Playing in the Dirt vs. Antidepressants

Exposure to friendly soil bacteria may be just as effective as antidepressant drugs, a new study suggests.

Researchers from the University of Bristol in the UK found that certain soil bacteria may improve mood by boosting the immune system.

In the study, mice were exposed to a harmless soil microbe called Mycobacterium vaccae and then performed a behavioral task commonly used to test the efficacy of antidepressant drugs. The mice were placed in a large beaker of water for five minutes and watched to see how long they continued swimming and searching for an exit before giving up. The researchers found that the bacteria-exposed mice continued paddling around much longer than the control mice.

Mice given antidepressant drugs also appear more determined to escape, noted researchers. These results are comparable to a medical trial conducted a few years ago in which human cancer patients treated with the bacteria reported significant increases in their quality of life.

Researchers explained that while M. vaccae is no longer being pursued as a treatment for cancer because it didn't prolong life, patients did report increases in things like vitality and cognitive function and decreases in pain.

The researchers suggested that the microbes affect the brain indirectly by causing immune cells to release chemicals called cytokines, which may activate the nerves that relay signals from the body to the brain.

The stimulated nerves cause certain neurons in the brain to release a chemical called serotonin into the prefrontal cortex, an area of the brain known to be involved in mood regulation, among other things. A lack of serotonin in the brain is thought to cause depression in people.

Researchers concluded that the new finding take this idea, called the "hygiene hypothesis," a step further suggesting bacteria-exposure not only boosts the immune system, but also alters vulnerability to conditions such as depression as well.

For more information about integrative therapies for depression, please visit Natural Standard's Comparative Effectiveness database.

Comments

[Anonymous]

It seems like what the bacteria are doing is stimulating cytokines in order to trigger some sort of immune response that makes the person go into 'defense mode.' Theoretically, it does seem to make some sense, but more studies should be done with humans, not mice. Also, comparing mice exposed to M.vaccae vs. antidepressant-treated mice doesn't seem appropriate. One would trigger more of an immune response vs. an increase in serotonin (mood). Antidepressants take more than a month to start working, so I'm curious as to how many hours the mice had to spend outdoors on M.vaccae enriched soil.

[Matthew]

Great find! It's supportive of an idea that I've believed for some time - and it's that humans are overly concerned with the elimination of microbes from their immediate space. Indeed, reducing the numbers of pathogenic microbes is a great idea. However, perhaps elimination of all microbes isn't such a great idea, this being more evidence.

An interesting paper just came out (PMID: 17289307), and it did a nice job explaining the symbiosis that exists between animals - including humans and microbes. From the abstract:

"Bacteroides thetaiotaomicron mediates the maturation and function of the gastrointestinal tract in several different ways. Similarly Bacteroides fragilis directs the development of the immune system both in and outside the gastrointestinal tract."

There was also a good paper in the Annals of Neurology not too long ago (PMID: 17230481). Too make a long story short, noting that the instance of multiple sclerosis (MS) increased with decreasing instance of parasite infection, the study examined the relationship between parasite infection and (MS).

The authors of this study believe that their findings support that an autoimmune response resulting as a consequence of a parasite infection may result in a decrease in the inflammatory response associated with MS. The authors further note that evidence for production of cells that inhibit the immune response in parasite infection is now emerging, providing a mechanism by which infected hosts exhibit an altered immune response.

In conclusion, the authors note that "induction of a regulatory anti-inflammatory network generated by persistent parasite infections may offer a potential explanation for environment-related suppression of MS development in areas with low disease prevalence."

Pretty cool. I guess the take home message is to let your kids play in the dirt, and less microbes does not necessarily equal greater health.

[Jen]

I also find this study very interesting. Researchers at Georgetown University Medical Center recently found out that serotonin can trigger an immune response. This suggests that serotonin may help boost the immune system in patients who are depressed and susceptible to infections.

[J. Kathryn Bryan]

I doubt that members of the American Horticultural Therapy Association would be surprised at the results of this study.

I recently did a lot of research about constructing a terrarium. I found a lot of great information on Web sites and message boards dedicated to living with disabilities and disability rights. I love the idea of gardening as a means of personal enrichment and sensory stimulation.

Besides, playing in the dirt is fun.

[Leah Cohen]

I agree that exposure to bacteria, especially non-pathogenic bacteria, might be overlooked today. Clearly, the benefits of hygiene in healthcare cannot be overstated. However, at the same time, it is important to note the potential benefits of exposure to symbiotic organisms such as that of the human digestive tract and skin, which are common targets for broad spectrum anti-bacterials.

