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.