less common in families who was by hand than those who use a dishwasher, suggesting that ‘a less-efficient dishwashing method may induce tolerance via increased microbial exposure’.
Mind you, they do also note that ‘the risk was further reduced in a dose-response pattern if the children were also served fermented food and if the family bought food directly from farms’ so one does have to wonder whether other aspects of the family’s lifestyle might not have been as important as the dishwasher. (See here for the full report.)
Of course, in some quarters the hygiene hypothesis has now been has now been superseded by the micro biome hypothesis anyway – that it is not our exposure to external bugs that influences the chances of us developing allergies but the health of our population of internal bugs. But then it could be argued that a super clean plate could actively hinder a good bug from making its way via our fish fingers to join its fellow good bugs in our guts…. Time to log out, I think…