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To Anyone of Generation X or older often feels that food allergies are much more common today than in his youth. If they remember that they are rare or nonexistent at school, their own children will have allergic classmates or may have one themselves.
According to the Food Standards Agency, estimates suggest that about 5 to 8% of children and 1 to 2% of adults are affected by food allergies in the UK. Recent headlines on deadly allergic reactions, such as that of two Pret a a Manger customers, reinforce the impression that food allergies are more common.
So, is the impression correct and what is the cause? And what has gone wrong in our body that we could be killed by something as harmless as a sesame seed?
Since 1906, when the word "allergy" was used for the first time, the number of people affected has increased. Asthma has probably always been a problem, but, according to ancient evidence, it was exceptionally rare.
Hay fever has been documented for the first time in the 19th century. The doctor John Bostock was one of the first to collect data. When he traveled the country looking for people with hay fever, his total number of cases was ridiculously small for a modern audience: 28.
Morell Mackenzie, a British doctor of the 1880s, noted that since "summer sneeze goes hand in hand with culture, it may be inferred that the higher the intellectual tendency, the more developed the trend" . As soon as they appeared, allergies were linked to those more distant from rural education.
Between the 1950s and 1980s, as the 2007 studies on temporal trends of allergic disorders in the United Kingdom and 50 years of asthma explain, the number of people suffering from hay fever, Eczema and asthma "has increased dramatically". Conversely, the air (according to Defra) has become less polluted, no more. Even with less allergens, our symptoms seem to spread more widely.
Before the 1990s, peanut allergy was so rare that almost no data on it was collected. In a 2015 article in the Journal of Allergy and Clinical ImmunologyPaul J. Turner noted that while hospitalizations for anaphylaxis increased by 615% between 1992 and 2012, the incidence of fatal anaphylaxis has not increased. Turner and colleagues felt that "growing awareness of the diagnosis, changing behaviors in patients and health care providers" could be contributing factors. Although peanut allergy is much more prevalent, the number of its deaths has not increased.
Professor Katie Allen of the Murdoch Children's Research Institute in Melbourne, Australia, who has been studying HealthNuts for 10 years, who is closely following a food allergy in 5,300 Australian children, was stunned by her initial findings. At the start of the trial, they expected to find about one in 20 of their one – year – old subjects tested positive for nut allergy, but found the double. Allen explains, "The outbreak of food allergies has occurred after the asthma epidemic / hay fever. We call it the second outbreak of allergic disease. "
Genetic studies are on track to unravel the relationship between our DNA and allergies. Large case studies of, for example, 50,000 people with eczema, or 60,000 people with hay fever, are starting to show that there could be only 20 to 40 of our 20,000 genes that make up the genetic architecture of allergy.
Dr. Manuel Ferreira, an asthma genetics specialist at QIMR's Berghofer Medical Research Institute in Brisbane, Australia, explains that in a new study (about to be published), he discovered with his team that "genetic risk factors related to food allergies significantly overlap with those of other allergic diseases, such as asthma and hay fever".
Genes play a role, but the fact that we've been carrying similar DNA for thousands of years without being so allergic suggests that the environment is a key factor. Dr. Paul Gray, a specialist in pediatric immunology and allergy at Sydney Children's Hospital, explains, "The net genetics of the population change little over time, so outbreaks are influenced by non-genetic changes."
While the symptoms of different conditions vary by type and severity, what binds these irritants is that they all constitute an overreaction of the body's immune system when exposed to a normally harmless trigger. Gray explains that "allergy is" an immune recognition crash leading to the establishment of an aggressive response against something alien but harmless, with adverse consequences for the ## 147 ## # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # 39; host. "
Nobody knows the exact reason for why there are more food allergies today, but experts now think there are three factors.
The first is the delayed introduction of allergens. For years, all over the world, allergists had advised infants to avoid the consumption of potentially allergenic food products. Not only was this incorrect, but it may have also played a leading role in the food allergy epidemic we are witnessing today.
Professor Gideon Lack of King's College London, lead investigator of the LEAP study (Learning Early Learning on All Peanut Allergy) revealed that "among children who avoided peanuts, 17% had developed a peanut allergy to the age of five. Remarkably, only 3% of children randomized to eat peanut snacks developed an allergy at the age of five. The children involved in the trial were already suffering from severe eczema and / or an allergy to eggs (both powerful predictors of nut allergy).
