The Health Benefits from Exposure to Green Spaces and Natural Environments by Jenny Henderson, ND & Elizabeth Goldspink, ND
Abstract
Exposure to green spaces and natural environments is associated with a wide range of benefits to humans that touch on every major physiological system. A rapidly growing body of research has demonstrated improvements in cardiovascular health, immune function, stress response, inflammation, mental health outcomes, sleep quality, and cognitive function. Key research from the last 20 years is summarized here, with a discussion on possible mechanisms of action. While more rigorous research in the field is still needed, we expect the overwhelmingly positive associations that have been found thus far to be sufficient to confidently recommend regular exposure to natural environments to all urban dwellers.
Introduction
As a growing global population increasingly inhabits urban centers, humans find themselves living apart from natural spaces, both in distance and in lifestyle. Researchers have been turning their attention toward investigating nature’s role in human health for several decades, with a marked acceleration in the past 15 years. Logan and Selhub released their book “Your Brain on Nature” in 2012 where they assembled scientific evidence around the psychological, social, and physical health benefits of nature, and advise physicians to recommend “Vitamin G”, aka green space, to patients. Prior to that, it was author and researcher Richard Louv who garnered popular interest in this topic in 2005 and coined the name “Nature Deficit Disorder” to highlight the growing gap between people and nature. He postulates a theory called “The Nature Principle” and states that reconnection with the natural world is fundamental to human health and wellbeing (Louv 2005). These ideas of course are not novel. Most of us intuitively understand that connection to nature is linked with wellbeing, and literature and policy concerning this has been around for centuries (Hansen et al 2017). The Japanese in particular have understood this relationship well and their researchers have long been looking at the health effects of spending time in nature, or what they call “forest bathing” (Logan and Selhub 2012). More recently, these theories have been gaining a lot of support through a growing body of scientific evidence showing that the healing power of nature has measurable physical, psychological, and emotional effects. In many ways, the research is still new in the sense that there is still much heterogeneity, small sample sizes, and a lack of standardization. Nonetheless, there is now so much of it, that the collective results confidently support the conclusion that there is benefit to be derived from spending time in nature and increasing green spaces in cities. A 2018 systematic review and meta-analysis collected data on greenspace exposure and health outcomes, and the results show a wide range of beneficial effects; reduced cortisol levels, improved cardiovascular parameters (heart rate, blood pressure, heart rate variability, cholesterol), improvements in type II diabetes, reduced mortality (all-cause and cardiovascular), and better pregnancy outcomes (Twohig-Bennett and Jones 2018). Another systematic review on forest bathing compiled studies that collectively show significant improvements in parameters relating to almost every body system, namely cardiovascular, hemodynamic, neuroendocrine, metabolic, immunity and inflammatory, antioxidant, electrophysiological, as well as improved emotional state and attitude, physical and psychological recovery, adaptive behaviors, anxiety and depression (Wen et al 2019).
Effects of Green Exercise
Physical activity is firmly established as a critical component of good health (Twohig-Bennett and Jones 2018). A systematic review published in 2011 concluded that there are additional benefits to mental and physical wellbeing resulting from exercising in nature (Coon et al 2011). The research team analyzed data from 11 randomized and non-randomized control trials comprising 833 adults. Eligible trials were those that compared the effects of outdoor exercise with indoor exercise and that reported physical or mental well-being outcomes. The review found improvement in mental wellbeing: increased energy and feelings of revitalization, and decreased tension, anger and depression compared with exercising indoors. Participants also reported greater enjoyment and satisfaction with outdoor activities (Coon et al 2011).
A 2010 meta-analysis by Barton and colleagues showed dose responses for duration of exposure to nature and intensity of exercise on the psychological parameters of mood and self-esteem. The greatest changes came from as few as five minutes of activity, thus suggesting that psychological parameters are immediately improved by green exercise. The benefits were lower for 10-60min of exposure, but rise again for whole-day duration. For intensity the greatest benefits are derived from either light activity or vigorous activity, but interestingly drop for moderate activity (Barton and Pretty 2010).
These studies, and many others, have collectively shown that green exercise can reduce stress, depression and blood pressure, increase self-esteem, mood and wellbeing, and enhance heart rate variability, in adults as well as children (Rogerson 2020 et al). These improvements can be felt after an acute bout of green exercise, or maintained over the long term, with regular doses of green exercise (Rogerson et al 2020).
