Wetenschap - 14 februari 2019

Allergies explained - Harry Wichers clears up misunderstandings in his book

tekst:
Tessa Louwerens

Cats, peanuts or pollen: who isn’t allergic to something these days? Why is that? And is everything we call an allergy really an allergy? WUR researcher Harry Wichers has written a book about this. ‘Allergy has become a kind of catch-all term for all unpleasant reactions.’

Text and photo Tessa Louwerens

It is a lovely spring day and people on the terrace are enjoying the first watery spring sunshine. Not Lisa, though. The birch trees are flowering and she is allergic to their pollen. She can’t order a slice of apple pie either, because it might come from a factory where nuts are processed as well. And Lisa has a severe nut allergy.

Harry Wichers draws this picture in the opening scene of his book The Achilles Heel of Allergy, which was published last December. Wichers is a biochemist and allergies and immunology are among the topics he works on at the Fresh Food & Chains department of Wageningen Food & Biobased Research (WFBR). ‘I notice that people are not always very understanding about allergy. You hear people say it’s all between their ears. Whereas it can be very difficult to live with.’

Catch-all term

When Atlas publishers asked him over six years ago to make his knowledge about allergies available to a wide readership, Wichers was enthusiastic from the start. Every rainy weekend he worked on his book at home. Unfortunately the publisher pulled the plug on the project halfway through – which was a severe blow – but Wichers still finished the book and found a new publisher in Wageningen Academic Publishers.

Lisa’s story, which Wichers begins his book with, is not a made-up one but is based on a postdoc he works with. Only her name has been changed. The example illustrates how hard it can be to live with allergies. And it seems as though more and more people have them. ‘If you ask 100 people at the market in Wageningen whether they are allergic to any foods, about 20 of them will say they are,’ says Wichers. ‘If they all go to the doctor, it wil turn out that two of them have an actual food allergy. Allergy has become a kind of catch-all term for all unpleasant reactions.’

So there is quite a bit of confusion about what an allergy is, exactly. Well-meaning legislation has played a part in that too, according to Wichers. The European Union, for example, has designated 14 substances that must be listed under ‘allergy information’. Wichers: ‘They include the milk sugar lactose, whereas there is no such thing as a lactose allergy.’ An allergy involves an excessive – and in fact unnecessary – reaction by the immune system to harmless substances (usually proteins) from outside the body. People who are lactose-intolerant, about 70 per cent of the world population, lack an enzyme that is necessary for breaking down lactose in the gut. Without the enzyme, bacteria set to work on the milk sugar and that leads to abdominal cramps, gas and sometimes diarrhoea. 

Strawberries

People who have a strong reaction to strawberries are not, strictly speaking, allergic either, says Wichers. Strawberries contain histamine, a substance that is also released in the body during an allergic reaction by the immune system to a particular substance. The symptoms that the strawberry histamine can cause in oversensitive people are the same as those of an allergic reaction, but they come about without any involvement of the immune system.

Wichers says these examples demonstrate that the differences between an allergy, an intolerance and a sensitivity are not just a case of nit-picking about names. ‘It is important to establish how often allergies really occur, to be able to do something about them as much as anything. Because if someone really is allergic, that has major consequences. If you don’t know the cause, you can’t start the right treatment.’

Iron curtain

About 5 per cent of children and 2 per cent of adults in the western world currently have a true food allergy, Wichers writes in his book. In other parts of the world, such as Africa, the percentage is lower. This can partly be explained by differences in diagnosis and registration, but it is also because people in the west tend to live in cleaner environments. The idea behind this cleanliness hypothesis is that a bit of contact with dirt hardens the immune system so that it doesn’t react to every little thing.

It is not just foods that can cause allergic reactions. One third of Dutch adults suffer from respiratory tract allergies such as hay fever or a house dust mite allergy. Hygiene may play a role here too, but in this case it is the other way round, explains Wichers. ‘That’s because you are not allergic to the insect itself but to its poo. If you have slept on the same pillow for five years, it consists of about 20 per cent dead house dust mites and their excreta. So it’s not a bad idea to wash your pillow a bit more often, or buy a new one.’

Achilles heel

For now the best advice for people like Lisa is to avoid substances to which they are allergic. Wichers: 'It was believed for a long time that this was the only option. But now there is some light at the end of the tunnel.’ Large-scale studies have revealed that children who eat fried peanut snacks at a young age are less at risk later of developing a severe peanut allergy. Another study showed that children who are allergic to cow’s milk protein grow out of the allergy faster if they eat cake or muffins with milk in them. Researchers at WFBR are working with the Erasmus Medical Centre in Rotterdam to find out precisely which substances are formed when allergenic foodstuffs are baked, which could explain this phenomenon.

This means that allergies, just like the apparently invulnerable Achilles of Greek mythology, have their weak spot, says Wichers, referring to the title of his book. ‘But finding it is not as simple as shooting one arrow.’

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Harry Wichers will be giving a talk about his book De achilleshiel van allergie in the town library at Stationsstraat 2 in Wageningen, at 15:00 on Saturday 23 February. Admission is free.


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