The introduction of potential allergens at the same time as transferring a child into a solid seems like a good idea. It's a brave thing though, as a parent, to risk an exposure. Dr. Gray explains, "Most parents are starting to realize that early introduction of food is essential, but many do not feel brave enough to do it at home and hospital resources do not exist not to introduce it to the hospital. This must be corrected. "
The second contributing factor of food allergy (and more generally of allergy) concerns the human microbiome and the micro-organisms that are our "long-time friends". After birth, the body learns about its environment by coming into contact with a range of substances, from bacteria in which we are choked when we travel in the genital canal to the breast milk we are fed. Subsequently, the proximity of animals and natural environments increases the risk of exposure to a wide variety of bacteria, in the air, on the soil and in our diet. All these elements contribute to populating our body, but especially our gut, microbiota. It is such an important part of the human being that the microbiota is more numerous than us in our own body: humans are made up of something between 27 and 37 cells; but we carry about 100 tons of these organisms in us. We are amazingly complex ecosystems. The assumption of "old friends" or hygiene postulates that modern life has compromised our microbiome: our immune system can now incorrectly classify harmless substances as a threat.
The complexity of our microbiomes has led some to be wary of the conclusions drawn from the "old friends" hypothesis. A recent systematic review (Hygiene Hypothesis in the Development of Asthma: Is Hygiene to blame?) Called for "caution", considering too general assumptions to explain the complex nature of an illness such as as asthma and the ways it presents in different parts of the disease. world.
Nevertheless, imbalances in intestinal ecology have been strongly related to allergies.
As adults, the ecology in our gut is well developed, but we can always help to influence it. Professor Graham Rook, immunologist at the Center for Clinical Microbiology at University College London, explains that "the crucial point is the contact with green spaces and the natural environment, as well as the avoidance of antibiotics and factors limiting transmission. from the maternal microbiota to the infant. And we need a varied diet with many fruits and vegetables because these products preserve the biodiversity of the microbiota. "
Probiotics stimulate the growth of the microbiota. The fact that people with severe allergies have a distinctly less diverse (and less dense) intestinal flora suggests that the future of allergy treatment could be probiotic interventions. But you can not just go to the supermarket and take a probiotic drink in the trade and expect it to be effective. A mass produced probiotic has about the same success as false teeth. Scientists are working on custom probiotic therapies, but their treatment has been safe and effective for many years.
Amazing research such as Hunt for Origin of Allergy and Innate Immunity and Asthma Risk have compared genetically homogenous groups with very different lifestyles, respectively the Finnish and Russian urban populations of Karelia, as well as the Amish children. traditional and more industrialized Hutterites. farms in the United States – and how they exhibit huge disparities in the prevalence of allergy. This science shows that it is the distance and the absence of exposure to the natural environments that fuel the epidemic of allergies in modern life.
The last, third factor of food allergy, also related to urban life, is associated with the curious fact that there is an approximate geographical extension of food allergy. Scientists have begun to notice that the prevalence of food allergy tends to align with the geographical availability of sunlight. Professor Carlos Camargo in the United States, Professor Katie Allen and her Australian colleagues have explained in many papers and studies how a lack of exposure to sunlight – and a resulting vitamin D deficiency – can make infants three times more likely to have egg allergy and a staggering 11 times more likely to have peanut allergy.
Urban living makes it harder to get regular exposure to natural environments. We also spend more time indoors, making vitamin D deficiency more prevalent in the population, but especially in children. In the UK, parents are advised to "cover the exposed parts of your child's skin with sunscreen even on cloudy or overcast days".
As we gather more and more, it is the green spaces and natural environments between us that are rare, carrying with them countless opportunities for our immune system to discover the world around us and that we have essential access to sunlight. And while many factors come into play, urbanization levels appear to be one of the most powerful predictors of the prevalence of allergy in a population, both in the past and in the past. the future.
• Change of primate: how the world us Made We redone by Vybarr Cregan-Reid is published by Octopus (£ 16.99). To order a copy for £ 14.61, go to guardianbookshop.com or call 0330 333 684. Free UK rates from £ 10, online orders only. Minimum Phone Orders £ 1.99
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