Britta Gustafson: Get dirty |

Britta Gustafson: Get dirty

Studies show bacteria in soil can help mental health

Britta Gustafson
Then Again

If you want to bury your troubles, start digging.

There’s more to gardening than the promise of fresh food and fragrant flowers. Beyond connecting with nature, absorbing a little extra vitamin D from the sun and breathing fresh air, getting dirty — really getting down in the dirt — helps our mental health, too.

Here in Snowmass Village, our mountain landscape unpretentiously encourages a physically active, outdoorsy lifestyle. And for those of us who partake in any of the seemingly limitless ways to find a nature connection here, the benefits of spending time outside seem intuitive.

I have traveled across this continent enough to observe the difference in health, aging and stamina that our active community promotes. So it seems noticeably advantageous to the physical body to prioritize fresh air and fitness. But I didn’t realize how amazing digging in the dirt can actually be for our overall well-being until I began researching for myself all the benefits we can find right beneath our feet.

Soil contains, among countless other things, the bacteria Mycobacterium-vaccae, which is absorbed through the skin when gardening or even just playing in the dirt. This absorption triggers a release of serotonin, also known as the “happy hormone,” which is a natural antidepressant and mood lifter. It can even strengthen the immune system and provide a general sense of well-being. No wonder my kids come home beaming when covered in mud — and it’s not just seeing the look on my face that makes them smile.

Over the past few decades, more and more research has been devoted to highlighting Mycobacterium-vaccae and its ability to lower stress, reduce depression and improve emotional health. In fact, the benefits of soil absorption and mental health have been studied since the 1970s. But all we really need to know we learned as kids when we discovered that “a little dirt don’t hurt.”

The Proceedings of the National Academy of Sciences (PNAS) published a study in 2017 that found treatment with M. vaccae increased expression of tph2, an enzyme involved in the biosynthesis of the neurotransmitter serotonin in the brain. Previous studies also have shown that M. vaccae also increases serotonin in the prefrontal cortex, which modulates anxiety.

Immuniologist John Stanford discovered the bacterium on the shores of Lake Kyoga in Uganda, where he noticed people living in the area responded better to certain vaccines. Researchers realized that the baterium could enhance the vaccine’s efficacy thanks to its immune-modulating properties.

A University of Colorado Boulder-led study has been testing the “hygiene hypothesis,” which suggests that modern sanitary measures, antibiotic overuse and dietary changes, including easing away from healthy soils, have reduced exposure to anti-inflammatory, immune-modulating bacteria naturally present in the environment.

Lead author Christopher Lowry, who has been studying Mycobacterium vaccae’s impact on the brain over the past 20 years in the CU Department of Integrative Physiology, theorizes that a host of inflammatory diseases — including psychiatric and mental disorders — could be quelled by reintroducing “old friends” like soil.

In addition, general bacteria found in soil also provide a primary source of antibiotics and other medicines, further evidence that soil is a vital part of the human life support system.

And over time our mental health has been worsening. According to Mental Health America’s 2021 State of Mental Health in America report, 9.7% of youth in the U.S. have experienced severe major depression, compared with 9.2% in 2020. Even before COVID-19, the prevalence of mental illness among adults was increasing. In data 2017 and 2018, 19% of adults experienced mental illness, an increase of 1.5 million people over the previous year’s data.

This year, the number of people with anxiety and depression has skyrocketed. According to the same study, from January to September 2020, there was a 93% increase over the 2019 total number of anxiety screens.

With mental health becoming a significant issue across our society — perhaps in part due to an overuse of screens, a compulsion for cleanliness and an underemphasis on getting out and getting dirty — anything that helps support emotional well-being should be prioritized.

So perhaps take off the gardening gloves and dig in. After all, a little soil under your fingernails might just look better than a manicure, when it comes with a genuine smile.

I’d prescribe more time in the dirt. It really can’t hurt.

Let’s exchange a piece of my mind for a little peace of mind, after all, if we always agree, what will we talk about? Britta Gustafson appreciates an open mind; share yours and email her at

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