2023-11-14 21:27:26
Why do modern children have allergies so often and is this related to the increasing level of sterility in which we live? These and other questions are answered in the book “Allergy. Cruel games of immunity,” answers medical anthropologist Teresa MacPhail. With the permission of the Alpina publishing house, we publish the chapter “Microbiome and food allergies.”
If you want to better understand how modern lifestyles (including food production methods, diet, antibiotic use, and obstetric practices) are causing some of the most serious allergy-related problems, you may well find yourself in the company of the miniature a blonde woman named Katherine Nagler, sensitive and deeply educated. To her students she is Dr. Nagler, but to her friends and colleagues she is simply Katie. No matter who I talked to, all the specialists unanimously said her name as soon as food allergies were discussed. I immediately realized that Nagler was one of the best immunologists in the world. Her research focuses primarily on the role of the gut microbiome in the development of food allergies in children. She has been doing this work for several decades and she herself remembers very well the moment when in the late 1980s. Allergy rates began to rise for the first time.
“I saw it with my own eyes,” Nagler says, displaying several graphs on the computer screen facing me. It’s a clear spring day and we’re sitting in her office at the University of Chicago. “I have children, now they are 23 and 27, so I followed this situation, so to speak, in real time. For example, when they were in school, they were forbidden to bring cupcakes with them. Around the late 1980s or early 1990s, as food allergy rates began to rise, the American Academy of Pediatrics recommended that pregnant and nursing women and children under 4 years of age at risk of developing allergies avoid peanuts and allergenic foods. This was completely wrong advice and only added fuel to the fire because it accelerated the growth of allergic reactions. Now, on the contrary, everyone insists on the speedy introduction of such products into the diet.”
Nagler indirectly refers to the famous study “Learning Early About Peanut” (LEAP), conducted in the United Kingdom and the United States under the leadership of Dr. Gideon Luck of King’s College London and published in the medical journal The New England Journal of Medicine in 2015 The results showed that years of misguided recommendations to parents not to give peanut foods to children under 3 years of age resulted in an increase in the frequency and severity of peanut allergies. Infants enrolled in the study, aged 4 to 11 months, were randomly divided into 2 groups. In one group, their parents continued to follow the recommendation to avoid peanuts, while parents in the other group were advised to introduce peanuts into their babies’ diets as soon as possible.
All children underwent skin prick testing for peanut sensitivity. Among those who tested negative, the incidence of peanut allergy at age 5 years was 13.7% in the avoidance group and just 1.9% in the consumption group. Among children who tested positive for peanut sensitivity, the prevalence of allergy was 35.3% and 10.6%, respectively. A recent study in Melbourne, Australia, found that changes in dietary guidelines for peanuts in 2016 following the success of LEAP resulted in a 16% reduction in peanut allergies in infants.
It is clear that eating peanuts in infants has a protective effect
However, Nagler understands why parents are often hesitant to introduce allergens into an infant’s diet. After all, should they trust the same “experts” who gave them the wrong advice just a few years ago! In addition, according to the scientist, there is still no convincing evidence that early exposure to an allergen is always good.
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“A person may have sensitivity before introducing solid foods,” Nagler explains. — Children experience allergic reactions during the first year of life. This means they may have been sensitized through breast milk or skin. If you introduce such a child to allergens early enough, he will have a corresponding reaction. So introducing allergens into your diet early is risky—but we now know that avoiding them isn’t good either.”
And what does all this give us? Nagler’s biggest concern is the sensitization of the immune system. How does the human body learn to tolerate certain foods and begin to react negatively to others? She is convinced that food allergies as a phenomenon are an element of generational change.
“People will claim that this never happened in their family,” she explains. — Allergies can occur at any time in a person’s life. Previously, she appeared between the ages of 2 and 5 years. Now we are increasingly faced with the occurrence of food allergies in adults. Previously, it was believed that reactions to milk, eggs and wheat might be “outgrown.” But now we see that such a disease can accompany a person throughout his life.”
In other words, the situation has changed. Very much. And not for the better.
Food allergies are a sign of a more serious problem
Nagler shows me slides with various changes, and I can barely keep up with her. She speaks quickly, partly because she has so much to tell me. Katherine lists various theories regarding the causes of allergies, including the hygiene hypothesis, and then stops at a slide that shows aspects that likely affect the immune system: diet, caesarean section, changes in food production, breastfeeding.
“The idea is that factors from modern industrialized lifestyles have caused changes in commensal bacteria,” Nagler says. “Commensal bacteria” is, let me remind you, a term for all the so-called friendly bacteria that live inside or alongside our body. “Inflammatory bowel disease, allergies, obesity, autism—all these are non-communicable chronic diseases. And they were all related to the microbiome,” explains Katherine.
And here it is – Nagler’s answer to the most important question regarding why the number of allergies is growing. Changes in the composition of the microbiome—all the bacteria and viruses that live in the gut and help break down food into fuel for cells—lead to changes in immune function.
Recent research has revealed a link between diet, antibiotic use and gut bacteria in the development of allergies. A 2019 study found that healthy babies’ guts contain a special class of bacteria that protect once morest allergies, but babies with cow’s milk allergies do not have these bacteria.
