How Dirt Acts as an Anti-Depressant

Perhaps you’ve had a diagnosis and prescription from a doctor that you thought a bit odd. But if you go in complaining of depression and the doc tells you to take up gardening, hear him out. Research has shown a direct correlation between Mycobacterium vaccae (a bacterium found in soil) and the serotonin levels in the brain.

 Studies of Mycobacterium vaccae

In a 2007 study, Dr. Christopher Lowry and colleagues at the University of Bristol, England, injected mice with a specially prepared solution of M. vaccae. In the control group, “they found that serotonin-producing neurons in…the dorsal raphe nucleus (region of the brain)…were more active in the treated mice….They also found increases in serotonin itself in the prefrontal cortex.” In a study with a second group of mice, Lowry stated that the bacteria “had the exact same effect as antidepressant drugs.”

But that is not all. Researchers continue to study the effects that this species of the Mycobacteriaceae family of bacteria might have on allergic asthma, cancer, depression, tuberculosis and various skin conditions—including leprosy. Naturally occurring in the soil, this bacterium is also the basis for a vaccine used to treat tuberculosis.

 How Serotonin Works

How does this work? Serotonin is a neurotransmitter found in the gastro-intestinal tract, platelets, and central nervous system of humans. About 90% of a person’s serotonin is found in the gut and regulates intestinal movement. The remainder is used by the CNS to regulate mood, appetite, and sleep. It also plays an important role in memory and learning. According to scientists from the Georgetown University Medical Center and a Canadian research institute, “serotonin is passed between key cells in the immune system, and that the chemical is specifically used to activate an immune response.” So, if exposure to M. vaccae through the soil increases serotonin levels in the brain, it stands to reason that the body’s immune system is boosted as well. And, if our body’s immune system is strengthened, than its ability to fight or ward off these other illnesses is strengthened.

So, does gardening, working in the yard, or merely taking a walk relieve the symptoms of depression or some of these other ailments? Lowry’s study shows that simply inhaling or ingesting M. vaccae can boost one’s mood. This finding suggests that simply mowing the lawn or walking a dusty road could expose one to a dose of this mood boosting bacteria. However unlike pharmaceuticals, a person cannot overdose on too much of the great outdoors.

 Other Natural Ways to Fight Depression

Simon N. Young, Editor-in-chief, Journal of Psychiatry and Neuroscience, and Department of Psychiatry, McGill University, Montréal, Quebec, reports in “How to Increase Serotonin in the Human Brain without Drugs” that exposure to sunlight and exercise can both help to elevate the mood in depressed individuals. In this article, Young states that in addition to the decrease in human exposure to bright light, “there has been a large change in the level of vigorous physical exercise experienced since humans were…engaged primarily in agriculture…and that the decline in vigorous physical exercise…may contribute to the high level of depression in today’s society.”

In light of these findings, if you couple the effects of M. vaccae on a person’s serotonin levels with that of the sun and exercise, gardening would be the activity of choice for those suffering from depression.





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