Biodiverse soils … when the right kind of dirt may be good for you

Around the world, more and more people are living in cities, while our contact with natural biodiversity and soil is declining. At the same time, we have seen a rapid rise in rates of allergies, auto-immune and chronic inflammatory diseases. Now researchers are finding accumulating evidence that these two major trends may be linked, in a new paper published in Science of the Total Environment.
A possible explanation for the modern pandemic of immune-related disease is that, put simply, our immune systems are losing their fitness. From evolution, our bodies are designed to cope with exposure to diverse environmental microbiomes coming from biodiverse plants, animals and soils. Environmental microbiomes are believed to help supplement the protective human microbiome inhabiting our skin, airway and gut, and they may also play a role in immune signalling, for example, helping to build tolerance to normally harmless substances.
Microbes are everywhere in nature, and modern science tells us that the vast majority of microbes don’t cause illness. With the possibility that some types of environmental microbiomes may actually benefit our health, this represents a potentially important connection between people and nature. If we can build knowledge of such a connection, it may be possible to reduce our rising population health costs through new approaches to nature-based public health programs and better designs for urban green space. The thinking is that greater exposure to biodiverse green space and soils may build diversity in the human microbiome, which in turn is linked to improved immune function and health.
In recent research, led by PhD Student Craig Liddicoat in Science of the Total Environment a team from the Environment Institute tested the idea that soil exposures may benefit human health at the population-level. The paper included Environment Institute researchers, Professor Peng Bi, Professor Michelle Waycott, Dr Martin Breed, and Professor Philip Weinstein.
The team compared rates of infectious and parasitic disease across regional Australia with mapping of soil cation exchange capacity (CEC), a surrogate for soil microbial diversity. They found where neighbouring soils were high in CEC (i.e. typically higher soil biodiversity), this was associated with significantly lower disease risk, particularly in lower socioeconomic areas. Also, prediction models for disease risk in unseen (test) areas were significantly improved when knowledge of the soils was included.
The study has strengthened support for the idea that better quality soils, and biodiverse microbial communities from the environment, may boost immune-related health. Synergies may also be possible, where efforts to protect and enhance soil biodiversity in conservation, agriculture or urban green space, may offer cost-effective human health co-benefits.
Further research is underway to test possible mechanistic links between soils and their microbiomes, and the health of exposed populations.
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