Soil health and human health

Cristina Dumitrescu, lecturer of Ayurveda AMN-Romania

The life of man is intimately linked to that of the earth

In the past, human life was intimately related to the land; civilisation has taken many of us away from it. We live in concrete dwellings, walk on asphalt, eat food grown in soil degraded by the practices of intensive agriculture and chemical fertilization, fungicides, herbicides, pesticides, food treated in warehouses and supermarkets, pasteurized, irradiated, sterilized.
Lately hydroponics has developed, plants are grown without soil, in a watery environment enriched with selected nutrients. Soil is often seen as dirt and a source of pathogenic bacteria. The effects of this attitude can be seen, human health is deteriorating, and more and more studies are highlighting the beneficial role of contact with soil, and the saprophytic 'good' soil bacteria on human health, and how their absence can make us sick.
A multitude of bacteria live in the human body, most of which live in the digestive tract. Of these, the focus has long been on Lactobacilli, but recently it has been discovered that bacteria known to inhabit the soil are also part of the gut flora of healthy humans, or that fragments of their DNA, transferred to resident bacteria in the human gut during transit through the digestive tract, may have beneficial effects. The human digestive tract1 is colonised by up to 100 trillion microbes that have more than 100 times more genes (microbiome) than those present in the human genome. These microbes serve important functions, including additional energy production (otherwise inaccessible to humans) by degrading soluble fibres, synthesising vitamins such as biotin, folic acid and vitamin K, metabolising xenobiotics such as heterocyclic amines, preventing colonisation by pathogens, and contributing to the development of a mature immune system.
These saprophytic bacteria are affected by antibiotics. Antibiotics can be abused, in many countries (including Romania) they are used excessively in humans, against the recommendations of medical guidelines (with a direct effect on the bacteria in the digestive tract of those who use them), but also in animal husbandry. These antibiotics partially or completely transformed after passing through organisms (human or animal), as well as residues from the drug industry (in the past less regulated) end up in water and soil, changing the balance of bacteria in them. Several aspects are related to soil health, and will be developed further: gut flora, food quality and assimilation, prevalence of allergies and asthma, protection against infections, mental health.

Gut flora and body health

Raúl Ochoa-Hueso2 (from the Department of Ecology of the Autonomous University of Madrid) points out the similarity and deep connections between the state of the human gut and the health of the underworld. He makes a comparison between "healthy and unhealthy intestines" and points out some health problems associated with "unhealthy intestines".
Thus the "healthy gut" has a more abundant and varied gut flora, which synthesises essential nutrients and beneficially influences the immune system; an "unhealthy gut" has a less diverse flora, and contains more pathogenic varieties.
A 'healthy gut' is less prone to infection due to competition for nutrients and increased detoxification capacity, and is associated with general well-being. On the other hand, an 'unhealthy gut' is associated with joint and muscle pain (acidity resulting from metabolism playing its part), digestive and skin disorders. Similarly, in terms of the environment, bio-diversity (microbes, fauna and plants) is remarkably superior in healthy ecosystems.

Food quality and assimilation depends on the soil

Daphne Miller3, family physician and associate professor at U.C. San Francisco, has noted the influence of soil on patients' health. Thus she extends the words of Hippocrates "let food be your cure", pointing out that the soil in which it grows can provide the true cure. Citing the results of studies conducted at Washington State University using DNA sequencing technology, she concludes that soil that supports a wide diversity of life tends to produce food that is much richer in nutrients.
The author also cites a group of French microbiologists who detected DNA sequences specific to bacteria living on algae that were transferred to microbes residing in the intestines of Japanese. The result is that the Japanese have thus become much more capable of extracting nutrients from algae. Similarly, exposure to bacteria in the soil could enhance the assimilation of nutrients from food.

Microbes against allergies

The same author3 mentions studies by European immunologists and allergists on the so-called "farm effect". Children raised on organic farms have a significantly lower rate of allergies and asthma compared to children raised in cities or on industrialised farms. One theory is that early exposure, even intrauterine, to a variety of microbes impacts the modulation of the immune response. Another hypothesis is that microbes resident in the human body are a "first line of defence" for our immunity. Newer research suggests that there is a continuous exchange of microbes between the soil and the gut, which would be behind this "farm effect".
Other researchers cited by Zoë Schlanger4 have noted an increased rate of allergies in children without Helicobacter pylori in their stomachs, and also this bacterium would provide some level of protection against gluten intolerance.
Jef Akts5 cites the Karelia experiment, conducted by Finnish immunologists, which supports the same observation. They found that children in the country have more Acinetobacter bacteria on their skin, and have more leukocytes in their blood that produce the anti-inflammatory cytokine IL-10, suggesting that this bacterium induces a modulatory effect on the immune system. Another team, led by Fyhrquist, found more Bacteroidetes phylum than Firmicutes phylum (bacteria associated with asthma and inflammation in both mice and humans) in the intestines of mice exposed to soil.
Animals exposed to soil also had a higher amount of anti-inflammatory proteins that modulate the immune system, including the enzyme A20 which has been shown to protect against asthma in mice.
Even exposure to small amounts of airborne soil would be beneficial, says Martin Breed (Flinders University in Adelaide, Australia). Mice exposed to amounts of soil up to 100-1000 times smaller than in other studies developed changes in the microbiome and scored lower on stress tests, suggesting beneficial effects of time spent in nature.

