By Tamara Claire Fernandez
With the temporary closure of public gyms and sports facilities, millions have turned to parks and nature trails to keep active instead. Apart from the physical benefits of exercising in these natural areas, there are more subtle advantages of nature exposure that are often overlooked. From reducing anxiety to boosting immune health, Mother Earth presents myriad direct and indirect boons to our overall health and vitality (Williams, 2017). Origins of nature immersion therapy can be traced back to the Persian empire in 2500 BC, but its practices have been re-popularised in the 1980s through Shinrin-Yoku (forest bathing) in Japan (Hansen et al., 2017). Now, medical practitioners in California, Finland and South Korea are starting to prescribe nature to patients instead of modern pharmaceuticals (Williams, 2017). This rising trend of nature immersion therapy being incorporated into modern healthcare programmes points to strong evidence supporting their success, begging the question as to why and how nature is such a powerful tool in combating mental and physical illness.
Notably, the effects of nature therapy begin from a tender age. For instance, reduced exposure to natural light was found to be associated with a significant increase in children’s myopic spherical equivalent refraction (SER) (p = 0.009), promoting the development of myopia particularly between the ages of 6 to 9.4 years old (Sánchez-Tocino et al., 2019). Coupled with the team’s finding that SER has a significantly higher increase in months with fewer daylight hours (p < 0.001), this strongly suggests a correlation between daylight exposure and myopia progression. As it turns out, an alleviant of the world’s leading cause of distance visual impairment could be simply bathing in natural light (Holden et al., 2016). Another common condition that surfaces in childhood is Attention Deficit Hyperactivity Disorder (ADHD). In a study by Taylor & Kuo (2009), children aged between 7 and 12 years old with ADHD were brought out for 20-minute walks to one of three random locations: an urban park, a residential area or a downtown area. Overall, the children performed better in post-walk concentration tasks after walking in the park, as compared to both the downtown (p = 0.0229) and neighbourhood (p = 0.0072) walks. This is congruent with Kaplan’s (1995) Attention Restorative Theory (ART), which proposes that nature relaxes the mind by allowing for an involuntary, soft focus on nature sights, sounds and smells. Indeed, it seems that high-level cognitive functions mediated by the prefrontal cortex, such as focusing on a specific task, solving problems and controlling impulses, are improved after rejuvenation in a natural environment (Atchley et al., 2012). Compared to controversial ADHD drugs like Ritalin which present numerous potential adverse effects (Khalili et al., 2014), nature offers a safe and practically free therapy option for ADHD.
Moving on to adolescence and young adulthood, being plagued by self-esteem issues is not uncommon. While there is no immediate cure for them, nature could help to improve one’s overall esteem and mood (Barton & Pretty, 2010). In healthy individuals, a short 90-minute nature walk reduced neural activity in the subgenual prefrontal cortex (sgPFC), measured by lower regional cerebral blood flow to the area (Bratman et al., 2015). The sgPFC is a brain region associated with behavioural withdrawal due to self-focused rumination, thus a quieter sgPFC is desirable for self-esteem and sociability. In contrast, 90-minute urban walks did not yield the same result despite having similar effects on heart and respiration rates, suggesting that a variance in physiological effects was not associated with this improvement in self-esteem. Green environments, with their panoramic views and lack of distracting noises, appear to encourage people to look outward instead of inward (Herzog et al., 2003). This could be a viable strategy in impeding the development of depression and other psychological illnesses.
Furthermore, chemicals released by plants could play a part in boosting immunity. This could be especially useful in fighting infection and promoting recovery among vulnerable groups like the young, elderly and sick. To illustrate, among Japanese adults who took a 3-day/2-night forest trip, mean Natural Killer (NK) cell activity levels as well as the number of NK cells, granulysin-, perforin-, and granzyme-expressing cells were higher during the trip than otherwise (Li, 2009). Such results have been attributed to the inhalation of volatile, antimicrobial wood essential oils called phytoncides. Examples include α-pinene and limonene, some of which possess anti-tumour properties due to their immunomodulatory effects (da Silva et al, 2007). The increased NK activity among forest bathers lasted for 30 days (Li, 2009), suggesting a prolonged positive influence of nature exposure on immunity.
However, given that 33% of the world is projected to live in urban areas by 2050, access to natural areas is becoming increasingly limited (United Nations, 2014). Fortunately, technology has enabled us to emulate nature immersion indoors. For instance, MRI scanner-based studies have found that listening to nature sounds can have a similar comforting effect by shifting from sympathetic to parasympathetic nervous system activation, reversing the neurological effects of stress (Gould van Praag et al., 2017). Likewise, α-pinene and β-pinene emitted by humidifiers with Chamaecyparis obtusa (hinoki cypress) stem oil in hotel rooms boosted NK cell activity in guests over three days (Li et al, 2009). Interestingly, when naturalising one’s living or learning space, incorporating living plants offers greater psychological relaxation than photographed or artificial plants. This discrepancy is likely due to the beneficial effects of living plants on senses apart from sight, such as smell (Oh et al., 2019).
In summary, that short walk through a park is more important than it seems. Just a weekly two-hour nature walk could present an inexpensive, yet effective, form of therapy to lift one’s spirits, especially in these tumultuous times (White et al., 2019). To ensure that more people are able to reap these benefits, it is important that access to nature areas be taken into account when it comes to urban development. Nature immersion is not a silver bullet and cannot treat all forms of illnesses, but it does offer an easy first step towards healing.
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Imperial Bioscience Review 