A little later, the results of another study were published: scientists from Boston’s Brigham Hospital found that five or six specific strains of intestinal bacteria in infants appeared to protect them from developing food allergies. The project’s lead scientist, Dr Lynne Bry, suggested that our lifestyle has the ability, for better or worse, to “reboot the immune system”.
Фото: triocean / Shutterstock / Ftodom
Another study found that eating a lot of cheese may inadvertently worsen allergy symptoms because bacteria found in some cheeses produce histamine, a natural compound that helps trigger an effective immune response. Scientists at the University of California, San Francisco have discovered a link between three types of gut bacteria and the production of a fat molecule called 12,13-diHOME (oxylipin). In our gastrointestinal tract, oxylipin reduces the number of Treg cells, which, as we have already found out, play a decisive role in curbing inflammation. The study found that children with high levels of these three bacteria were at increased risk of developing allergies and asthma.
Nagler explains: “The gut is kind of the headquarters of the microbiome. It contains a lot of immune cells, especially in the colon. There are the most of them – both in terms of diversity and, of course, in terms of quantity. There are trillions of them out there.”
In short, most people living in the 21st century have themselves changed the composition of their microbiome
According to Katherine, the real culprit is our diet. When we eat processed foods rich in sugar and fat instead of high-fiber foods, the beneficial bacteria in our gut have nothing to feed on. We don’t give them the food they really need.
“We co-evolved with our microbes,” Nagler says. “But now we don’t have enough food for them.” And without this food they simply will not survive.”
In addition, we use antibiotics that kill not only the bacteria that cause sore throats and sinusitis, but also our gut bacteria. We also eat meat from animals that have been given low doses of antibiotics to help them gain weight. Nagler believes that all of this has a big impact on our own microbiome. According to her, we experiment on ourselves, but the effect of such experiments is extremely harmful.
Katherine developed a new theory called the barrier regulation hypothesis. Essentially, the gut and skin microbiome regulate what is allowed into the body and what is not. Commensal bacteria living on the skin and in the intestines play an important role in maintaining barrier function. Nagler explains that a layer of epithelial cells is all that stands between us and what surrounds us: these cells make sure that everything that enters our body is either inhaled or ingested.
Indeed, researchers recently discovered a link between a gene encoding an antiviral protein in the gut, changes in the gut microbiota, increased intestinal permeability and severe allergic skin reactions in mice. The gut microbiome is a complex, balanced mixture of different types of bacteria, viruses and fungi. Mice that lacked the gene for the antiviral protein had a transformed microbiome (in other words, the number and types of different bacteria and viruses in them changed significantly). This suggests that the immune system has developed ways to fight microbes in the gut to maintain balance. When the composition of the microbiota undergoes changes, the various responses of the immune components also change, resulting in a negative impact on ourselves. This shows that genetics and environment (changes in the gut microbiota) interact to cause allergies, but also supports Nagler’s broader point that altered gut microbiota can have a direct effect on allergies.
Let’s look once more at Avery August’s definition: immune cells are the “caretakers” of the body.
The barrier regulation hypothesis fits perfectly with the concept that our immune system as a whole, including the microbiome, controls what is and what is not part of the body. Without the regulation provided by these barrier cells, proteins can pass through the skin or intestines into the bloodstream, where they encounter immune cells. The immune system of an allergy sufferer is fully functional—it simply does the job it was designed to do. The whole problem is that she is being asked to do something completely different from what she was originally trained to do. At least that’s what Nagler thinks. From this point of view, allergic disease is a problem of the barrier and not necessarily of the immune system.
Katherine explains that all creatures, even invertebrates, have corresponding microbiota that perform vital physiological functions. Without microbiota there would be no life at all. The human gut encounters antigens from hundreds of trillions of commensal microbes and more than 30 kg of dietary proteins per year. The cells that make up the intestinal barrier must distinguish which of the “guests” are dangerous (that is, they are pathogens – harmful external bacteria or viruses) and which are harmless. Nagler and her former student Dr. Onyinye Iweala, an immunologist at the University of North Carolina School of Medicine, recently published a review linking the human microbiome to food allergies: “It is becoming increasingly clear that the functional epithelial barrier is involved in a close interaction with innate immune cells and resident microbiota, is critical for the establishment and maintenance of oral tolerance.” Simply put, this means that a healthy immune response to food depends on a complex balance between epithelial cells, the friendly bacteria that live inside us, and the types of foods we eat. Changes in any part of this balance can lead to great trouble, as we saw with Elizabeth’s children at the beginning of this chapter.
From Nagler’s perspective, Elizabeth’s theory—that antibiotics caused her children’s food allergies—may not be so far-fetched. Changes in the gut microbiome in infants and young children may increase the risk of developing allergic reactions as they get older. And, it seems, the most important thing is the characteristics of the environment at the earliest stage of child development.
Scientists have found that by the age of 3 the microbiome becomes incredibly stable.