Protection against infection

Ian Pepper and Charles Rice6, describing the influence of soil on public health, mention substances present in soil such as antibiotics like streptomycin (synthesised by the soil organism Streptomyces griseus). Thus the majority of antibiotics and anti-tumour drugs approved at the end of the last century originate or are inspired by natural products, many of which are also present in soil.
We add that a rich and varied gut flora can protect against infections with pathogenic bacteria simply by competing for space and food sources.

Mental health

The Medical News Today7 newsletter published an article written by Ana Săndoiu about the beneficial influence of biodiversity on mental health through gut bacteria. She quotes Craig Liddicoat (University of Adelaide, Australia) who conducted a randomised experiment on mice, and observed that exposure to biodiverse soil led to changes in their gut flora. The bacterium Kineothrix alysoides produces butyrate, a short-chain fatty acid with numerous digestive and cardio-metabolic health benefits. Exposure to this soil bacterium resulted in reduced anxiety-like behaviour in most anxious mice.
According to this researcher, the results suggest that biodiverse soils are an important source of butyrate-producing bacteria for replenishing the mammalian gut microbiome, with potential benefits for digestive health and indirectly for mental health.
Zoë Schlanger4 writes about the antidepressant effects of soil microbes. She begins by citing a study by oncologist Mary O'Brien, who injected patients with the harmless soil bacterium Mycobacterium vaccae and achieved a significant improvement in their quality of life. Patients became happier, more vital, and with improved cognitive function, benefiting from the reduced emotional impact of late-stage cancers. The same bacteria injected into mice by the team led by Lowry resulted in the activation of neurons that produce serotonin, a neurotransmitter whose deficiency causes depression.
In addition, neurons involved in the immune response were activated, suggesting a close link between the immune system and emotional health. The injected mice showed lower levels of anxiety and stress (maze test), while reducing inflammation in the colon (observed in stressed mice). They were also less stressed about subordinate relationships and exhibited less docile, submissive behaviour, developing a pro-active rather than passive stress response.
Tom Olijhoek8 starts an article quoting the book "Follow your Gut" written by Rob Knight, and shows interest in a topic developed in chapter 4. Administration of Bacteroides fragilis to mice with autism-like symptoms resulted in a reduction in some of the gut symptoms and cognitive deficits specific to autism. Tom Olijhoek goes on to cite other studies that have shown that pro-biotics composed of several species can be used as a strategy to prevent depression.

References

1. Cindy D. Davis, Ph.D, The Gut Microbiome and Its Role in Obesity, Nutr Today. 2016 Jul-Aug; 51(4): 167-174.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5082693/
Raúl Ochoa-Hueso, Global Change and the Soil Microbiome: A Human-Health Perspective, Front. Ecol. Evol, 06 July 2017. Accessed on 9 June 2020 at
https://www.frontiersin.org/articles/10.3389/fevo.2017.00071/full
3. Daphne Miller, The Surprising Healing Qualities... of Dirt, online publication Our World, United Nations University, accessed 9 June 2020 at
https://ourworld.unu.edu/en/the-surprising-healing-qualities-of-dirt
4. Zoë Schlanger, Dirt has a microbiome, and it may double as an antidepressant, May 30, 2017, accessed June 9 on the Quartz website at the link:
https://qz.com/993258/dirt-has-a-microbiome-and-it-may-double-as-an-antidepressant/
Jef Akst, The Influence of Soil on Immune Health, 8 January 2020, in The Scientist, accessed 9 June 2020 at link:
https://www.the-scientist.com/news-opinion/the-influence-of-soil-on-human-health-66885
6. Ian Pepper and Charles Rice, The Influence of Soil on Public Health, 2010 19th World Congress of Soil Science, Soil Solutions for a Changing World 1 - 6 August 2010, Brisbane, Australia. accessed on 9 June 2020 at the link
https://www.iuss.org/19th%20WCSS/Symposium/pdf/2341.pdf
7. Ana Săndoiu, Biodiversity may benefit mental health by affecting gut bacteria, Nov 2017, Medical News Today, accessed 9 June 2020 at link:
https://www.medicalnewstoday.com/articles/326937
8. Tom Olijhoek, Relation between human microbiome and disease conditions including psychological disorders, ScienceOpen Research, (2015), accessed 9 June 2020 at link:
https://www.scienceopen.com/collection/455dee40-2744-4713-b0ef-fdd650aaacd4