Regarding the benefits of outdoor activities, they have their own benefits in their own right, and underscore the importance of reforestation, urban gardening programs, and city tree planting initiatives. There is actually a really informative article in National Geographic on the Paris parks initiative, and the role of city green space in community well-being and psychological health (http://www7.nationalgeographic.com/ngm/0610/feature3/index.html).

[D. B. Martin]

I concur with others that this study demonstrates the intricate, interactive relationships among organisms and the infinite "intelligence" of the natural world.

In recent years, we have been nearly terrorized into thinking we must disinfect everything we touch, eat or breathe. This not only prevents us from forming natural immunity, but it also interferes with many other natural processes, such as the one described in this study, that we are not even aware of. While a reasonable degree of hygiene is important, it has been taken to extremes in recent years. With the proliferation of antibacterial soaps, dish liquids, counter wipes, cleansers (etc.), we greatly increase the risk of creating resistant bugs, while "washing away" many known and unknown benefits of friendly bugs in our environment.

[Cady B]

Once again, a study showing the value of the natural world. Natural foods are healthier than processed foods. Increasing evidence suggests that simple bacteria and simple things like art and music therapy and even gardening are non-medicinal ways to improve symptoms of depression.

There hasn't been a head-to-head study with antidepressants and this bacterium to show the difference in efficacy or difference in adverse events. I would like to see more information come out in the future regarding alternative therapies, such as this one, in comparison to the drugs that are so widely prescribed these days.

[Rachelle Provost]

Wow, thank you Matthew and DB Martin!!! I agree, I think that it's good to get a little dirty now and then. I say that, and yet I also always carry hand sanitizer with me when I'm taking public transportation. I guess it's because I distinguish between dirt and the more "natural" bacteria found in mud and the bacteria found in public spaces that I can't help but think contains all kinds of disease-causing germs. I had a chance to travel to Tanzania, Africa, and the children there seem to have much better immunity and seemed to be HAPPIER than our children here in the U.S. - probably because all they do is play in the dirt :)

[Linda]

I have to disagree with some of you here. The bacteria, M. vaccae, is that present in all soils? The study stated that "UK found that certain soil bacteria may improve mood by boosting the immune system." How do we know the soil in our backyard has the same bacteria? Other factors need to be considered, such as parasitic diseases and viruses in soil. The study did not indicate how long the mice were exposed to this soil, and the mice were only observed for five minutes. I'm skeptical about its benefits. I would like to see more studies about this.

[Bob]

Hey, I like this article. Next time my wife says that gardening will ruin her nails and she doesn't want to get dirty, I will have a valid excuse to have her plant flowers with me! Good article!

[Larry]

I am 55 years old, and I love to garden. I have a coy pond in my backyard with six three-pound fish in it. I have flowers and plants all over my yard. I have hanging plants and potted plants as well. I always thought of gardening as my relaxing hobby that would give me a green thumb. Looks like this article says I will get more then a green thumb; I will have a brighter day!! Maybe I will talk to my doctor about stopping my Paxil prescription and garden more!

[MV]

I am curious about how exactly the microbes trigger the cytokines to activate neurons to release serotonin. Additional studies should look into the process. I think it is great that something as simple as microbes in the dirt could be effective for conditions, such depression, as well as immune system. It is amazing to think that our immune system can communicate like this with the brain.

[Emily P.]

Once again, science suggests that many cures exist in natural forms. Instead of taking chemical antidepressants, one can turn to this alternative and obviously more fun option. Antidepressants run the risk of a variety of side effects, including addiction, but playing in a little dirt never really did anyone all that much harm.

[Paul]

I am mostly concerned with the use of a mycobacterium in this study. This genus is the same one that brings us Mycobacterium tuberculosis, which I don't think many people would think of as a good bacteria. I know that sharing the same genus doesn't mean one can't be good while the other is bad, but I am concerned about their close connection, and that mycobacterium are notoriously hard to treat. I would want a little more comfort and data showing that it is truly harmless before trying anything in humans.

[donnakelli]

I've been chronically depressed for about 7 years and just started seriously gardening this year. I've noticed a real improvement in my energy level and all around sense of contentment this past spring and summer. I have been crediting the garden activity for this upswing, and now i read about this study. Could there be a real link between increased cases of depression in U.S. and the extreme estrangement from the land that we experience? I believe that if more people would tear out their useless lawns and get digging and growing plants that provide some benefit either by becoming food, herbal/medicinal, visual beauty or other esoteric quality that can be appreciated, we as a people would be much happier and less stressed. Plus, having a garden means having other living things around too, like bees, butterflies, spiders, ants, hummingbirds, etc. I live in the Midwest, and I have realized that 5 1/2 months of growing season is not enough for my emotional and mental health!