Before this age, any changes in it appear to be critical to the development of allergies (or lack thereof). Findings from a mouse study conducted by the Pasteur Institute in Paris demonstrate the role of gut microbiota in the development of a healthy immune system between 3 and 6 months of age—the developmental stage when most infants are first introduced to solid foods. After its introduction into the diet, the number of bacteria in the intestines, as research shows, increases 10-100 times. It is this stage of rapid growth and development of the microbiome, called “pathogenic imprinting,” that appears to determine a person’s susceptibility to inflammatory diseases such as allergies and autoimmune disorders in adulthood. Theoretically, antibiotics can critically affect this stage of development, thereby increasing the risk of any allergic diseases.
And so far, scientific evidence confirms this*. A study from Rutgers University and the Mayo Clinic found that children under 2 years of age who are prescribed antibiotics are at increased risk of developing asthma, respiratory allergies, eczema, celiac disease, obesity and ADHD. The study included 14,572 children born in Olmsted County, Minnesota, between 2003 and 2011. If antibiotics were prescribed in the first 6 months of life, the risk increased dramatically. The scientists found that 70% of the children they observed received at least one antibiotic during the first 48 months of life (usually to treat respiratory or ear infections). Another recent study found that antibiotics may promote the growth of non-pathogenic fungi in the human gut, which may increase the severity of respiratory allergies. Finally, a study among infants in Finland and New York found that cesarean section and antibiotic use correlated with changes in the gut microbiome and increased risk of allergies in children.
Photo: Natalia Deriabina / Shutterstock / Ftodom
These findings don’t surprise Nagler. During our conversation, she repeatedly emphasized that vaginal birth provides the baby with so-called primary colonizers – special bacteria. As the baby moves through the vaginal canal, it is exposed to its mother’s friendly bacteria. Breastfeeding then introduces even more beneficial bacteria into the baby’s intestines.
“An organism is colonized by bacteria in a specific ecological sequence,” explains Nagler. “The first in line are bacteria that produce lactate. These are followed by those that are spread through breastfeeding. If you skip these two steps, as many people do, the microbiome will be disrupted.” The first 100 to 1,000 days of life “are critical for the development of the immune system,” she said.
Research has shown that babies born by cesarean section were not exposed to “good,” harmless primary vaginal bacteria, but were exposed to potentially dangerous hospital-acquired strains. One recent study found that probiotics containing lactobacilli, the same bacteria found in breast milk, reduced SCORAD scores in children under 3 years of age with moderate to severe atopic dermatitis or eczema (although no measurable benefit was seen in milder forms of the disease).
Breastfeeding during the first 3 months of life has also been linked to a reduced risk of respiratory allergies and asthma.
In a study of 1,177 mother-infant pairs, breastfed infants had a 23% lower risk of developing allergies and a 34% lower risk of developing asthma by age 6 (but only if there was no family history of asthma). was). However, if breastfeeding was alternated with formula, it did not reduce the risk of developing these diseases. If a mother added formula to her milk, the protective effect virtually disappeared. (An important note for readers who are mothers with infants: If you’re feeling a little panicked right now, please calm down. There are many good reasons for having a C-section and choosing formula rather than breast milk. We’ll come back to this in a moment, but it’s worth It should be noted that it is quite complex, and many relationships have not yet been identified.)
Nagler reminds me that cattle ranchers for years gave low doses of antibiotics to cows for commercial reasons—to make them gain weight. In addition, we consume foods that are low in fiber and highly processed, with added sugar and fat. This means that the food that enters our intestines is significantly different from what our ancestors have been eating for thousands of years. And all of this, of course, affects the types of bacteria that live inside us.
Even something as simple as changing your bedding can change a person’s microbiome (we’ll take a closer look at how chemicals play a role in these changes later in the book). The Danish Childhood Asthma Center and the Department of Biology at the University of Copenhagen conducted a joint study: they examined dust samples from the beds of 577 infants and compared them with respiratory samples taken from 542 of these children at regarding 6 months of age. Scientists found 930 different types of bacteria and fungi, and also established a correlation between the bacteria contained in bed dust and the bacteria found on children sleeping in these beds: the two populations of bacteria were not completely identical, but most likely directly influenced each other . Increases or decreases in the number of respiratory bacteria reflected changes in their numbers on the infants’ sheets. Research shows that changing bedding less frequently may be beneficial for the health of your sinus and respiratory tract microbiome.
Essentially, a greater diversity of bacteria around and within us has an overall positive effect on the functioning of the immune system. Many of the experts I spoke with are calling for a return to a simpler, less technological lifestyle. Much of this relates to what foods we consume and how we produce them. One of the leading allergists wants to conduct a control study to prove that our modern lifestyle and habits negatively affect the immune system.
“Let us imagine,” he said, “that a group of people were forced to return to a way of life that humanity led much earlier. They eat food grown without pesticides. Their diet contains whole grain components, and in a wide variety. They do not use dishwashers or detergents. Do you know what will happen then? There will be no allergies. I would really like to prove it.”
Cover photo: Antonina Trushina / Shutterstock / Fotodom
* The idea that antibiotic use is to blame is criticized, in part, because it may be nothing more than a correlation and the real culprit may be infections, not the antibiotics themselves (especially since not all children receiving antibiotics develop allergies) .
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