"In the Spring, at the end of the day, you should smell like dirt"
Spring has sprung, time to plunge your hands into the soil. For your health.
We have just passed the Vernal Equinox and that welcome sunshine pours in my windows. I eagerly grasp my shovel and trowel and tackle the earth. Time to make ready for those garden goodies to come. And in so doing, soak up all those benefits from the soil itself.
Epidemiological evidence links natural green space exposure with better health. Conversely, greater urbanization directly correlates with an increased risk of disordered mood and mentation. Research into revegetated and remnant woodlands showed that they contained more native plant species than of the other green spaces - e.g. lawns and vacant lots - and had greater diversity of microbiota, similar to those found in natural woodlands. But, those broad green lawns and weedy vacant lots, had less microbiota diversity.
A link to microbiomes may help explain many green space-human health associations. Controlled experimental evidence testing possible beneficial effects from passive exposure to natural biodiversity via airborne microbiota demonstrate that realistic exposures to dust from a high biodiversity soil can change mouse gut microbiota. A soil-derived anaerobic spore-forming butyrate-producer, Kineothrix alysoides, increased in the gut microbiomes of high biodiversity treatment mice, and correlated with reduced anxiety-like behavior in mice. Biodiverse soils may represent an important source of butyrate-producing bacteria capable of reseeding the mammalian gut microbiome, potentially improving gut and mental health.
Another study investigated Mycobacterium vaccae, an environmental bacterium that feeds on decaying organic matter. Researchers purified and identified a unique anti-inflammatory triglyceride derived from the soil bacterium. They then synthesized and tested the free fatty acid version [10(Z)-hexadecenoic acid] in mouse macrophages. The fatty acid bound to the peroxisome proliferator activated receptor (PPAR) in the cells, which then blocked a number of inflammation-driving molecular pathways. Pretreating cells with the fatty acid before stimulating them increased their resistance to inflammation. In particular, effects of 10(Z)-hexadecenoic acid on lipopolysaccharide-stimulated secretion of IL-6 were prevented by PPARα antagonists and were absent in PPARα-deficient mice.
Indeed, generally spending time outdoors, taking time to surround yourself with greenery and living things can be one of life's great joys—and it's not just good for your body, also for your brain. Just two hours a week in nature is enough to demonstrate better health and well-being. A recent study of psychiatric inpatients who participated in a hospital based community garden showed:
Gardening stimulated reflective process whereby participants used the garden symbolically to gain insight into their illness
Exposure to nature and sensory stimulation provided calmness and a change of environment from the sterile hospital unit
Often resulted in descriptions of improved mood and pro-social behavior
Fostered a sense of community, belonging, shared purpose, and reduced isolation
Offered temporary distraction from unpleasant thoughts
But benefits extend to tending plants indoors, as well. In a recent study of 24 young male adults, using crossover experimental design, compared the differences in physiological responses to a computer task and a plant-related task. The first group carried out transplanting of an indoor plant, whereas the second group worked on a computer task. Then, each subject switched activities. The psychological evaluation used the semantic differential method (SDM) and the physiological evaluation measured heart rate variability along with blood pressure. Analysis of the SDM data showed that the feelings during the transplanting task were different from that during the computer task: the subjects felt more comfortable, soothed, and natural after the transplanting task than after the computer task. The sympathetic activity increased over time during the computer task but significantly decreased at the end of the transplanting task. Diastolic blood pressure was significantly lower after the transplanting task.
Active interaction with indoor plants can reduce physiological and psychological stress compared with mental computer work, by suppressing sympathetic nervous system activity, and promoting soothing / calm feelings.
And remember Dear Readers, to connect with Earth’s grounding energies while rolling around in that dirt. Barefoot is best. Clothing optional …
[see newsletter, “Vagaries of the Vagus”]
REFERENCES
JG. Mills et al. Revegetation of urban green space rewilds soil
microbiotas with implications for human health and urban design, Restoration Ecology (2020). DOI:10.1111/rec.13175
C Liddicoat et al. Naturally-diverse airborne environmental microbial exposures modulate the gut microbiome and may provide anxiolytic benefits in mice. Science of The Total Environment Volume 701, 20 January 2020, 134684 https://doi.org/10.1016/j.scitotenv.2019.134684
DG Smith et al. Identification and characterization of a novel anti-inflammatory lipid isolated from Mycobacterium vaccae, a soil-derived bacterium with immunoregulatory and stress resilience properties. Psychopharmacology volume 236, pages 1653–1670 (2019)
Anxiety and depression: Why doctors are prescribing gardening rather than drugs (2019, September 2) https://medicalxpress.com/news/2019-09-anxiety-depression-doctors-gardening-drugs.html
Huibrie C. Pieters et al. Gardening on a psychiatric inpatient unit: Cultivating recovery, Archives of Psychiatric Nursing (2018). DOI: 10.1016/j.apnu.2018.10.001
Min-sun Lee et al. Interaction with indoor plants may reduce psychological and physiological stress by suppressing autonomic nervous system activity in young adults: a randomized crossover study J Physiol Anthropol. 2015; 34(1): 21. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4419447/
Indoor green wall affects health-associated commensal skin microbiota and enhances immune regulation: a randomized trial among urban office workers https://www.nature.com/articles/s41598-022-10432-4