Epidemiological trends in food allergy

The global prevalence of food allergies has continued to rise in the past 30 years. Currently, about 5% to 10% of the world's population suffers from food allergies, with the prevalence among children reaching 8% to 10%, which is significantly higher than that of adults.； At the same time, the allergen spectrum and onset characteristics show obvious regional differentiation and new characteristics with the iteration of dietary structure. It has been listed by the WHO as one of the key public health issues to be prevented and controlled in the 21st century.

Last year, when I participated in an allergy screening project at a community child care center in Hangzhou, I met three children diagnosed with wheat-dependent exercise-induced allergy in one morning. When I first entered the clinic 15 years ago, I could not encounter two cases in a month.

There is actually a lot of debate in the academic community about the nature of this upward trend. There is a school of thought that this is not really an "increase in the incidence rate" at all, but an increase in public awareness and the popularization of testing methods. In the past, many conditions were regarded as "weak gastrointestinal" and "naturally prone to eczema", but now they are clearly classified as food allergies. ； There is even over-diagnosis - many institutions only rely on positive serum IgE tests to label people as allergic. In fact, many people are just "allergic" and do not show clinical symptoms at all after eating the corresponding foods. This part of the falsely high data also drives up the overall prevalence rate.

However, scholars who conduct long-term cohort studies obviously do not agree with this statement. For example, a study released by the Peking Union Medical College Allergy Department team in 2020 used a unified oral food challenge test (the gold standard for food allergy diagnosis) to compare national multi-center samples in 1999 and 2019. In the past 20 years, the prevalence of food allergy in children aged 0 to 3 in my country has increased from 2.7% to 7.9%. With the exact same diagnostic standards, it cannot be said to be caused by overdiagnosis, right?

Interestingly, the allergen spectrum differs greatly in different regions, and even the common allergens in the same country change in different generations. For example, peanuts are the top allergen in European and American countries all year round, accounting for almost 25% of the causes of severe allergic reactions in children. In the past, the proportion of peanut allergies in our country was less than 1%. In recent years, with the popularity of nut snacks, it has increased to 3.8%, and is still rising. In the early years of our science popularization, we always said that the most common allergens are eggs, milk, and seafood. In the past two years, we have found that the allergy rate to fresh fruits such as peaches and mangoes has increased very quickly. Many people are even allergic to quinoa and chia seeds, which have been popular recently. No one had heard of such cases 10 years ago.

As for why the prevalence rate has increased so rapidly, the most mainstream one is the "hygiene hypothesis". To put it bluntly, everyone's living environment is too clean now. Children are exposed to less symbiotic bacteria and environmental microorganisms from an early age. When the immune system is developing, they have not seen real "bad guys". They easily regard harmless proteins in food as invading pathogens. When they encounter them, they initiate an immune attack and naturally become allergic. This statement is supported by real data. Domestic surveys show that the prevalence of food allergies among children growing up in rural areas is 32% lower than that of children of the same age in cities. The prevalence of food allergies among farm children in European and American countries is only 1/3 of ordinary urban children. However, some scholars do not recognize this, saying that rural areas in developed countries are quite clean now, so why is the disease rate still rising? They prefer pots that use food processing methods. For example, many prepackaged foods are baked at high temperatures and sterilized by high pressure. After processing, the spatial structure of the proteins in milk and eggs has changed. On the contrary, they are more easily recognized as foreign bodies by the immune system and are more allergenic than fresh ingredients. Some people have also suggested that it is a problem of insufficient vitamin D. Nowadays, children do less outdoor activities and do not get enough sun. Insufficient vitamin D levels will affect the establishment of immune tolerance. This is also supported by cohort studies, but there is currently no solid evidence of cause and effect. Everyone has his own theory.

In fact, no matter how noisy the academic community is, at the clinical and public health levels, the most practical thing is to first understand the trends and do a good job of grounded science popularization. I once met a parent who, after reading some popular science on the Internet, was afraid that his baby would be allergic, so he stopped giving eggs and milk from the beginning of complementary feeding. As a result, when he was 3 years old, his baby was 6 centimeters shorter than his age. When he was found to be severely malnourished, he was more likely to get sick. Don’t take it too seriously. Last year, a high school student was admitted to the emergency department. He ate a bite of mango mousse for his birthday. He had never been allergic to mangoes before, but this time he had a swollen throat and was admitted to the ICU. This kind of delayed, new-onset allergy in adults is becoming more and more common, so everyone should be careful.

In general, the rising trend of food allergies will definitely continue in the short term. With the integration of global diets, more allergens that have not been seen before may emerge. Whether you are a researcher or ordinary people, it is always right to be more careful. There is no need to be overly anxious. If you really suspect that you are allergic, go to a regular hospital for a provocation test. Don’t just rely on a test report and dare not eat anything. It will be more gain than loss.