Researchers from the University of Helsinki, the Natural Resources Institute of Finland and the University of Tampere have demonstrated that indoor gardening can increase bacterial diversity on the skin and boost levels of anti-inflammatory molecules in the blood. Their findings are published in the journal Environment International.
As part of his doctoral thesis, Mika Saarenpaa from Helsinki investigated how city dwellers' health, particularly their exposure to immune-modulating microbes, can be easily increased through meaningful activities integrated into daily life. According to Saarenpaa, urbanization has led to a considerable increase in immune-mediated diseases such as allergies, asthma and autoimmune diseases because we live so “clean” in cities.
Knowing from previous research that exposure to naturally occurring, microbial-rich materials can alter the human microbiome, Saalenpaa had his study subjects engage in urban gardening for a month: the experimental group used a growing medium with high microbial diversity that mimicked forest soil, while the control group used a peat-based medium with fewer microbes.
“One month of indoor urban gardening increased bacterial diversity on the skin. [experimental] “This was associated with increased levels of anti-inflammatory cytokines in the subjects' blood,” Saalenpaa said. In contrast, no changes were observed in the blood or skin microbiome in the control group. This suggests that peat, the world's most widely used growing medium and a major contributor to greenhouse gas emissions, does not confer the same health benefits as media that mimic diverse forest soils.
“We know that urbanization reduces exposure to microbes, alters the human microbiome and increases the risk of immune-mediated diseases,” Saalenpaa said. “This is the first time we've been able to demonstrate that meaningful, natural human activities can increase the diversity of the microbiome in healthy adults and simultaneously contribute to regulating the immune system.”
Saarenpaa's study shows that microbial exposure can be easily and safely increased in the home with only a small investment of space and money. Gardening took place in ordinary flower boxes, with cultivated plants such as peas, beans, mustard and salads taken from store shelves. Although the changes were observed in just one month, study subjects enjoyed gardening so much that many said they would continue this activity and switch to outdoor gardening in summer.
“It remains to be seen how long the observed changes in the skin microbiome and anti-inflammatory cytokines will last, but we suspect that as gardening becomes a hobby, the modulation of the immune system becomes more and more persistent,” Saalenpaa said.
Zahlemper said that immune regulation by microbes can reduce the risk and even symptoms of immune-mediated diseases, and that if we can increase exposure to health-promoting microbes at the population level, we can reduce medical costs related to such diseases and improve quality of life. He said that because immune system development is most active during childhood, it is particularly important to provide opportunities for children to be exposed to nature and microbes, and suggested introducing planter boxes filled with soil rich in microbes to kindergartens, schools, and hospitals, especially in densely populated urban areas.
“My research highlights that our health depends on natural diversity, especially soil diversity,” he said. “We are one species among other species, and our health depends on the diversity of other species. Ideally, urban areas would also have diverse natural environments, so that exposure to health-beneficial microbes would not have to be sought from specially designed products.”
Image courtesy of Mika Saarenpää.
