Urban gardening may improve human health

A collaborative study between the University of Helsinki, Natural Resources Institute Finland, and Tampere University demonstrated that a one-month indoor gardening period increased skin bacterial diversity and was associated with higher levels of anti-inflammatory molecules in the blood.

In his doctoral thesis, Mika Saarenpää explored how microbial exposure that enhances urban residents’ health and immune regulation could be increased through everyday activities. Previous research has shown that contact with nature-derived, microbially rich materials alters human microbiota. In Saarenpää’s study, participants engaged in urban gardening, a natural activity for them, which may lead to long-term changes in immune system functioning.

“One month of urban indoor gardening boosted the diversity of bacteria on the skin of the subjects and was associated with higher levels of anti-inflammatory cytokines in the blood. The group studied used a growing medium with high microbial diversity emulating forest soil,” says Saarenpää from the Faculty of Biological and Environmental Sciences at the University of Helsinki.

In contrast, the control group used a microbially poor peat-based medium and saw no changes in blood or skin microbiota. Peat, the most widely used growing medium globally, has a significant negative environmental impact and does not offer the health benefits of a medium mimicking diverse forest soil.

Saarenpää highlights the significance of these findings, as urbanization has led to a rise in immune-mediated diseases such as allergies, asthma, and autoimmune diseases, resulting in high healthcare costs. “We live too ‘cleanly’ in cities,” he notes. Urbanization reduces microbial exposure, alters human microbiota, and increases the risk of immune-mediated diseases. This study is the first to show that meaningful and natural human activities can enhance microbiota diversity in healthy adults and contribute to immune system regulation.

Urban gardening is an effortless way to improve health. Microbial exposure can be increased easily and safely at home throughout the year with minimal space and financial investment. In the study, gardening took place in regular flower boxes with plants like peas, beans, mustards, and salads bought from stores. Changes were observed within a month, and many participants enjoyed gardening so much that they planned to continue and switch to outdoor gardening in the summer.

Saarenpää explains that microbe-mediated immunoregulation can reduce the risk of immune-mediated diseases or even alleviate their symptoms. Increasing health-promoting microbial exposure at the population level could lower healthcare costs and improve people’s quality of life. “We don’t yet know how long the changes in skin microbiota and anti-inflammatory cytokines last, but if gardening becomes a hobby, it can be assumed that immune system regulation becomes more continuous,” he says.

Saarenpää emphasizes the importance of exposing children to nature and microbes, as the immune system is most active during childhood. Planter boxes filled with microbially rich soil could be introduced in kindergartens, schools, and hospitals, especially in densely built urban areas. To ensure health benefits without risks, it is essential that the skin on the hands remains unbroken and that dusty growing media are not inhaled.

Saarenpää concludes, “My research highlights our health’s dependence on the diversity of nature, particularly soil. We are one species among many, and our health relies on the diversity of other species. Ideally, urban areas would have a diverse natural environment that provides beneficial microbial exposure without the need for specially designed products.”

Source: Science Daily