Study: Nature walks promote mental health

reference

Bratman GN, Hamilton JP, Hahn KS, Daily GC, Gross JJ. Nature experience reduces rumination and subgenal prefrontal cortex activation.Proc Natl Acad Sci USA. 2015;112(28):8567-8572.

Design & participants

Randomized between-group comparison of a 5.3 km solo walk in either a grassland and oak natural park or a busy urban street in Palo Alto, California. Each participant received a smartphone with GPS tracking to monitor their location and take photos of their experience to ensure compliance with study instructions and hiking route.

All participants were urban residents (n = 38, 18 female, mean age 26.6 years) of the San Francisco Bay metropolitan area, with no history of neuropsychiatric illness or current use of psychotropic medications. They were randomly assigned to either the nature or urban walking group. No significant differences were found in the mean age or gender distribution of the groups.

Target parameters

Immediately before and after the walk, participants completed a psychometric and biomarker assessment of their experience.

• Psychometrisch: Der Reflection-Rumination Questionnaire (RRQ) ist eine validierte Skala zur Messung des mentalen Grübelns, das eine assoziierte Vorgeschichte von klinischen Zuständen wie Depressionen und Angstzuständen ist.¹
• Biomarker: Arterielles Spin-Labeling-MRT-Neuroimaging misst die neuronale Aktivität des subgenualen präfrontalen Kortex (sgPFC) über den zerebralen Blutfluss. Eine erhöhte sgPFC-Aktivität ist mit Erfahrungen von Traurigkeit, sozialem Rückzug und negativer Selbstreflexion verbunden, die alle mit dem Grübeln und den daraus resultierenden Bedingungen verbunden sind.²

Heart and respiratory rates were measured during neuroimaging to account for individual differences in physiological response to walking; No physiological differences were found between groups before or after the walks.

Key insights

Statistically significant differences between the nature and urban walking groups for both psychometric and biomarker analyzes showing subjective and objective changes in the psychophysiological rumination experience. The mean RRQ values ​​were significantly reduced after the nature walk [t(17)=−2.69,P<0.05, d=0.34] were unchanged after the city walk. Similarly, sgPFC blood flow was significantly decreased in the nature hike group [t(15)=−6.89,P<0.0001, d=1.01] remained unchanged for the urban walk group.

Comment & Implications

This is the first study to demonstrate neuroimaging and corresponding psychological changes in response to real-world natural vs. built environmental stresses. Other studies have reported similar fMRI results after looking at natural vs. constructed images in a laboratory.³and there is an extensive literature using animal models that demonstrate beneficial neurostructural and neurofunctional changes from living in more “natural” contexts.⁴Furthermore, the largest fMRI study on this topic shows healthier stress responses in other brain areas (e.g., pACC*, amygdala) in rural-raised adults than urban-raised adults; These results were consistent after controlling for participants' current residence.⁵Taken together, these studies demonstrate the objective changes in the functional brain that result from contact with nature.

Of course, these objective changes in the brain lead to positive thingssubjectiveExperiences of exposure to the natural environment, which have been extensively discussed in the literature.^6,7,8There is evidence that nature-based experiences are legitimate and useful complementary therapies to address mental health conditions such as depression and ADHD.^9.10Additionally, contact with nature also increases positive mental health experiences. Spending time in nature can improve a patient's lifestyle,¹¹life satisfaction,¹²and subjective well-being.¹³These aspects of “positive psychology” are increasingly being propagated in the disciplines of health promotion¹⁴and are recognized as important components for improving overall health and effectively managing and treating mental illness.¹⁵Although it is still in its infancy, environmental factors are contributingsalutogenicApproaches to mental health care are gradually being recognized.¹⁶

One facet of this positive, health-promoting quality of nature is its ability to inspire and inspire awe. Awe is a feeling of grandeur and appreciation for things greater than oneself, and as discussed in the August 2015 issue ofJournal of naturopathyit has the ability to modulate immune system function and reduce pro-inflammatory cytokines.¹⁷A recent study suggests that the awe generated by nature helps us “put things into perspective,” making us realize how small yet interconnected they are in a larger universal context.¹⁸It's possible that this relative perspective helps us overcome our own personal worries and works to break the cycle of self-doubt and rumination that leads to mental illness. The study also found that nature-inspired awe is more likely to lead to prosocial behavior, which essentially means people behave as better people toward others. This is exciting because it means that the awe inspired by nature is a truly “biopsychosocial” health promoting factor.

Regarding the limitations of the current study, it must always be noted that any “field study” contains an almost infinite number of variables that can influence the results. It is not possible to list all of the ways in which the natural and urban environments differed in this study or to isolate which of these variables are the causal factors. However, it is important to recognize that attempting to do so would defeat the purpose. Environments in which people live, work, and play are not isolated biochemical agents suitable for a randomized, placebo-controlled, double binding study. They are complex matrices of experience and commitment that constantly influence us at all levels. We are just beginning to appreciate and incorporate this awareness into our healthcare paradigm.

It is useful for the clinical practitioner to have a wide range of tools when working with patients. Getting patients outside and into a natural environment helps clear the mind, invigorate the body and restore the spirit. All in a way that works with “nature’s healing power” and doesn’t have to come in a pill.

Diploma

Supportive evidence continues to accumulate showing that spending time in nature is a valuable and beneficial activity for improving mental health, particularly among urban dwellers for whom exposure to natural environments may be limited.

*pACC = Perigenual Anterior Cyngulate Gyrus, a region of the brain in which increased activity is associated with healthy cognitive and affective processing and decreased activity is associated with mental-emotional pathology.¹⁹