Researchers have found that a lowly bacteria named Mycobacterium vaccae, commonly found in dirt, may have natural antidepressant effects through boosting serotonin levels. Avid gardeners already know that working in dirt is a mood lifter and stress reducer. Scientists became interested after human cancer patients who were treated with M. vaccae unexpectedly reported improvements in their quality of life. The original study, from the University of Bristol and University College London, was published in a 2007 issue of Neuroscience.
Lead study author Dr. Chris Lowry and colleagues reasoned that the bacteria were stimulating neurons in the brain to produce more serotonin. It is thought that depression is caused by a lack of serotonin in the brain, which is also linked with other disorders such as anxiety, aggression, bipolar disorder, obsessive compulsive disorder, irritable bowel and fibromyalgia.
Serotonin is found in the brain, nerves, gut and blood of animals and humans. It sends messages between cells in the brain and central nervous system, constricts blood vessels, regulates the secretion of digestive juices and helps control the passage of food through the gut. Different parts of body and brain need different levels of serotonin. The brain balances these levels in three ways: through releasing it, inactivating it after it is released and by absorbing it, known as reuptake.
The study used mice, whose brains showed that treatment with M. vaccae activated a group of neurons that produces serotonin. Current antidepressant medications work in one of two ways. Monoamine oxidase (MAO) inhibitors work by reducing the brain’s ability to inactivate serotonin. Selective serotonin reuptake inhibitors (SSRIs) slow the process of serotonin reuptake in the brain. Increasing the release of serotonin, such as was found with M. vaccae, would be a third way of causing an antidepressant effect.
During the research mice were injected with M. vaccae and then put through exercises where they had to perform behavioral tasks that are commonly used to test the efficacy of antidepressant drugs. for example, when placed in a large beaker of water, the bacteria-exposed mice paddled around looking for an exit for much longer than the control group of mice.
More recently researchers at Sage Colleges in Troy, NY tested the antidepressant dirt theory by running mice through a difficult maze. The mice that were fed the M. vaccae bacteria ran the maze twice as fast and showed only half of the anxiety behaviors as the control group. It is thought that seratonin also plays a role in learning, so the mice may have done better not only because they were less anxious but because they had greater concentration. The effects continued for about three weeks after the bacterium was removed from their diets.
The study opens questions about why depression is becoming more common, and theories include the idea that the hygienic modern environment perhaps does not allow children to be exposed to the harmless bugs that can help develop their immune systems. It also opens questions as to the possibility of some day treating clinical depression with a vaccine.
Lowry said the studies help with understanding how the brain and body communicate and why a healthy immune system is important for maintaining mental health. “They also leave us wondering if we shouldn’t all be spending more time playing in the dirt.”
Gardeners turn up dirt, releasing the friendly bacteria which is then inhaled, or get it into the bloodstream through contact with the skin. Future studies are needed to determine whether the friendly M. vaccae bacteria found in dirt really does have antidepressant properties through the stimulation of serotonin neurons. M. vaccae can be purchased in pill form, but dirt treatment may be more fun.
By Beth A. Balen