Asthma and food allergies: Discovered why they change over time

Allergies can develop as children, but they can also develop into adulthood, at age 50 or 60. Until now, the mechanism that influences the variability of allergies over time was unclear. Sometimes allergies resolve spontaneously in early childhood, while others appear suddenly throughout life.

The most innovative and recent evidence shows that the origin of allergies is only partially determined by genetics, but the triggering factor is the intestinal microbiota, which forms from conception onwards and matures in the first two years of life. This influences the immune system's programming, either protectively if a symbiotic relationship is established with the individual, or negatively if the microbiota is not in tune with the host, resulting in increased susceptibility to allergic diseases at any stage of life.

Not just genetics

"Until a few years ago, we were convinced that our fate as allergic sufferers depended exclusively on genetics. But it's not just our genetic makeup that determines whether we're born predisposed or not to develop allergies such as asthma, food allergies, and atopic dermatitis, which affect us not only in childhood but can appear for the first time in adulthood, or even in old age. The key factor that comes into play is the intestinal microbiota, an ecosystem of billions of microorganisms that dictates our clinical fate by deciding if and when the expression of genes that predispose us to diseases such as allergies changes," explains Vincenzo Patella , President of the Italian Society of Allergology, Asthma and Clinical Immunology (SIAAIC) and Director of the Internal Medicine Unit at the Salerno Health Authority.

Our genetic 'score'

“The microbiota is like a pianist playing our genetic score: if it is in balance with its host, the melody is harmonious and the body functions well, but if it is disturbed by external factors not foreseen by our evolution, such as the increasingly widespread use of cesarean sections, excessive exposure to antibiotics, an inappropriate diet, pollution, or stress, the melody becomes strident, increasing the risk of developing allergies,” says Alessio Fasano , an internationally renowned scientist among the first to decipher the role of the microbiota, which is revolutionizing the understanding of allergic diseases, pediatrician and gastroenterologist at Massachusetts General Hospital in Boston, professor of Pediatrics at Harvard Medical School and Professor of Nutrition at the Harvard T.H. Chan School of Public Health.

The first 1000 days of life

From this perspective, the first 1,000 days of life dictate our susceptibility to potential changes in the microbiome that can trigger allergies throughout our lives. The more in tune the microbiota with the host during this period, the lower the future risk of developing asthma and food allergies and beginning the "allergic march" that transforms from a genetic predisposition to a full-blown disease.

This was revealed by two recent studies published in Annals of Allergy, Asthma & Immunology and Gut Microbes, which analyzed the scientific literature, taking into account research and evidence on the role of the microbiota during pregnancy and infancy and how the early stages of life are crucial for "educating" immune cells to distinguish between harmless substances and potential dangers.

Immune tolerance

In particular, the study on Gut Microbes, coordinated by Fasano, shows how certain bacterial species play a crucial role in the development of immune tolerance in the first 1,000 days of life. "Specifically, the reduced presence of Bifidobacterium and certain Clostridia strains has been associated with a higher risk of food allergies and atopic diseases. These microorganisms produce short-chain fatty acids, which are essential for strengthening the intestinal barrier and promoting the maturation of regulatory T cells (Treg), which prevent inappropriate immune reactions to foods. In contrast, children with allergies often have a microbiome characterized by poor diversity and a higher abundance of Enterobacteriaceae, a condition that promotes inflammation and loss of tolerance," explains Fasano.

And it is precisely the microbiota that is the key theme of Fasano's lecture, which opens today's National Congress of the Italian Society of Allergology, Asthma and Clinical Immunology (SIAAIC), in collaboration with the World Allergy Organization (WAO), taking place in Milan. The world's leading experts will discuss respiratory, food, skin, drug, and hymenoptera venom allergies, with a focus on severe forms such as anaphylaxis and severe asthma. Pollution and climate change, increasingly emerging risk factors for allergic and immunological diseases, will also be at the center of the debate, along with strategies to combat the globally spreading allergy "epidemic." This trend not only represents a growing clinical challenge but also has a significant economic and social impact, requiring targeted prevention and intervention tools, starting in the early stages of life.

Allergies and the elderly

"In recent decades, allergies have become a true global epidemic. The incidence of diseases such as rhinitis, asthma, atopic dermatitis, and food allergies is constantly increasing, in all age groups, especially in industrialized countries," Patella observes. "Today, it is estimated that over a third of the world's population suffers from some form of allergy, with a marked increase especially among children. In our country, asthma affects 10% of under-18s, food allergies affect 6-8% of children, and 10% suffer from skin allergies," he states. "As for adults, 5% of the population suffers from asthma, 3% from food allergies, 10% from skin allergies, and 15-20% from allergic rhinitis. Added to these are all patients who suffer from allergic reactions to medications, which account for approximately 10% of all adverse drug reactions reported in Italy, while reactions to the venom of hymenoptera, bees, and mosquitoes are among the most common. "The prevalence of allergic diseases, such as wasps and hornets, is around 3%. Approximately 30% of the population may suffer from multiple allergic diseases. This condition significantly increases the severity of symptoms, making them more persistent and difficult to manage. Consequently, therapies become more complex, often requiring combined and prolonged treatments, with a significant impact on quality of life and the sustainability of the healthcare system," Patella emphasizes.

Elderly people more exposed

Older people are at greater risk of developing allergies, which can not only worsen but also appear for the first time later in life. "As we age, the immune system undergoes changes such as immunosenescence, which can accentuate an unbalanced response to allergens. Therefore, if we start out at a disadvantage, with dysbiosis of the microbiota in early life, aging will only increase the risk of developing allergic reactions even in old age," observes the SIAAIC president. "The bacterial flora in older people tends to become less diverse, with a reduction in beneficial species, such as Bifidobacterium, and an increase in pro-inflammatory bacteria. The result is a decreased ability of the microbiota to promote immunological tolerance and a greater predisposition to allergies." The constant increase in allergic diseases therefore represents a global public health challenge today. A thorough understanding of the mechanisms by which the microbiota influences the immune response is therefore a priority.

"The goal is to identify innovative strategies, based on diet, probiotics, prebiotics, or targeted interventions in the first months of life or even before birth, that can promote microbial balance and strengthen immunological tolerance," Patella concludes. "This will help stem the allergy epidemic and improve the quality of life of millions of people, paving the way for new prevention and treatment options."