Nearby green spaces with diverse soil bacteria lower children’s allergy risk

A study by researchers at the University of Tartu and the Estonian University of Life Sciences has found that children are significantly less likely to develop allergies later in life when diverse soil bacteria are present in green spaces near their homes, ERR reports.

The researchers found that when a green space with a rich bacterial community was located more than approximately one kilometre from a child’s home, the child’s risk of developing allergies increased noticeably.

The study began during the coronavirus pandemic, when the researchers were unable to travel abroad to collect samples for a larger project. Instead, they gathered 743 samples from green spaces in Tartu. According to Meelis Pärtel, a botany professor at the University of Tartu, this made Tartu one of the best-mapped cities in the world for soil microbes.

“The most exciting finding of the study was that we identified one specific group of environmental bacteria whose diversity was associated with children’s allergy risk. The greater the diversity, the lower the risk of developing allergies,” Pärtel said.

The group in question is gammaproteobacteria, which includes a wide range of microbes living in environments from the seabed to the human intestine. Some bacteria in the group cause salmonella and bloody diarrhoea, while others produce vitamin K in the gut and prevent disease-causing organisms from taking hold.

Pärtel said it was not yet fully clear why diversity within this group had the strongest association with allergy risk. One possible explanation is that the group includes disease-causing bacteria, forcing the immune system to learn to distinguish between harmful and harmless organisms.

For the study, the researchers also analysed health data from 148 children born in Tartu. Comparing the data with the soil samples showed that the risk of developing allergies rose considerably when a green space with a rich bacterial community was more than approximately one kilometre from the child’s home.

Humans have evolved alongside natural environmental bacteria. Regular contact with microbes helped the immune system distinguish genuinely dangerous organisms from harmless intruders. In today’s carefully maintained urban environments, however, this contact can be limited. This may contribute to immune system disorders in which the body reacts too strongly to harmless substances, causing allergies.