Get down and dirty

If puttering in the garden makes you happy, there’s a reason.

No poetry or philosophy here. You won’t be reading about manual labor easing troublesome thoughts.

It’s the dirt. Dirt makes you happy.

Back in 2007, researchers from Bristol University and University College London discovered that “friendly” bacteria in soil stimulates brain cells to produce serotonin, similar to the way antidepressant drugs work. Serotonin is a neurotransmitter that sends messages between cells in the brain and within the central nervous system, constricts blood vessels, regulates secretion of digestive juices and helps control the passage of food through the gut. In the brain, serotonin is used by the hypothalamus (mood regulation) and cortex (complex processes such as thinking, memory, attention and awareness).

Healthy or sick, we could all use some good dirt.

The researchers became intrigued by the dirt-brain link after learning that cancer patients treated with Mycobacterium vaccae — commonly found in soil — reported increased quality of life. The researchers speculated the bacteria may have activated brain cells to release more serotonin, so they set out to prove it with mice, whose brains work similarly to ours. They were right.

As lead researcher Dr. Chris Lowry told Medical News Today, the results “leave us wondering if we shouldn’t all be spending more time playing in the dirt.”

The study, published in the March 2007 journal Neuroscience, suggested the research may explain why serotonin imbalances in the immune system make some people more vulnerable to mood disorders such as depression. Later, in a 2017 University of Colorado-Boulder study, Lowry found the same bacterium reduced anxiety in mice facing stressful situations. He launched a clinical trial using it to treat veterans with PTSD.

What does all this have to do with gardening? A Korean study made the link. Research published in the April 2022 American Society for Horticulture journal examined healthy adult responses to, as Dr. Lowry suggested in 2007, “playing in the dirt.” After just five minutes of working with soil and incidentally breathing in traces of the same bacterium, M. vaccae, participants showed improved psychological and physical health. More specifically, blood samples, ECGs and other tests immediately before and after working with soil showed increased serotonin, reduced heart rate and several other indicators of improved physical and mental condition.

While we don’t know how long that dirt-kick lasts (no measure was taken later), gardening enthusiasts know their hobby is a quality-of-life enhancer. Previous studies indicated that simply staring at green plants stabilizes the human autonomic nervous system and activates the alpha frequency of brain waves, leading to physiological and psychological relaxation (Ikei et al., 2014; Park et al., 2016). Even simply being near plants for prolonged periods can reduce sympathetic nerve activity, resulting in relaxation (Park et al., 2017).

More plants indoors and out. A good thing.

As the years go by, people increasingly live and work in stressed, urban settings with less exposure to nature. At the very least, making a regular effort to putter in the soil, even just potted plants, could be a low-cost, no-risk health and happy boost.

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Sholeh Patrick is a columnist for the Hagadone News Network and nature lover with a black thumb. Email sholeh@cdapress.com.