A less tolerant nation
FEATURE - 27TH AUGUST 2019
The prevalence of allergies is on the rise in the UK and other developed countries. What is fuelling this modern phenomenon, and what can be done to address it?
Words: Jessica Brown
In recent decades, the prevalence of allergies among both children and adults in the western world has been steadily climbing. Today, around 50% of children and 45% of adults in the UK have at least one allergy, the total cost of which runs to hundreds of millions of pounds in primary and secondary care and prescriptions. The obvious question is, why is this happening? At present, there are several potential answers, but no clear consensus. Probably the most widely cited reason is the bacteria exposure theory, otherwise known as the hygiene hypothesis. This theory suggests that children exposed to poor hygiene in early life, and therefore more frequent low-level infections, have a lower risk of developing allergies, as a result of these infections serving to strengthen the immune system.
Adnan Custovic, professor of paediatric allergy at Imperial College London, says that in addressing this question, it is important that we don’t group all allergies together, as the precise causes for their increasing prevalence are likely to be distinctly different: “It is unlikely that the reasons for the increase in asthma cases are the same as for food allergies or hay fever, although there will be common threads.” But he believes that the hygiene hypothesis is probably an important part of the overall picture. “This hypothesis makes sense because you can see the huge differences in the proportion of children and adults with allergic diseases in affluent countries compared to lower and middle-income countries,” he says. “When you go to the latter, you can observe an objective increase in asthma and allergy desensitisation, so it seems to be linked to what I’d broadly describe as affluence.”
The bacteria exposure theory is a complex one to untangle, as in almost all other respects good hygiene and infection control are beneficial to our health. “We don’t want to go back to where we were 100 years ago; we want to have all the benefits of hygiene and vaccinations, but at the same time create ways in which we can expose children in early life to benign microbes,” Prof Custovic says. “We want to get to a position where we have proper balance between being clean and finding beneficial exposures to good bacteria.”
A window of opportunity
Research suggests that bringing up children in households with pets can be advantageous against developing allergies, but this only works when the children are young. Getting a pet later can indeed be problematic. “If a child grows up with an animal, it might protect them from allergies and asthma, but if they get one later in life, it may actually predispose them to the development of allergy,” says Dr Chris Rutkowski, consultant allergist and clinical lead for adult allergy at Guy’s and St Thomas’ Hospital and a consultant at The London Allergy Clinic in the Harley Street Medical Area. “There is a window of opportunity when you can teach the immune system to accept things; if you wait too long to get a pet, you can miss this flexible period.”
Aside from the hygiene hypothesis, another explanation for the recent burgeoning of allergies is our increased exposure to allergens. For example, the rise in asthma cases might be attributed to air pollution and the extensive use of chemicals in our daily environment, such as fragrances, cleaning products and tobacco smoke.
The same argument goes for the rise in food allergies in the western world in recent decades: we’re simply becoming exposed to more potential allergens than we were in the past, leading to new allergies. “We used to talk about milk and shellfish allergies, now we’re talking about sesame and buckwheat,” says Rutkowski. “These allergens weren’t prominent in our diets in the past, but they are now—especially in London, where we eat food from all around the world. We’re simply exposed to more.” These newer food allergies have been in the media spotlight in recent years, particularly in the aftermath of the death last year of 15-year-old Natasha Ednan-Laperouse, who tragically passed away following an allergic reaction to the sesame in a Pret-a-Manger baguette.
The industrial revolution
The general rise in food allergies and intolerances can also be partly explained by changes to how food is made and consumed. Since the industrial revolution, food production has come to rely ever more heavily on chemicals, including pesticides, fertilisers, preservatives, colourings, flavourings and sweeteners, which have conditioned our bodies’ responses.
The rise in food allergies isn’t limited to newer foods: from 2001 to 2005, there was a 117% increase in the prevalence of peanut allergy, which is responsible for more deaths from anaphylaxis—constriction of the airways—than any other food allergy. This is partly attributed to parents being more likely to avoid giving children common allergens early in life, in an attempt to minimise risk. Common advice given as recently as 2000 surrounding peanut allergies led parents to avoid feeding peanuts to their children until they were three years old—as well as pregnant women avoiding them during their pregnancy—but this attitude is changing, as researchers now emphasise the importance of introducing babies to small doses of possible allergens at a young age. “If you introduce peanuts early on, this seems to prevent the development of an allergy, because it presents the immature and malleable immune system to peanut allergens,” says Dr Rutkowski. “If you wait too long, this can promote the development of the allergy. The theory is that you have to do it at some point, and delaying makes no sense.” There aren’t many other ways to prevent the onset of allergies, Dr Rutkowski says, as their development seems to be due to a combination of genetic predisposition and exposure to environmental factors.
