Scientists have discovered that gardening can boost your mood, especially when you are working the soil.

By Dan Nosowitz
Updated May 22, 2020
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With gardening season in full swing, you may have been planting flowers, veggies, and containers over the last few weeks. Of course, working in the yard helps relieve a little of the stir craziness we've all been feeling because of coronavirus quarantining and social distancing, but recent research has also found that digging in the dirt can boost our well-being in more ways than one. Gardening is a physical activity, something that is almost always associated with improving our mental health. The same is true for simply being outside in fresh air with plants and nature. But one of the most surprising benefits comes from the earth right beneath our feet.

Brie Passano

Soil might not look like it, but it is fantastically complex. It almost always is made up of organic material (usually from decomposing plants and animals), inorganic material like rocks or sand, tiny insects, all sorts of microbes like bacteria and fungi, and more. Research has found that a certain soil bacterium called Mycobacterium vaccae (M. vaccae) has some amazing stress-relieving abilities when we naturally breathe it in or swallow it while outdoors.

For example, a 2004 study found that cancer patients treated with this bacterium showed a noticeable improvement in mood and mental state. Follow-up studies found that mice could complete mazes faster after being fed this same microbe; the animals also showed changes in brain chemistry similar to taking an antidepressant.

More recently, scientists have discovered that M. vaccae makes an anti-inflammatory fat that could explain how it works its mood-boosting magic. Stress has been linked to causing inflammation in our bodies, which leads to a number of health problems like depression. Though that connection is not totally understood, it does seem that the anti-inflammatory substance in this bacterium has the ability to counteract our natural stress responses.

The connection between soil and mental health, or health in general, was first suggested several decades ago. In 1989, epidemiologist David Strachan combined some existing ideas about the connection into what is called the “hygiene hypothesis.” The idea is that when children grow up away from nature (in cities, for example), they aren’t exposed to enough microorganisms, and their immune systems are weaker as a result.

The recent work on M. vaccae offers a refinement of that theory. Perhaps there's more to it than just building up our immunity to disease-causing microbes. What if the life in the soil could benefit us in other ways, both physically and mentally? It would certainly give us one more good reason to get outside and play in the dirt, whether that means making mud pies with a child or doing some digging in your garden.

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