Boosting mood with…..dirt?

Whenever I’ve felt blue, I know that one sure cure is to tackle my garden. Of course, living in California makes this a year-round option. No matter what type of problem had been bothering me, I always felt better after spending some time outdoors, even if that meant yanking weeds.

Researchers at the University of Bristol and the University College London might have shed some light on my favorite mood-boosting exercise. Mice exposed to a type of bacteria commonly found in soil, Mycobacterium vaccae, acted as though they had received treatment with antidepressant medication. Apparently, exposure to M. vaccae boosted the activity of serotonergic neurons. Serotonin activity, of course, appears to be correlated with mood.

These experiments originated from observations that cancer patients being treated with M. vaccae reported improvements in well-being. Why would we use bacteria to treat cancer? Apparently, M. vaccae treatment has a beneficial effect on a person’s immune system [2].

Oddly enough, when I looked around for pictures of kids playing in dirt for this post, I found more warnings about NOT doing this due to the potential for lead poisoning. One government site features this picture with the admonition to “Cover bare dirt where children play with plants, paving stones, concrete, or bark.”

Perhaps a little common sense is useful. In our quest to meet modern standards of cleanliness, we are also reminded that a little bit of playing in the mud may not be such a bad thing. After all, our ancestors were no Martha Stewarts.

1. Lowry CA, et al., Identification of an immune-responsive mesolimbocortical serotonergic system: Potential role in regulation of emotional behavior, Neuroscience (2007), doi: 10.1016/j.neuroscience.2007.01.067
2. Rook GA et al. (2004). Mycobacteria and other environmental organisms as immunomodulators for immunoregulatory disorders. Springer Seminars in Immunopathology 25: 237-255.