The Curious Case of the Antidepressant, Anti-Anxiety Backyard Garden
Image: Daphne Miller collecting late-season parsley tomatoes and pineapple guavas for her backyard compost in Berkeley California.
Originally posted on YES! Magazine by DAPHNE MILLER
Whether it's microbes in the dirt or fresh air—or both—researchers do know this: Gardening is strong medicine.
Gardening is my Prozac. The time I dedicate to training tomato vines or hacking at berry bushes seems to help me stave off feelings of sadness or dread and calm the chatter in my mind. My vegetable beds have even buoyed me through more acute stressors, such as my medical internship, my daughter’s departure for college, and a loved one’s cancer treatment. I’m not alone in appreciating the antidepressant and anti-anxiety effects of gardening—countless blogs are dedicated to this very subject, and a rash of new studies has documented that spending time around greenery can lead to improved mental health.
The idea that microbes in our environment might impact our health was not new to me. It’s well-established that the microbes in soil enhance the nutritional value of food and, as found in studies of farm children in Bavaria and among the Indiana Amish, improve immune function. (Researchers were finding that exposure to a diversity of microbes early in life led to fewer allergies.) But garden microbes acting as mood enhancers—well, this was news to me.“How does this work?” I asked Jill Litt several years ago when I first became interested in what I call gardening’s “bio-euphoric” effect and was wondering whether to prescribe this activity to my depressed patients. Litt, a professor at the University of Colorado School of Public Health, was studying gardening’s impact on a variety of health outcomes—including mood disorders. She rattled off a list of possible explanations, including that gardens create community, encourage physical activity, offer a bounty of nutrient-rich food, and expose one to Vitamin D-producing sunshine, which helps regulate serotonin, the “happiness” neurotransmitter. But then Litt surprised me by adding, “Also there are the microbes themselves. We have no idea what they are doing.”
I soon discovered that there is, in fact, evidence to back up this idea. It’s a smattering of data, and most of it has been collected on our distant cousins, the mice, but it is still compelling.
This investigation into the soil-mood connection began, like much of science, quite serendipitously. British researchers were testing whether immune stimulation with Mycobacterium vaccae, a harmless microbe found in soil and water and potentially on unwashed vegetables, might help treat lung cancer in humans. While they discovered unchanged life expectancy in the subjects treated with the M. vaccae, they were surprised that these patients scored much higher on a standard quality-of-life questionnaire than the controls. Somehow the bug had enhanced their mood.
This finding inspired another researcher, Chris Lowry, a behavioral endocrinologist at the University of Colorado Boulder, to inject heat-killed M. vaccae into the bronchi of mice. The rodents, like the cancer patients, seemed to derive a psychological benefit from the treatment, exhibiting less depression and anxiety on a stressful “forced swim test.” In their article in Neuroscience, Lowry and his colleagues hypothesize that the immune reaction to M. vaccae activates the release of brain serotonin leading to reduced stress-related behavior.
Building on Lowry’s work, Susan Jenks and Dorothy Matthews, two researchers at Sage Colleges in Troy, New York, decided to administer M. vaccae to their mice and perform a new set of behavioral tests. Instead of using the heat-killed M. vaccae used in previous experiments, they cultured the live organism and fed it to the mice via a concoction of Wonderbread and peanut butter. It occurred to me that this exposure method most closely mirrored how I might come in contact with M. vaccae: by eating the casually washed greens that I regularly harvest from my backyard.