Granted, we’ve long known that locally grown fruit and vegetables taste better and save much of the energy conventionally used in growing, processing, transporting, distributing and marketing produce. And increasingly we recognize the benefits of the gentle exercise involved in gardening and its therapeutic effect of connecting us to nature and life on a fundamental level.

Until recently, though, we have almost ignored the potentially powerful side effect of getting our hands into the dirt or even eating a little dirt that may still cling to locally grown fruits and vegetables.

Though not widely publicized, it has been known for a while that a humble strain of bacteria found in dirt may be able to boost our immune systems to resist some of the most pernicious diseases, elevate our mood and boost the brain’s ability to absorb new information.

 The name of the bacteria capable of these good deeds is M.vaccae (short for Mycobacterium vaccae) and it is found naturally in soil. M.vaccae is a harmless relative of the harmful bug that causes tuberculosis and leprosy.  It takes its name from vacca, the Latin word for cow, as it was first cultured from cow dung in Austria. 

We now think that kids making mud pies and gardeners digging in the dirt without gloves absorb these bacteria through small skin abrasions or that they breathe them in.

The discovery of the bacteria’s potential benefits began as the result of an experiment by Mary O’Brien, a consultant medical oncologist specializing in breast and lung cancer at the Royal Marsden Hospital in London. Dr. O’Brien was trying an experimental treatment for lung cancer which consisted of inoculating patients with killed  M.vaccae. Dr. O’Brien observed that inoculated patients not only had fewer cancer symptoms, but also showed improvement in their emotional health, vitality and general cognitive function.

Based on these observations, Dr. Chris Lowry, a neuroscientist at Bristol University, hypothesized that the immune response to M.vaccae induces the brain to produce serotonin, a drug that reduces stress and prevents depression. To test his hypothesis Lowry injected mice with M. vaccae and through a series of experiments was able to show that M.vaccae lowered stress, increased activity, vitality and concentration - at least in the mice.  

 More recent research conducted by Dorothy Matthews and Susan Jenks of the Sage Colleges in Troy, N.Y.  seems to confirm some of Chris Lowry’s findings.  Mice injected with M.vaccae showed some growth of neurons, as well as higher serotonin levels and lower levels of anxiety.

These results are intriguing because they open the possibility of treating cancer and clinical depression with a vaccination of  M.vaccae. They also suggest the possibility of the bug being used to treat Crohn’s disease and rheumatoid arthritis as well as depression and cancer. Don’t get carried away just yet, though. The research is pretty thin.  

But results so far do open the door to a new line of inquiry as to why depression, asthma and allergies (both caused by the immune system attacking body cells it is supposed to be protecting) are on the rise. One explanation is the hygiene hypothesis. It suggests that sharply reduced childhood exposure to harmless bugs is leading to improperly primed immune systems which then go on to look for trouble where none exists.

Lots of questions, some with answers yet to come. But, as Chris Lowry puts it, “They also leave us wondering if we shouldn’t be spending more time playing in the dirt.”