We have all heard that our moods (and even our thoughts) don’t live in our heads. For example, we’ve known for a while that serotonin, an important neurotransmitter that regulates mood, is found in abundance in the GI tract.1 Its role there includes managing mucus production and acid production, as well as – possibly – helping to regulate mood. Serotonin-producing cells in the GI tract, furthermore, seem to need the right signals from our gut flora (the beneficial bacteria that live in our intestines) to function properly,2 which lends additional credence to the notion that our moods are intimately connected to our internal ecologies.
But what of our external ecologies? Is there any evidence that being outside might positively impact our moods? We are, in fact, exploring this connection more and more: from “forest-bathing”, which consistently seems to reduce stress and anxiety,3 to Dr. Andrea Taylor’s work on relieving symptoms of attention deficit by walking in nature.4 Researchers have also been looking at the value of gardening as a form of therapy since the 1970s.5 The effects of working with the soil and with living, growing plants also include improvements in mood and reductions in overall stress, as reviewed by Dr. Joe Hinds and his team from Christ Church University in Kent, UK.6 About ten years ago, another team of researchers, this time led by Stafford Lightman of the University of Bristol, UK, discovered that a species of bacteria found in garden soil (Mycobacterium vaccae) was able to travel into the mucous membranes and there initiate a series of events, mediated by the immune system, that resulted in the activation of serotonin-based pathways in the GI tract.7 This in turn shifted the balance of serotonin in the central nervous system, reducing emotional distress – symptoms of anxiety and depression. Given the abundance of M. vaccae particularly in organic soil,8 it may be that part of the reason gardening is such as valuable mental health intervention is that it helps expose us to important microbial species, and allows our garden to start participating in how our neurotransmitter pathways work. Think about this – if your garden could talk, sit down with you for a cup of tea and help you with the worries and concerns of the day, would you listen? I certainly would! As it turns out, our gardens (and fields, and forests) may have been talking to us all along. This time of year, when we feel the joy of seedlings and transplants and rich, moist soil, that joy may be a manifestation of chemical and hormonal shifts that began when we chose to engage with the dirt.
Dr. Maya Shetreat-Klein, a pediatric neurologist at New York Medical College, has consistently emphasized the importance of dirt: how exposure to soil and microorganisms affects development, mood, and health.9 Her research has delved into the connection between exposure to soil and bacteria and the development of hypersensitivity diseases like asthma and allergy, but branched out from there to look at mood, behavior, and a range of other potential health benefits. This makes sense: as we saw with M. vaccae, it is often the immune system that mediates the conversation between microbes and self, and there seems to be more and more interest in the overlap between the studies of immunity, nerves, and hormones.
So might it be possible that working the garden carries more benefits than just a more balanced, focused, positive outlook to life? A recent meta-review10 has combined all of the research on gardening as an intervention to promote health and well-being. It explored over 70 research studies to compile a comprehensive overview of gardening’s benefits, and focused in on twenty-two articles that included quantitative data – meaning, just exactly how strong was the effect of gardening on things like mood, life satisfaction, heart rate variability (stress), physical activity, body mass index, and bone mineral density. Masashi Soga, working at the University of Tokyo, went through all the research in detail, excluding studies that showed signs of publication bias, and averaging out the data to provide an overall snapshot – and provided open access to the results. No studies reported negative effects from gardening, and in the end, the results are clear: working in our gardens, even if in containers on a balcony or patio, helps significantly with a range of parameters related to mood, stress, physical fitness, and the heart. This is true even in short-term interventions (just two or three hours in the soil), but becomes quite clear after folks are asked to garden daily for six or more weeks. Furthermore, it seems that the positive effects of garden therapy persist for at least three months even after the gardening stops: maybe not enough to get us through the whole winter up here in Vermont, but pretty darn close!
So this time of year, think about helping some plants grow. This can be in a container, in a community garden, or in a small section of your yard – you don’t need a prize-winning garden to reap the benefits (in fact, my personal predilection is for the weedy patches: more wild chemistry). Consider planting some medicinal plants, particularly some of the aromatic herbs like lavender and lemon balm, or the rewarding, versatile calendula whose flowers are a delight but who also helps almost everything else grow better. Even if you don’t consume any of these plants, your mood will lift, and your satisfaction with daily life will increase. I like to think that the plants, and the ecology of our balconies and back yards, are helping us share in the joy they experience as seeds burst and stems rise to the sun. May we all feel that springtime renewal of hope! As Audrey Hepburn once said, “To plant a garden is to believe in tomorrow.”
1. Ormsbee III, Herbert S., and Joseph D. Fondacaro. "Action of serotonin on the gastrointestinal tract." Proceedings of the Society for Experimental Biology and Medicine 178.3 (1985): 333-338.
2. Yano, Jessica M., et al. "Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis." Cell 161.2 (2015): 264-276.
3. Park, Bum Jin, et al. "The physiological effects of Shinrin-yoku (taking in the forest atmosphere or forest bathing): evidence from field experiments in 24 forests across Japan." Environmental health and preventive medicine 15.1 (2010): 18-26.
Taylor, Andrea Faber, Frances E. Kuo, and William C. Sullivan. "Coping with ADD: The surprising connection to green play settings." Environment and behavior 33.1 (2001): 54-77.
Kuo, Frances E., and Andrea Faber Taylor. "A potential natural treatment for attention-deficit/hyperactivity disorder: evidence from a national study." American journal of public health 94.9 (2004): 1580-1586.
Faber Taylor, Andrea, and Frances E. Ming Kuo. "Could exposure to everyday green spaces help treat ADHD? Evidence from children's play settings." Applied Psychology: Health and Well‐Being 3.3 (2011): 281-303.
Faber Taylor, Andrea, and Frances E. Kuo. "Children with attention deficits concentrate better after walk in the park." Journal of attention disorders 12.5 (2009): 402-409.
5. Sullivan, M. E. "Horticultural therapy--the role gardening plays in healing." Journal-American Health Care Association 5.3 (1979): 3-5.
6. Clatworthy, Jane, Joe Hinds, and Paul M. Camic. "Gardening as a mental health intervention: a review." Mental Health Review Journal 18.4 (2013): 214-225.
7. Lowry, Christopher A., et al. "Identification of an immune-responsive mesolimbocortical serotonergic system: potential role in regulation of emotional behavior." Neuroscience 146.2 (2007): 756-772.
8. Gcebe, Nomakorinte, et al. "Prevalence and Distribution of Non‐Tuberculous Mycobacteria (NTM) in Cattle, African Buffaloes (Syncerus caffer) and their Environments in South Africa." Transboundary and emerging diseases 60.s1 (2013): 74-84.
9. Shetreat-Klein, Maya. The Dirt Cure: Growing Healthy Kids with Food Straight from Soil. Simon and Schuster, 2016.
10. Soga, Masashi, Kevin J. Gaston, and Yuichi Yamaura. "Gardening is beneficial for health: A meta-analysis." Preventive Medicine Reports (2016).
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