Study: Urban green areas reduce risk of allergies in children
Researchers at the University of Tartu and the Estonian University of Life Sciences have found that children who grow up near green spaces with a diverse community of soil bacteria are significantly less likely to develop allergies later in life.
Nature and medical researchers at the University of Tartu began studying the city's green spaces during the COVID-19 pandemic. Unable to travel abroad to collect samples for a more ambitious project, they instead gathered 743 samples from green areas across the university town. According to Meelis Pärtel, professor of botany at the University of Tartu, the effort made Tartu one of the best-mapped cities in the world for soil microbes.
"The study's most exciting finding was that we identified one specific group of environmental bacteria whose diversity was linked to children's allergy risk: the greater the diversity, the lower the risk of developing allergies," Pärtel said.
The group in question is gammaproteobacteria, a broad class of microbes found in environments ranging from the ocean floor to the human gut.
"Why the diversity of this particular group showed the strongest association is not yet fully understood because every study raises new questions. One possible explanation is that this group includes a number of pathogens, so the immune system has to learn which microbes are harmful and which are not," Pärtel added.
For example, some bacteria in this group cause salmonella infections and bloody diarrhea, while others produce vitamin K in the gut and compete with disease-causing microbes for space.
In addition to analyzing biodiversity in green spaces, the researchers examined health data from 148 children born in Tartu. Comparing those records with the soil samples, they found that children whose nearest green space with a rich community of soil bacteria was more than about 1 kilometer from their home were significantly more likely to develop allergies.
How does exposure to bacteria strengthen the immune system? Humans have coexisted with naturally occurring environmental microbes throughout their evolutionary history. Continuous exposure to these microbes helped train the immune system to distinguish truly dangerous organisms from harmless ones. In today's carefully managed urban environments, however, that contact is much more limited. As a result, the immune system can become dysregulated, overreacting to harmless substances and triggering allergies.
Great chance of allergies in fancy neighborhoods
According to Meelis Pärtel, many aspects of a person's living environment influence their health and the researchers tried to account for as many of those factors as possible in the new study.
"One such factor is socioeconomic status, so we were able to divide Tartu into very different areas based on property values. We didn't have direct data on each family's income, but where people live serves as an indirect indicator," Pärtel explained, describing the study's methodology.
"Our original assumption was that people living in wealthier neighborhoods might have more opportunities to go hiking and spend time in green spaces, which would mean a lower risk of allergies. But the results were the opposite of what we expected. The more expensive the neighborhood, the greater the risk of allergies," he said.
According to Pärtel, there may be several explanations, but lifestyle is likely a key factor.
"People living in more expensive neighborhoods tend to drive more and walk less. Clothes are kept cleaner, children are discouraged from getting muddy and that's probably where the connection with wealthier neighborhoods comes from," Pärtel said.
Biodiverse kindergarten yards
Pärtel said the findings are particularly valuable for urban planners because they clearly demonstrate the irreplaceable role of urban nature in creating healthy living environments. For example, when designing playgrounds, planners should ensure they are not made up entirely of artificial materials.
"Over the course of our long evolutionary history, we've adapted to the bacteria found in nature. That's why our living environments should be much more natural, with more plant species and more soil. Then we're in our natural environment and our health is better," he said.
The study also found encouraging results from samples collected at Tartu preschools. "On average, Tartu preschools had an even greater diversity of gammaproteobacterial species than ordinary green spaces, while private gardens fell somewhere in between. That's certainly good news for parents in Tartu because it suggests that preschool environments generally provide the kind of microbial exposure that can support children's immune systems," Pärtel said.
The researchers plan to continue studying the links between biodiversity and the immune system. Their next step will be to focus on specific green spaces.
"Since we found that microbial biodiversity benefits health, but also that it varies across the city, with some green spaces being far more biodiverse than others, the next question is whether we can somehow increase microbial biodiversity," Pärtel explained.
The full study has been published in the journal Urban Forestry & Urban Greening.
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Editor: Marcus Turovski
