In addition to producing healthier plants,
Living soil makes you healthy and happy
British scientist David Strachan first proposed the controversial "hygiene hypothesis" in 1989, suggesting that in our modern, sterile world, lack of exposure to microorganisms in childhood was leading to impaired immune systems and higher rates of allergies and asthma. Researchers have since refined that theory, suggesting that it is not lack of exposure to disease-causing germs at play, but rather lack of contact with "old friends" -- beneficial microbes in soil and the environment that we have long lived with -- and that mental health is also impacted.
"The idea is that as humans have moved away from farms and an agricultural or hunter-gatherer existence into cities, we have lost contact with organisms that served to regulate our immune system and suppress inappropriate inflammation," said
Christopher Lowry, senior author and Integrative Physiology Professor University of Colorado, Boulder.
"That has put us at higher risk for inflammatory disease and stress-related psychiatric disorders.
His study, showing that injecting a beneficial bacterium (
Mycobacterium vacca
),into mice can make them more resilient to stress, has been named among the “top 10 advancements and breakthroughs” of 2016 by the nation’s leading non-governmental funder of mental health research. The bacteria, when injected into mice, activate a set of serotonin-releasing neurons in the brain—the same nerves targeted by Prozac. They are also studying the effects on post-traumatic stress disorder (PTSD).
His lasted findings (2019) help explain exactly how this works.
A novel lipid, or fatty acid, called 10(
Z
)-hexadecenoic acid was found in this bacteria (which is found in healthy soils).
Using
next-generation sequencing techniques they studied how it interacted with macrophages, or immune cells, when the cells were stimulated.
They discovered that inside cells, the lipid acted like a key in a lock, binding to a specific receptor, and inhibiting a host of key pathways which drive inflammation. They also found that when cells were pre-treated with the lipid they were more resistant to inflammation when stimulated.
"It seems that these bacteria we co-evolved with have a trick up their sleeve," said Lowry. "When they get taken up by immune cells, they release these lipids that bind to this receptor and shut off the inflammatory cascade.” This potential health benefits of this natural regulation for inflammation cannot be overestimated, just as described above with infection response.
Another study conducted in 2017-2018 revealed that a second substance produced by
Mycobacterium vaccae
, lysate, may prevent the development of atopic dermatitis symptoms when applied topically.
Mycobacterium vacca
bacterium is a nonpathogenic species of a family of bacteria that lives naturally in soil.
It was first discovered on the shores of Lake Kyoga in Uganda in the 1970s by immunologist John Stanford after recognizing that people who lived in the area responded better to certain leprosy vaccines. They later realized that the bacterium, found in the lakeshore soil and eventually isolated from cow dung, had immune-modulating properties that were enhancing the vaccine’s efficacy.
Research areas being pursued with regard to killed
Mycobacterium vaccae
vaccine include immunotherapy for allergic asthma, cancer, depression, leprosy, psoriasis, dermatitis, eczema and tuberculosis.
Lung cancer patients who were injected with killed
M. vaccae reported better quality of life and less nausea and pain.
THE MEANING
The results so far suggest that simply inhaling
M. vaccae
-- you get a dose just by taking a walk in the wild or
rooting around in the garden
--
could help elicit a jolly state of mind. “You can also ingest mycobacteria either through water sources or through eating plants -- lettuce that you pick from the garden, or carrots,” Lowry says.
Graham Rook, an immunologist at University College London and a coauthor of the paper, adds that depression itself may be in part an inflammatory disorder. By triggering the production of immune cells that curb the inflammatory reaction typical of allergies, M. vaccae may ease that inflammation and hence depression. Therapy with M. vaccae—or with drugs based on the bacterium’s molecular components—might someday be used to treat depression. “It’s not clear to me whether the way ahead will be drugs that circumvent the use of these bugs,” Rook says, “or whether it will be easier to say, ‘The hell with it, let’s use the bugs.’”
For now, the best we can do is breathe in the wonderful smell of healthy, living soil.
