Happiness Comes From…Dirt?

Hey, everyone!

So, May is finally here! For many of us, that means our schedules are clearing up so that we have more time to get out and enjoy the outdoors. The possibilities for outdoor fun seem endless: hiking, swimming, camping, gardening, biking, running, outdoor yoga….Whatever it is you do, I bet you’re happy doing it-and not just because it’s fun. Many of us have heard of runners high and are aware of the positive effects of vitamin D, but what if I told you that those factors aren’t the only ones that contribute to a happier disposition? What if I said that there might be an extra factor that can be found in dirt? According to experimental research, symptoms of depression and anxiety could be reduced by playing around in the dirt thanks to a little organism called Mycobacterium vaccae ( or M. vaccae for short).

Researchers Graham A.W. Rook and Christopher A. Lowry suggest that heat-killed M. vaccae could improve mood as well as anxiety-related behaviors. Their suggestion is supported by previous studies that support the hygiene hypothesis, more commonly known as “old friends.” So, without M. vaccae, our immune systems are likely to become more sensitive to pro-inflammatory illnesses like IBS, Crohn’s disease, certain cancers, and heart disease. But, how does this all relate to depression and anxiety?

Rook and Lowry cite many sources which have found correlations between high levels of pro-inflammatory cytokines and people with major depressive disorder. Of course, correlation does not imply causation. Rook and Lowry recognize how complicated depression is. However, they refer to presidential evidence that suggests cytokines can effect moods. For example, they note that cancer patients treated with certain cytokines increased depressive symptoms. Yet, when these same patients were treated with heat-killed M. vaccae, their moods seemed to improve. These findings led other scientists to conduct the forced swim test on mice injected with heat-killed M. vaccae.

What did they find? The mice that were injected with M. vaccae were more mobile than those that weren’t, which suggests that overall anxiety was lowered. What do they think is going on? The heat-killed M. vaccae targeted a certain subset of serotonin releasing neurons in the dorsal raphe nucleus (DRI) and medial prefrontal cortex of the mice by bringing down an overproduction pro-inflammatory cytokines. In sum, we might be able to vaccinate against depression.

But, we’re not going to find heat-killed M. vaccae out in the wild of our backyards. What about live M. vaccae?

That’s exactly what Dorothy M. Matthews and Susan M. Jenks wondered. Working off of Rook and Lowry’s hypothesis, Matthews and Jenks conducted several studies using male, BALB/c mice. The M. vaccae was grown in a nutrient broth at 98.6 degrees F and refrigerated at a livable temperature until needed. .1 mL of the broth were pipetted onto small chunks of white, peanut covered bread and fed to ten mice. Eight mice were fed the same white, peanut covered bread, but without the organism. The feeding methods and numbers stayed the same throughout all four experiments. The first three experiments recorded anxiety-related behaviors while the mice navigated a tri-level Hebb-Williams style complex maze with each level increasing in difficulty. The last experiment kept the same feeding process as the first three, but an elevated zero maze instead. This experiment was done to determine if anxiety-related behaviors changed during the completion of simpler tasks.

And their findings? In short, live M. vaccae seemed to produce similar effects as the heat-killed M. vaccae in Rooks and Lowry’s findings.

The first experiment showed a consistent decrease in four out of the seven anxiety-related behaviors in mice fed the live M. vaccae. In the second experiment, M. vaccae was removed completely from the experiment and those that had the M. vaccae in experiment one continued to show reduced anxiety behaviors for up to a week. The third experiment suggested that live M. vaccae improved learning in the experimental mice. Finally, the last experiment showed that the experimental mice had more head-dip behaviors than the control, which further suggests a decrease in anxiety.

However, there were some noted problems in this study. First, the mice used are already prone to high anxiety, so their brain chemistry may react differently to live M. vaccae than the brain chemistry of other mice and humans. Second, an increased familiarity with the maze may have caused the mice to remember the maze and may have reduced anxiety. Similarly, some mice were reported to have run, which may have also contributed to reduced anxiety. Lastly, the effects of live M. vaccae in a natural setting are still unknown.

Clearly, more experimentation needs to be done, especially in a natural setting. Regardless, I say get dirty! You’ll be glad you did.

Thanks for reading my article! Let us know in the comments below: Could there be negative consequences to using M. vaccae in immunizations against depression and anxiety? Do you think that too much live M. vaccae could be bad for us?