Is Soil an Antidepressant – Does it Make You Feel Good?

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Robert Pavlis

The meme pictured below has been making the rounds on social media and it gets quick acceptance by readers. As gardeners we all know that being in the garden or going for a walk in nature makes us feel good. Finally science agrees with us and has even found the root cause for these feelings of euphoria: serotonin.

People agree with the meme quickly because it supports their exiting beliefs but they have no basis for their existing beliefs.

But let’s face it – a meme is not scientific proof. What does the science really say?

Is Soil an Antidepressant - Does it Make You Feel Good?
Is Soil an Antidepressant – Does it Make You Feel Good?

Analyze the Data

When you are confronted with new information like the above meme, take a moment and evaluate it. Do a sniff test to see if it could be valid information.

A quick Google search shows that Mycobacterium vacii does not exist. However, Mycobacterium vaccae does exist. One red flag.

Antidepressant is spelled wrong – second red flag.

How can the smell of bacteria make us feel good? Very suspect to me.

Serotonin and Feeling Good

Serotonin has been well studied and is known as the “feel-good hormone”. It plays a key role in staving off anxiety and depression. So if smell from microbes in soil cause higher levels of serotonin, it is quite likely that these smells make us feel good.

Food Science for Gardeners, by Robert Pavlis

Petrichor

Petrichor is the pleasant smell that frequently accompanies the first rain after a long period of warm, dry weather. Humans are quite sensitive to this smell which is caused by a chemical called geosmin and it has been reported that humans can detect 100 parts in a trillion. We find this smell quite pleasant and geosmin has even been added to perfumes.

Geosmin is made by Streptomyces bacteria. It is not an antibiotic but it does attract insects that then help distribute spores of Streptomyces?

The important point for our discussion is that we now know we can smell compounds made by bacteria in soil. But M. vaccae is not Streptomyces.

Mycobacterium vaccae and Cancer

Mycobacterium vacii
Mycobacterium vaccae, credit: CU Bolder Today

Mycobacterium vaccae is in the same genus as Mycobacterium tuberculosis, the bacterium which causes tuberculosis. Numerous trials have indicated that exposure to oral and injectable products derived from M. vaccae bacteria can have positive effects in treating tuberculosis. This prompted a doctor named Mary O’Brien to give the bacteria to lung-cancer patients to see if it might improve their condition. What she found was that it made them feel better and have less pain.

Mycobacterium vaccae and Serotonin

Other scientists followed up on this work and slowly deduced the chemistry involved.

Rats that were fed M. vaccae showed less anxiety and improved learning for running mazes.

When rats were injected with M. vaccae they showed less stress and aggravation following tail shock treatments.

Injection in mice activated serotonergic neurons and caused antidepressant-like behavior.

Dr. C. A. Lowry has done a number of studies to clearly show that M. vaccae does cause an increase in serotonin levels.

Scientific Proof Or Not

So far I have presented some of the science that has lead to the conclusions in the meme and hundreds of other popular articles have made similar claims. It seems like a clear connection. A bacterium in soil causes our bodies to make more serotonin which in turn makes us feed good. Even online magazines like Medical News Today got swept up in the excitement and announced, “friendly bacteria found in soil may affect our brain in a similar way to antidepressants. ” They at least included the all important word “may”, most articles fail to do that.

Microbe Science for Gardeners Book, by Robert Pavlis

But here are the problems with this conclusion.

  1. All testing that showed an increase in serotonin levels has been on rats and mice.
  2. The bacteria were either injected or fed to the test animals.

I have found no testing on humans that showed a change in serotonin levels after exposure to M. vaccae. I have also not found testing that looks at the effect of “smelling” the air from soil.

It is quite likely that we breathe in some bacteria spores as we work in the garden or walk in the woods, but the amount is probably very small compared to the amounts injected during the studies.

This type of unsubstantiated leap from some scientific facts to a conclusion is very common in news reporting. I think it’s because the facts alone don’t make sensational headlines. This leads to completely inaccurate conclusion like this one:

“Working in the garden, or even taking a walk in the woods can provide enough of a dose of Mycobacterium vaccae to uplift you.”

Or this one:

“Getting your hands dirty in the garden can increase your serotonin levels.”

Neither is supported by science but they do help spawn a new myth.

Shit Might Work Better Than Soil?


The gastrointestinal tract is rich in microbe-generated signaling substances that affect several biological functions in the body (‘inter-kingdom communication’). “The normal smell of human feces is largely due to indole, one of the major metabolites of tryptophan. Tryptophan is an essential amino acid that is used to produce serotonin which has garnered much attention because of its wide physiological and clinical implications.”

The science supporting this meme is at least as strong as the science supporting the meme at the top of this post.

Soil Can Make You Sick

Before you go breathing in soil or even eating it, you should know that soil, compost and potting media can make you sick. Find out more at Soil Borne Diseases – Does Soil Make You Sick?.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

13 thoughts on “Is Soil an Antidepressant – Does it Make You Feel Good?”

  1. It’s really important for each of us to read the studies on our own; we may be missing context and content when we just read someone’s understanding of a study.

    Researcher Christopher Lowry, who leads these studies, participates in and encourages camping and other nature related activities. He also mentions benefits of rural lifestyles. The aforementioned don’t have anything to do with taking injections, but have everything to do with being closely aligned with the outdoors. But not all people can have, or even want to have, this lifestyle; and let’s face it, many would rather take a pill or vaccine to provide these effects.

    Here are some quotes attributed to Christopher Lowry:

    “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 Lowry. “That has put us at higher risk for inflammatory disease and stress-related psychiatric disorders.”

    “As human societies have migrated to urban environments, we have lost touch with a host of bacterial species that play a role in regulating our immune system, and this is helping to fuel an epidemic of inflammatory disease,” says Lowry. “I want to know: What are the impacts on mental health?”

    Reply
  2. Though this may be true, early on in my aquaponics experience, I found it ‘ therapeutic ‘. Coming from someone who’s never grown anything in his life.

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  3. I had an old friend who was a passionate gardener and garden writer. She told me once that when she saw a freshly plowed field, she had an urge to go out and roll around in the beautiful soft soil.

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  4. Hi Robert, Great article! I hadn’t seen the meme, but I’m glad to learn the science you presented here. One of the problems I see with this type of popularized inaccurate “science” is the risk that genuine science is tarred with the same unreliable brush. Anyway, I don’t need science to tell me I enjoy working with soil and getting my hands dirty. And if someone doesn’t enjoy it already, a meme isn’t going to change that.

    Reply
  5. I believe that getting out and working in the garden can make one feel better, but I don’t think it has anything to do with smell. Rather, I believe it has to do with sun exposure, even filtered sun on a cloudy day. Many people, including me, are affected with Seasonal Affective Disorder, or SAD, a type of depression that is often treated with light exposure, especially from the sun. Getting out in the yard or garden always make me feel much better, or any activity outdoors. However, I do like the smell of good soil.

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  6. Interesting post Thanks for educating. The research quoted seems to have been carried out in Temperate climates. Any findings in soils in Tropical countries?

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    • LOL you mean like how medical masks even say in the small print not protective against viruses,i work in filtration the micron rating of any mask is wholly inadequate the only guarantee is a seperate air supplied respirator or a sealed polyethylene bag or walk around in a NBC suit…………………

      Reply
  7. Awesome
    I came across that meme earlier and it made me laugh.
    Thanks for your good analyzation, especially the poop part. Next season I’ll try the poop and garden simultaneously method.

    Reply

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