Children exposed to air pollution at a young age are more likely to develop food allergies

Children exposed to air pollution at a young age are more likely to develop food allergies

The modern world is highly industrialized and urbanized. A side effect of this lifestyle change is the increase in food allergies. New research examines links between food allergies and prenatal or postnatal exposure to airborne pollutants, paving the way for future studies on possible gut sensitization through skin or respiratory tract exposure to pollutants through the dietary route.

Learn: Early life exposure to air pollution associated with food allergy in children: Implications for the “one allergy” concept. Photo credit: Africa Studio / Shutterstock

introduction

Food allergies are defined as “a specific immune response to certain foods” and are estimated to affect one in ten people worldwide. This proportion is probably even higher for children. In some cases, exposure can cause a life-threatening anaphylactic reaction to the food in question, often occurring within seconds or minutes. Food allergies are responsible for many emergency medical visits, high medical expenses, and limiting the ability to attend social gatherings with food. This can also lead to social isolation, bullying and bad moods. Food allergies therefore represent a health risk, an emotional challenge and a financial burden for the patient and caregiver as well as for society due to the associated health impairments and loss of productivity.

Food allergies are different from other allergies that make up the “Atopic March,” namely asthma, allergic rhinitis and eczema, which represent progression of the disease in childhood. One notable departure is the 30-year lag in the increase in the prevalence of food allergies compared to the first wave of allergies that included the other three conditions, leading to it being dubbed the “second wave” of allergy.

Second, food allergies are due to intestinal exposure to allergens, while the others are due to skin and respiratory tract exposure. However, scientists are currently reconsidering this hypothesis in light of evidence that skin contact can also lead to sensitization to food allergens, called the “gut-skin dual exposure hypothesis.”

Air pollution plays a significant role in the development of other allergies, but less is known about its role in food allergies. The current paper is published in the journal Environmental research aims to identify any links between exposure to air pollution and the recent rapid increase in the prevalence of food allergies in China. This would support their triple exposure hypothesis of food sensitization including intestinal, skin, and respiratory exposure.

"If this hypothesis is correct, air pollution is thought to have led to the first and second waves of allergy epidemics, suggesting the concept of a 'one-allergy' disease."

The study was conducted on a cohort of children who participated in the China Child Family Health (CCHH) project between September 2011 and January 2012. The researchers asked children about food allergies, living environment and lifestyle. Over 2,500 children from 36 kindergartens (3-6 years old) took part and their parents answered the questionnaires.

The prevalence of food allergies over the child's lifetime was queried using the International Study of Asthma and Allergies in Childhood (ISAAC) form, based on the occurrence of eczema, hives, swelling of the lips or eyes, or diarrhea after consumption of a particular food.

Outdoor air pollution was measured in the form of three pollutants, namely sulfur dioxide (SO2), nitrogen dioxide (NO2) and particulate matter with a diameter of ≤10 μm (PM10), which are markers of industrial pollution, traffic pollution and mixed pollution respectively. The average pollutant concentration per day was used to estimate the daily exposure for each child depending on the child's distance from the monitoring station.

Additionally, indoor air pollution was represented by the presence of new furniture, renovation, mold or moisture, and condensation on windows. The latter two represent ventilation adequacy, and the first two are significant sources of air pollutants.

Prenatal exposure was defined as during pregnancy, by trimester, and postnatally from the first postnatal month to the last month before questionnaire administration.

The researchers excluded demographic variables that could confound the results and other factors such as whether the household had dogs, smokers and common cleaning habits.

What did the study show?

It was reported that around one in seven children had a food allergy, with an increased risk in men, those whose parents had atopic diseases and if the house was rarely cleaned. The risk was highest in the 3-4 year old age group compared to 5-6 year olds.

The risk of food allergies was increased in children with prenatal exposure, e.g. B. if her parents decided to renovate the house and buy new furniture during the pregnancy or if the house was poorly ventilated. For example, if mold/dampness was reported during pregnancy, the offspring were doubly at risk for food allergies. On the other hand, if the baby inhaled fumes from new furniture or lived in a poorly ventilated house, food allergies increased by 50% and 40%, respectively.

Outdoor air pollution has also been linked to childhood food allergies. For example, NO2, reflecting air pollution from heavy traffic, increased the risk of food allergy by 25% and 38% between exposure quartiles, depending on whether exposure occurred before or after birth. Similarly, PM10 and SO2 have been associated with an increase in the risk of food allergy in childhood after postnatal exposure by approximately 40% and 30%, respectively.

Previous studies have shown an increase in egg or milk allergies in children exposed to volatile organic compounds (VOCs) compared to unexposed children. Similarly, propylene glycol and glycol ethers (PGEs) are commonly emitted from new furniture. Exposure to these substances in the bedroom increased the risk of the child showing signs of hypersensitivity by 80%.

Overall, air pollution appears to be associated with FA in childhood between three and four years of age. This confirms the results of previous studies showing, for example, an increase in peanut allergy at one year of age with higher NO2 levels.

What are the effects?

The study provides some evidence that food allergies can arise from respiratory exposure, supporting the single allergy mindset.

“Our studies suggest that both the first wave of the allergy epidemic (including eczema, asthma and allergic rhinitis) and the second wave of the allergy epidemic are sensitive to the same environmental pollutants, particularly air pollutants.”

This could help control this second wave of food allergies sweeping the developed world, as the ability to control a form of allergy such as asthma by, for example, purifying the air we inhale could also be valuable in preventing food allergies.

“Our study suggests that the rapid increase in food allergies among children in China is related to developments in recent decades.”

A perhaps distorted pattern of economic development led to massive rural-urban migration, coupled with huge increases in air pollution from a wave of industrial development.

Scientists have reported that babies as young as two in Chongqing had food allergies in nearly 8% of cases, up from just 3.5% in 1999. This increasing trend can also be seen in other developed countries such as Canada, the US and the UK.

“Food allergies are expected to continue to increase in the near future, particularly in low- and middle-income countries” (LMIC), as these nations measure their prosperity based on economic growth and urbanization. The results of this study could reveal new methods of intervention to prevent or treat such allergies, as they all have the same cause.”

Further research should use a prospective design with more air pollutants to correctly estimate the prevalence of food allergy and rule out an association with the reverse cause-effect direction.

Reference:

• Zhang, X. et al. (2022). Exposition gegenüber Luftverschmutzung im frühen Leben im Zusammenhang mit Lebensmittelallergien bei Kindern: Implikationen für das „Eine-Allergie“-Konzept. Umweltforschung. https://doi.org/10.1016/j.envres.2022.114713. https://www.sciencedirect.com/science/article/abs/pii/S0013935122020400

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