Health Benefits of Being Outside

Nature
Written By Ellie Kroeger

Most of us are familiar with the notion that being outside is beneficial for both our psychological and physiological health. What are the actual reasons it feels so good to spend time in nature?

Society is evolving faster than our genes & biology

From an evolutionary perspective, it makes sense that we crave the natural elements; our ancestors had been living outside for millions of years before modern humans bucked the trend and adopted sedentary lives in air-conditioned apartment buildings. We adapted and evolved to survive harsh conditions, endure long durations without adequate caloric intake, experience brief stress-induced cortisol spikes from our basal fluctuations, listen to natural sounds, and be in natural light cycles. Human lives today consist of minimal temperature variations, constant over-nutrition, chronic cortisol elevation, loud and disruptive industrial noise pollution, sitting in unnatural positions for hours at a time, sleep disruption and deprivation, over-sanitization, and an overall lack of tolerance for physical discomfort. These relatively-new habits of the modern human are maladaptive; our genes still expect the adversity of a hunter-gatherer lifestyle, having evolved to help us survive and prosper in times of physical stress. This juxtaposition between our genes and lifestyles may be partially to blame for the rapid rise in chronic inflammatory conditions. Unsurprisingly, naturopathic anti-inflammatory treatments revolve around living more aligned with our evolutionary adaptations. Even the best known ways to reverse aging involve techniques hunter-gatherers regularly engaged in: exercise/constant movement, caloric restriction, fasting, cold/hot exposure, and primarily plant-based diets with only quality sources of animal protein (100% pasture-raised, organic, no antibiotics).

Knowing this, it’s nearly impossible to list all of the ways in which spending more time outside benefits human health and biology. Below are a just a handful of reasons to get out in nature when possible.

  • Vitamin D

    • Although rising rates of skin cancer and proper skin protection from UV exposure should not be dismissed, adequate Vitamin D is essential and easily obtainable through small amounts of sun exposure. Sun exposure triggers the endogenous synthesis of vitamin D, which is only exogenously available through fatty fish, egg yolks, and fortified-foods (and still must be endogenously activated by hydroxylation from its biologically inert form following consumption). Given its UVB-induced endogenous synthesis from cholesterol, vitamin D is actually considered a steroid hormone. Studies have shown as little as 10-15 minutes midday may be sufficient to maintain adequate levels of vitamin D, but it is ultimately dependent on skin melanin content, time of day, cloud cover, smog, and amount of skin exposed. However, “adequate” levels may not be ideal, and even slightly-below vitamin D levels can lead to symptomatic presentations of deficiency. Alongside its well-known role in calcium absorption and bone homeostasis, vitamin D also interacts with the immune system to affect both the innate and adaptive immune systems.¹ Not only has vitamin D deficiency been implicated in COVID-19 symptom severity and complications, the supplementation of vitamin D has been shown to inhibit inflammatory cytokine production during COVID-19 infection. Vitamin D can shift the immune system from Th1 to Th2 dominance (as seen in pregnant women), inhibit inflammatory cytokine production, and increase anti-inflammatory cytokine production.¹ This evidence demonstrates vitamin D’s ability to down-regulate the over-activity of immune cells in autoimmune patients (vitamin D deficiency is commonly reported in autoimmune patients).¹ However, despite the importance of vitamin D, UV exposure must be in appropriate doses to avoid increasing the risk of skin cancer.

  • Circadian Rhythm Correction & Ideal Light Entrainment

    • Light entrainment is necessary for proper coordination of the circadian rhythm, which consists not only of our sleep-wake cycle, but also daily fluctuations in cortisol, body temperature, and feeding signaling/hormones. Without cues, the sleep-wake cycle of humans is closer to 25-26 hours; this represents the SCN electrical activity without any external inputs of light. Receiving light to retinal ganglion cells first thing in the morning can increase alertness and help regulate the circadian rhythm so one becomes tired in the evenings.² Exposure to bright light (from indoor lighting and electronics) in the evenings suppresses melatonin production and disrupts the circadian rhythm by adding an external cue that does not correspond to the natural lighting outside.³ Living outside with the natural 24-hour light cycle allows for proper circadian rhythm correction.

