The Brain Benefits of Nature
Written by wellsmithhealth
According to a recent large study(1), spending time in nature is associated with a wide range of health benefits. These include lower stress hormone levels, reduced heart rate and blood pressure, and even a lower risk of diabetes. While these findings should be interpreted with caution (i.e., just because nature is associated with improved health, it doesn’t mean that nature causes improved health), they certainly suggest that nature may in fact directly promote improved health.
But how exactly might nature benefit our health?
Is it just about the exercise that often comes with being outside? Possibly, but it doesn’t seem to be that simple.
Researchers recently took a group of healthy volunteers, scanned their brains during a stressful task, and then had them take a 60-minute walk. Half the group did the walk surrounded by nature. The other half did this same walk in an urban setting.
The researchers then scanned both groups’ brains again. They found that key stress-related brain regions became less activated after the nature walk but not after the equivalent urban walk2. Basically, the nature-walkers had more “chilled out” brains.
In addition to possibly calming our brains, it seems that nature can boost our immune function.
Specifically, spending time in a forest has been shown to increase important immune cells that attack viruses and cancer. While the exact mechanisms of this are unclear, much of the immune benefits are thought to be due to “phytoncides”—natural volatile organic compounds emitted by trees that give plants that certain plant smell. Forest therapy researchers exposed human subjects to phytoncides in an urban hotel room for three nights (they did so by diffusing eucalyptus essential oil) and discovered that their virus- and cancer-attacking immune cells increased in number and activity3. Scientists are now bottling up a variety of phytoncides and studying them in mice and humans. So far, many seem to serve as natural anti-inflammatories. They have even shown promise in reducing inflammatory bowel disease in animals.
In addition to phytoncides, there are at least a couple of other “active ingredients” of nature that likely benefit our health.
Vitamin D, sunlight stimulates the release of anti-inflammatory “endorphins,” natural opioid-like compounds that help us feel good. Immersing ourselves in nature also increases our exposure to a variety of micro-organisms, potentially leading to increased microbiome diversity and improved health. Mycobacterium vaccae is one of these micro-organisms; it is an aerobic (“air breathing”) bacterium responsible for the “dirt smell” of soil. Researchers gave nebulized forms of this soil bacterium to 31 adults admitted to the hospital with moderate Covid-19. They found that M. vaccae nebulization added to standard care shortened the time interval from hospital admission to clearing the virus (determined by viral RNA measures), suggesting an immune boosting effects.
So what does immune function and inflammation have to do with brain health?
While inflammation is a necessary response to injury, it is supposed to be a time-limited process that shuts off when threat or injury is behind us. Unfortunately, when we are chronically stressed, inflammatory processes do not shut off like they are supposed to. And long-standing, chronic inflammation can be problematic for our brains. For example, high levels of inflammatory markers like interleukin 6, (“IL-6”) can interfere with our ability to make feel-good neurotransmitters like serotonin and increase compounds that can be toxic to our brain (e.g., quinolinic acid). Inflammation can be particularly problematic in aging brains, which appear to have more primed or activation-prone immune cells (microglia) that can lead to a host of bothersome brain symptoms like depression and cognitive impairment. Unsurprisingly, body-wide inflammation has recently been shown on brain imaging studies to negatively impact depression-related brain regions6. On the other hand, watching awe-inspiring videos of nature has been shown to decrease the activation of a key self-referential, rumination-related brain network implicated in a wide range of psychiatric disorders (the “default mode network”)7. This suggests that nature may serve to shift our attention away from ourselves and toward something bigger, which in and of itself may be therapeutic (much like losing oneself in a great song or a great book).
So how much time do we need to spend in nature to get some health benefits?
The “dose” is a little less clear. However, it seems that the sweet spot for stress-hormone lowering benefits occurs around the 20-30 minute mark8. Beyond that, any additional time in nature will continue to lower your stress hormone levels but will do so at a lower rate. So if you plan on spending any time in a green space, based on the limited studies we have looking at “nature dosing,” you should aim to spend at least 20 minutes doing it to gain the most stress-lowering benefits. That said, any exposure is likely better than no exposure.
1. Twohig-Bennett, C., & Jones, A. (2018). The health benefits of the great outdoors: A systematic review and meta-analysis of greenspace exposure and health outcomes. Environmental research, 166, 628–637. https://doi.org/10.1016/j.envres.2018.06.030
2. Sudimac, S., Sale, V., & Kühn, S. (2022). How nature nurtures: Amygdala activity decreases as the result of a one-hour walk in nature. Molecular psychiatry, 10.1038/s41380-022-01720-6. Advance online publication. https://doi.org/10.1038/s41380-022-01720-6
3. Li, Q., Kobayashi, M., Wakayama, Y., Inagaki, H., Katsumata, M., Hirata, Y., Hirata, K., Shimizu, T., Kawada, T., Park, B. J., Ohira, T., Kagawa, T., & Miyazaki, Y. (2009). Effect of phytoncide from trees on human natural killer cell function. International journal of immunopathology and pharmacology, 22(4), 951–959. https://doi-org.treadwell.idm.oclc.org/10.1177/039463200902200410
4. Salehi, B., Upadhyay, S., Erdogan Orhan, I., Kumar Jugran, A., L D Jayaweera, S., A Dias, D., Sharopov, F., Taheri, Y., Martins, N., Baghalpour, N., Cho, W. C., & Sharifi-Rad, J. (2019). Therapeutic Potential of α- and β-Pinene: A Miracle Gift of Nature. Biomolecules, 9(11), 738. https://doi-org.treadwell.idm.oclc.org/10.3390/biom9110738
5. Lin, Y. R., Wu, F. Y., Xiao, H., Huang, J. L., Gong, B. B., Li, Y. L., Lu, N., Jiang, X. H., Sun, Q. X., Zhang, J. F., Hu, J. T., Zhao, Y. X., & Li, C. Q. (2021). Mycobacterium vaccae Nebulization in the Treatment of COVID-19: A Randomized, Double-Blind,
Placebo-Controlled Trial. Journal of aerosol medicine and pulmonary drug delivery, 34(2), 108–114. https://doi.org/10.1089/jamp.2020.1628
6. Kitzbichler, M. G., Aruldass, A. R., Barker, G. J., Wood, T. C., Dowell, N. G., Hurley, S. A., McLean, J., Correia, M., Clarke, C., Pointon, L., Cavanagh, J., Cowen, P., Pariante, C., Cercignani, M., Neuroimmunology of Mood Disorders and Alzheimer’s Disease (NIMA) Consortium, Bullmore, E. T., & Harrison, N. A. (2021). Peripheral inflammation is associated with micro-structural and functional connectivity changes in depression-related brain networks. Molecular psychiatry, 26(12), 7346–7354. https://doi-org.treadwell.idm.oclc.org/10.1038/s41380-021-01272-1
7. van Elk, M., Arciniegas Gomez, M. A., van der Zwaag, W., van Schie, H. T., & Sauter, D. (2019). The neural correlates of the awe experience: Reduced default mode network activity during feelings of awe. Human brain mapping, 40(12), 3561–3574. https://doi.org/10.1002/hbm.24616
8. Hunter, M. R., Gillespie, B. W., & Chen, S. Y. (2019). Urban Nature Experiences Reduce Stress in the Context of Daily Life Based on Salivary Biomarkers. Frontiers in psychology, 10, 722. https://doi.org/10.3389/fpsyg.2019.00722
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