However, treatments are moving on quickly, says Prof Custovic. “With food allergies, up until a few years ago the best you could tell someone was to stay away from the food they were allergic to, which is a rather lousy way to treat disease. Now we’ve moved into desensitisation, which has already been successfully used for hay fever.” The aim of desensitisation is to gradually expose the patient’s immune system to increased levels of allergens through injections or tablets. “The first desensitisation injection for hay fever was administered in 1906 at St Mary’s Hospital, and this has now evolved from injection treatment to sublingual tablets. We’re trying to use the same approach to food allergies, but it’s complex. Feeding people low doses and building up their tolerances still isn’t ready for prime time as there are issues related to safety and how to administer it into the healthcare system.”
Ongoing research into oral immunotherapy treatment for peanut allergies is showing some promise, though, according to Dr Rutkowski. This method targets T-cells, which act as the immune system’s intermediary between our bodies and the environment, reprogramming them to see the allergen as friendly rather than hostile. Researchers at St Thomas’ and Guy’s have been giving patients small amounts of peanuts and gradually building the dose up, under observation in hospital, to improve their tolerance.
One problem these scientists are yet to overcome is that food allergies tend to come back when treatment stops. “You can make someone who is severely allergic to peanuts tolerate them, but if you stop treatment, they often lose tolerance—and we don’t yet fully understand why. With venom and pollen immunotherapy, you do three years of desensitisation treatment, then you’re done. But this isn’t the case with food immunotherapy—at least not yet,” says Dr Rutkowski.
Treatments are also increasingly focused on getting to the cause of allergies by targeting different biological pathways, says Dr Rutkowski. For example, rather than just treating symptoms with steroids and antihistamines, new treatments aim to pinpoint specific receptors in the body. The focus now is personalised medicine and more targeted treatment. This includes using component resolved diagnostics, an approach that seeks to identify the specific molecules causing sensitisation or allergy.
Genetic testing, which will allow scientists to determine whether a patient’s genome predisposes them to an allergy, is also on the horizon. “The question is what we do with this information, as we haven’t yet learnt how to switch the gene off,” Dr Rutkowski says. But some patients, he adds, are probably less concerned with these advances. “Allergies to food, pollen and venom can be completely overpowering. Patients want to be well and might not care that much about the genetic mechanisms—they want effective treatments. Allergen immunotherapy can offer a more permanent solution and it is available on Harley Street as well as in some NHS centres.”
Research is currently underway to better understand how to stop asthma from developing. Professor William Cookson, professor of genomic medicine at Imperial College London, wants to see if the community of microbes that exist in our respiratory tracts, otherwise known as microbiomes, could be responsible for asthma, which affects 350 million people around the world. “If you live on a farm or in an environment with lots of bugs around, you’re protected against allergies and asthma. When you move to cities in western societies, all the bugs in our airways and bowels lose a lot of diversity and good bacteria. Asthmatics seem to have bugs in their airways that live there and probably don’t do damage a lot of time, but which sometimes break through the linings of the lungs and cause disease,” he says.
Prof Cookson’s research is homing in on which bacteria are good bacteria. He expects the research to be completed within the next three years, and to influence medical treatment in the next decade. “We have to catch the harmful bacteria, grow them in a microbial culture and work out what they’re doing. We’ve been doing this for two years now, and we’re starting to get a good understanding of what’s going on down there. We’re on a clear path towards sorting things out.”
Late onset asthma
But the often-heard suggestion that rising levels of air pollution in our cities are the cause of the growing prevalence of asthma is apparently misleading. “There are lots of epidemiology studies showing that air pollution doesn’t cause asthma, but it can certainly make the symptoms much worse. Late onset asthma is less understood, but is often diagnosed in people who have been smokers.”
Other ongoing research for preventing asthma includes looking at cocktails of drugs fed to mothers during pregnancy, Prof Custovic says. However, he concedes that this, and any other treatment, might not be applicable to all patients, and more research needs to be done to identify who benefits from any specific intervention. “The most important thing to remember is that the idea that there might be a magic bullet is certainly not the case, and different interventions will be applicable to different people.”