  • Temperature Variations & Sirtuin Activation

    • Weather conditions are highly variable, and people often only notice the weather’s immense relevance when they cannot escape it. Sunny days can be followed by cold nights; wind, rain, snow, and hail can come out of seemingly nowhere; and temperatures can fluctuate greatly over weeks, days, or even hour-to-hour. Hunter-gatherers had no asylum from these extreme conditions. Today, there has been a massive rise in the popularity of deliberate cold exposure and heat exposure due to its glucoregulatory and anti-aging effects. Cold exposure has been demonstrated to improve insulin sensitivity, decrease fasting blood glucose concentration, and increase glucose uptake.⁴ It also has been shown to stimulate brown adipose tissue (BAT), which is beneficial for thermogenesis and energy homeostasis.⁴ Cold exposure is most well-known for its role in activating sirtuins, which are NAD+-dependent deacetylases involved in DNA repair and positive epigenetic changes (histone modification and increased methylation).⁴ Heat exposure may also trigger protective mechanisms, such as the activity and concentration of heat shock proteins (which are involved in DNA repair) and the secretion of anti-inflammatory cytokines (i.e. IL-10). Novel research on NAD+ and sirtuins’ role in DNA repair and oxidative protection has led to exciting advances in longevity research and anti-aging possibilities.

  • Improved Stability & Strengthening of Small Muscles

    • Walking on uneven terrain requires greater energy expenditure than walking on even terrain.⁵ This might be due to the co-activation of smaller muscles necessary for stability.⁵ Strengthening these muscles increases balance and stability in the frontcountry as well as the backcountry, reducing the risk of falling as we age. Walking with minimalist barefoot shoes or barefoot when possible strengthens the numerous extrinsic and intrinsic muscles of the foot, as well as the underutilized neural connections between the foot and brain that are lost with constant cushioning provided by modern shoes. Although questions remain regarding the proposed vs actual benefits of barefoot shoes, anecdotal reports claim they lead to less back pain, less hip tightness, and a more natural gait.

  • Air Quality

    • Indoor levels of pollutants can be 2-5x higher than outdoor levels of pollutants, which is troubling considering how much time the average person spends indoors. Being outside also limits exposure to toxic indoor household chemicals, namely VOCs released from commonly-used cleaning products and synthetic fragrances.

  • Mental Health Improvements & Parasympathetic Nervous System Activation

    • Nature therapy is rooted in the idea that being in nature promotes healing, partially by providing psychological and physiological relaxation. The calming effect of nature has been demonstrated in a multitude of studies, mostly by revealing its ability to amplify the “rest-and-digest” parasympathetic nervous system. Studies that had subjects view natural landscapes, even electronically, experienced greater physiological changes than control groups, changes that were attributable to mental relaxation and reduced stress.⁶ Another study found that patients who had window access to view a natural setting while in the hospital had reduced durations of stay and diminished analgesic use.⁷ Other epidemiological studies note the presence of trees in a neighborhood and the decreased rates of depression.⁸ Although it still remains unclear what duration and density of “nature” is most beneficial for human health, it is safe to say that any interaction with nature is better than none.

  • Microbiome Diversity

    • Many of the microbiome benefits of being outside result indirectly from the increased parasympathetic tone and reduced stress hormones associated with being outside and/or in natural landscapes. Stress and chronic activation of the sympathetic nervous system stimulate catecholamine and cortisol synthesis and increase the production of inflammatory cytokines, negatively affecting the gut epithelial barrier, intestinal permeability, and microbial diversity. Therefore, lowering stress and decreasing sympathetic nervous system stimulation should lower inflammation and promote the integrity of the gut epithelial barrier. Similarly, lowering stress has positive benefits on the immune system, which is in constant communication with the gut. Additionally, being outside inevitably leads to an increased exposure to a wider range of microbes, which may be beneficial for increasing microbial diversity, resilience, and proper immune system regulation/strengthening. Exercise and/or some form of physical activity is usually involved in most outdoor recreation, and aerobic exercise, in any environment, has been shown to modulate the gut microbiome, as measured in microbiota-derived metabolites in the blood plasma.

  • Boredom & Creativity

    • Spending long durations of time in the backcountry often includes much-needed time away from the constant sources of intense stimulation (i.e. electronics, advertisements, noise pollution, etc.) that society inundates us with. The experience of boredom is a result of time without stimulation or productivity. Although boredom has a negative connotation in our productivity-obsessed, guilt-ridden, feeling-numbing society, recent neuroscience research indicates it may be essential for our brains to experience the cognitive rest that comes with boredom; it allows for mind-wandering and creativity.

