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Natural Medicine Journal

February 5, 2025

Walking in Nature Changes the Brain

MRI-proven brain health effects of time spent in forested environments

Kurt Beil

ND, LAc, MPH
A one-hour nature walk physically improves the brain.

Reference

Sudimac S, Kühn S. Can a nature walk change your brain? Investigating hippocampal brain plasticity after one hour in a forest. Environ Res. 2024;262(Pt 1);119813. 

Study Objective

To determine the effect of 1 hour of walking in urban forested vs built environments on structural and functional brain regions, as measured by functional magnetic resonance imaging (fMRI)

Key Takeaway

A 1-hour walk in nature can produce measurable, positive structural changes to key brain areas involved in memory, anxiety, rumination, and the hypothalamic-pituitary-adrenal-axis (HPA) stress response.

Design

Between-subjects, randomized, controlled trial. Due to the environmental aspects of the experimental variable, blinding of participants for this type of study is not possible.

Participants

N=60 adults in Berlin, Germany, with no history of neurological or psychological disorders. The female-to-male ratio was approximately 1:1. Mean age was 27.21 years, with a standard deviation of 6.74 years. Investigators did not report any between-group differences for age, occupation, education, income, or history of urban upbringing. 

Intervention

One hour walking (~4.6 km) in a forested urban park vs built urban streetscape

Study Parameters Assessed 

Prewalk and postwalk:

Objective data included fMRI scans of brain regions of the hippocampus (regions included CA1-3, dentate gyrus, subiculum, parahippocampal gyrus, entorhinal cortex, BA 35, BA 36, and the sulcus) and the amygdala.

Subjective data included 3 items of the Stress Coping Inventory, measuring rumination (eg, “During the past 5 minutes, I could not get certain thoughts out of my head”).

Primary Outcome

Structural changes in regions of the brain related to stress response, as detected by fMRI

Key Findings

Between-group analysis demonstrated a significant pre-post size difference in the hippocampal subiculum region [F(1,58)=4.717, P=0.034, η2g=0.01], with enlargement after the forest walk [t(29)=−2.758, P=0.010] but not the urban walk [t(29)=−0.133, P=0.895]. 

Significant negative correlation between pre-post subiculum size and self-reported rumination score occurred from the forest walk [r(28)=−0.367, P=0.046] but not the urban walk [r(28)=0.102, P=0.592], with significant difference between correlation coefficients [Fisher’s z=1.79, P=0.037].

Transparency

The authors declare no competing financial or personal relationships that could have appeared to influence this study or publication.

Practice Implications & Limitations

Evidence has been growing for decades about the exposure to natural vs built environments and their impact on human health, beginning with Ulrich’s groundbreaking 1984 “A View Through a Window” study.1 Since that time, thousands of studies have demonstrated the multiple benefits that green spaces have on indicators of physical, mental, emotional, and social well-being.2–4

One of the primary pathways for this “healing power of Nature” is through modulation of the psychophysiological stress response, also first identified by Ulrich.5 By working with our inherent human affinity for nature and other living things, known as biophilia, natural settings and other stimuli tend to create more calming, restorative, salutogenic neuroendocrine responses.6–9

This “natural” tendency of natural settings to mitigate the deleterious effects of stress, known as allostatic overload,10 is limited in developed urban settings where green spaces can be scarce. Instead, the perpetual exposure to modern urban stimuli (eg, traffic, noise, pollution) can harm homeostatic regulatory systems and, through chronic exposure, contribute to the prevalence of chronic disease.11 Studies in this developing field of “urban stress” consistently show negative effects of urban living on mental health, both in the prevalence of diagnosed mental pathology12,13 and via measured alterations to brain structure and function known to correspond to mental health status.14–16

The current study explores the effect of 1-hour nature vs urban exposure on objective (hippocampal fMRI) and subjective (rumination) parameters. Past studies have demonstrated the beneficial effects of chronic nature vs urban exposures on brain activity17–19 and mental health outcomes.20,21 This is the first reported experimental study to show measurable brain changes and associated subjective experience immediately following acute exposure to natural vs built environments, suggesting structural as well as functional benefits occur from brief exposure to greenspaces. The mechanisms behind these cerebral structural changes are not known but could involve neuroplastic processes such as synaptogenesis, supporting glial processes, and dendritic branching.

This study focuses on the hippocampus, with positive results occurring in the subiculum, an area associated with spatial navigation, memory, learning, and the HPA stress response.22,23 Data from this same study published as a separate paper24 also demonstrate greenspace-related beneficial changes in the amygdala, well-known to mediate psychophysiological stress-responses such as heart-rate, cortisol, anxiety, depression, and fear.25 The fMRI data from these studies, combined with subjectively reported improvements in rumination for the nature but not urban group, add to the growing evidence in this research field.26 Rumination is a repetitive cognitive process that is a common contributing component of mental pathologies like depression, anxiety, posttraumatic stress disorder (PTSD), and obsessive-compulsive disorder (OCD),27 and research has previously shown time in nature to reduce rumination.28,29 Overall, these results suggest that a 1-hour nature vs urban walk can significantly affect healthy neurological structure and psychological function. 

The mechanisms behind these cerebral structural changes are not known but could involve neuroplastic processes such as synaptogenesis, supporting glial processes, and dendritic branching.

Regarding limitations, while the experimental pre-post design can differentiate between nature and urban settings regarding effects, it is not clear exactly what environmental aspects caused these changes. For example, it is unknown how familiar participants were with either the forest or urban setting. It is possible that novel exposure to a forest environment may have prompted hippocampal changes (ie, new environment learning). However, the expansive evidence-base for natural vs built environmental effects (see above citations) suggests that the biophilic qualities of the greenspace used in this study caused the between-group objective and subjective measured differences. 

Healthcare providers wanting to assist their patients with health concerns, including but not limited to reduction in stress, allostatic load, rumination, depression, and anxiety, may want to recommend time in nature as a low-cost adjunctive treatment for preventive and therapeutic effects. Exact dosing parameters are still being researched. One commonly referenced paper claims a minimum of 120 minutes per week of outdoor Nature Time has proven to be effective,30 while other studies suggest benefits can be achieved in just 10 minutes.31 Such “Nature Rx” prescriptions are increasingly utilized as effective methods of improving both treatment-plan adherence as well as physical and mental health.32

Categorized Under

Kurt Beil

ND, LAc, MPH

Kurt Beil, ND, LAc, MPH, is a naturopathic physician and licensed acupuncturist and holds a master’s degree in public health focused on the benefits of green space as a sustainable public-health promotion tool. He did his postdoctoral work at the Helfgott Research Institute on biomarker and psychometric assessment of the restorative and therapeutic effects of natural vs built urban environments. Dr Beil has been an advisor to the Children & Nature Network’s “Nature Research Database” and was the founding cochair of the Nature & Health subcommittee of the Intertwine Alliance in Portland. He also moderates a Facebook group NDs for Nature for the naturopathic medicine community on the clinical health benefits of contact with nature. Dr Beil maintains a clinical naturopathic and Chinese medicine practice in Happy Valley, Oregon, focusing on chronic disease. He can be reached via email or www.drkurtbeil.com.

References

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