  • Noise Pollution

    • Noise pollution infiltrates the majority of people’s lives on a daily basis. Constant exposure to industrial noises, airplanes, domestic appliances, roads & traffic can lead to sleep disturbances (which can lead to high basal levels of cortisol and dysregulated hunger signaling), higher levels of annoyance and stress, increased heart rate and sympathetic nervous system activation, and poor focus.⁹ This doesn’t include the high impact noise pollution has on animals, their communication patterns, and their daily habits.⁹ Studies comparing natural sounds to artificial sounds showed that exposure to natural sounds increased parasympathetic activity in humans, adding to the mounting evidence that nature is positively associated with stress reduction.¹⁰

  • Forest Bathing

    • Forest bathing has gained popularity as a specific form of nature therapy originating in Japan. Experiments on forest bathing show its ability to activate the parasympathetic nervous system and dampen the sympathetic nervous system.¹¹ Despite the small sample sizes of some of these studies, their results match with existing studies on other forms of nature therapy. The physiological changes that occur as a result of increased parasympathetic tone include improvements in cardiovascular function, inflammatory indexes, immune indexes, and neuroendocrine indexes.¹² Improvements in cardiovascular function might also be resulting from the physical activity often involved in forest bathing.

The reasons to spend more time in nature are endless. Of course, when spending any time in the backcountry, be sure to practice Leave No Trace principles to minimize human impact and protect the beautiful landscapes we are blessed with, the same landscapes that provide us with the health benefits above.

References

  1. Aranow C. Vitamin D and the immune system. J Investig Med [Internet]. 2011;59(6):881–6. Available from: http://dx.doi.org/10.2310/JIM.0b013e31821b8755  

  2. Figueiro MG, Nagare R, Price L. Non-visual effects of light: how to use light to promote circadian entrainment and elicit alertness. Light Res Technol [Internet]. 2018;50(1):38–62. Available from: http://dx.doi.org/10.1177/1477153517721598  

  3. Tähkämö L, Partonen T, Pesonen A-K. Systematic review of light exposure impact on human circadian rhythm. Chronobiol Int [Internet]. 2019;36(2):151–70. Available from: http://dx.doi.org/10.1080/07420528.2018.1527773  

  4. Wei X, Jia R, Yang Z, Jiang J, Huang J, Yan J, et al. NAD+ /sirtuin metabolism is enhanced in response to cold-induced changes in lipid metabolism in mouse liver: Hepatic NAD /SIRT metabolism is enhanced by cold. FEBS Lett [Internet]. 2020;594(11):1711–25. Available from: http://dx.doi.org/10.1002/1873-3468.13779  

  5. Voloshina AS, Kuo AD, Daley MA, Ferris DP. Biomechanics and energetics of walking on uneven terrain. J Exp Biol [Internet]. 2013 [cited 2023 Feb 18];216(Pt 21):3963–70. Available from: https://journals.biologists.com/jeb/article/216/21/3963/11673/Biomechanics-and-energetics-of-walking-on-uneven  

  6. Jo H, Song C, Miyazaki Y. Physiological benefits of viewing nature: A systematic review of indoor experiments. Int J Environ Res Public Health [Internet]. 2019 [cited 2023 Feb 18];16(23):4739. Available from: http://dx.doi.org/10.3390/ijerph16234739  

  7. Ulrich RS. View through a window may influence recovery from surgery. Science [Internet]. 1984;224(4647):420–1. Available from: http://dx.doi.org/10.1126/science.6143402  

  8. Taylor MS, Wheeler BW, White MP, Economou T, Osborne NJ. Research note: Urban street tree density and antidepressant prescription rates—A cross-sectional study in London, UK. Landsc Urban Plan [Internet]. 2015;136:174–9. Available from: https://www.sciencedirect.com/science/article/pii/S0169204614002941  

  9. Mohamed A-MO, Paleologos EK, Howari FM. Noise pollution and its impact on human health and the environment. In: Mohamed A-MO, Paleologos EK, Howari FM, editors. Pollution Assessment for Sustainable Practices in Applied Sciences and Engineering. Oxford, England: Elsevier; 2021. p. 975–1026.  

  10. Gould van Praag CD, Garfinkel SN, Sparasci O, Mees A, Philippides AO, Ware M, et al. Mind-wandering and alterations to default mode network connectivity when listening to naturalistic versus artificial sounds. Sci Rep [Internet]. 2017 [cited 2023 Feb 18];7(1):1–12. Available from: https://www.nature.com/articles/srep45273  

  11. Lee J, Park B-J, Tsunetsugu Y, Ohira T, Kagawa T, Miyazaki Y. Effect of forest bathing on physiological and psychological responses in young Japanese male subjects. Public Health [Internet]. 2011;125(2):93–100. Available from: https://www.sciencedirect.com/science/article/pii/S0033350610003203  

  12. Wen Y, Yan Q, Pan Y, Gu X, Liu Y. Medical empirical research on forest bathing (Shinrin-yoku): a systematic review. Environ Health Prev Med [Internet]. 2019;24(1):70. Available from: http://dx.doi.org/10.1186/s12199-019-0822-8  

Ellie Kroeger
Previous

Catecholamine Biosynthesis in the Adrenal Medulla