Nature Exposure Reduces Cortisol Levels and the Stress Response
Chronically elevated cortisol levels are frequently seen in clinical practice. Stressful jobs, inadequate work-life balance, socioeconomic stressors, lack of sleep, and inadequate exercise are often the culprits. Cortisol is an important biological mediator of illness, and can play an important role in the progression of many diseases. A study by Vogelzangs and colleagues (2010) showed that high levels of cortisol measured in urine were associated with a dramatic increase in death from cardiovascular disease. Study participants with the highest levels were five times more likely to die from a heart attack or stroke than those with the lowest level. Since heart disease is the most common cause of death in North America, interventions that decrease risk are essential.
Several studies have looked at how salivary cortisol levels are affected by spending time in nature. The vast majority conclude that exposure to green spaces lowers salivary cortisol levels compared to pre-exposure baselines and controls, which is associated with reduced stress (Antonelli et al 2019, Hansen et al 2017, Li 2019, Twohig-Bennett and Jones 2018, Wen et al 2019).
A small but compelling Japanese cross-over study by Park and colleagues in 2007 demonstrated this effect. The researchers measured differences in salivary cortisol and prefrontal lobe activity between participants who spent a day in a forested area and those who spend the day in an urban area. When exposed to the natural setting, the participants not only had up to 50% lower levels of salivary cortisol compared to urban exposure, but also had significantly lower activation of the prefrontal cortex, which corresponds to their increased subjective ratings of comfort and calmness. Essentially, participants were feeling a lot less stressed and on “high-alert” when they were spending time in a natural setting. This can also be measured by assessing heart rate variability (HRV), with high frequency (HF) variability considered to be associated with parasympathetic nervous system activation and therefore lowered stress levels. Forest bathing has been shown to increase HF HRV (Hansen et al 2017).
A stress and cortisol reducing effect from green spaces can be achieved within cities as well. A study by Roe and colleagues (2013) found that exposure to natural green spaces within urban neighbourhoods resulted in healthier diurnal cortisol responses in middle-aged men and women from deprived urban environments, as well as reducing their perception of stress. This suggests that the dose of nature need not be massive to achieve the desired stress-reducing effect. Moreover, even gardening can have measurable stress reducing, and quality-of-life improving effects (Soga and Gaston 2016a, Van Den Berg and Custers 2011).
Nature Improves Cardiovascular Parameters and Reduces Risk
Cardiovascular disease and its risk factors are all too prevalent in primary care, therefore it is important to have a wide arsenal of recommendations. The research into cardiovascular benefits is somewhat more robust than for other body systems. Exposure to natural environments is associated with decreased heart rate, blood pressure, cholesterol, low frequency heart rate variability, stroke risk, CVD risk, and even cardiovascular mortality (Bhatnagar 2017, Gascon et al 2016, Li 2019, Tsunetsugu et al 2013, Twohig-Bennet and Jones 2018, Wen et al 2019, Yeager et al 2020).
Hypertension especially appears to be most susceptible to amelioration by nature exposure. The explanation as to why spending time in nature has such a reproducible effect on blood pressure is multi-factorial. It appears that there is an increase in parasympathetic nervous system activation, and a decrease in sympathetic activation, a decrease in cortisol levels, and an increase in subjective relaxation; all blood pressure reducing factors (Hansen et al 2017, Tsunetsugu et al 2013).
As an example, a research team out of China (Mao et al 2012) conducted a study to investigate the effect of natural spaces on cardiovascular biomarkers. Twenty-four comparable elderly participants with essential hypertension were divided into two groups, one group spent a day walking in the city, and the other in a national forest in similar, controlled manners. The team measured blood pressure, heart rate, and pulse pressure, as well as running assays to track any changes in interleukin-6 (IL6), tumor necrosis factor alpha (TNF-a), endothelin-1, homocysteine, renin, angiotensinogen (AGT), angiotensin II, angiotensin II type 1 receptor (AT1), and angiotensin II type 2 receptor (AT2). There were some significant differences between the two groups. Compared to the city group, those who walked in the forest had significantly lower blood pressure. Endothelin-1, homocysteine, AGT, AT1, and AT2 were also significantly lower in the forest group (Mao et al 2012). These serum factors are closely associated with essential hypertension. It is yet unclear if these kinds of effects are short-lived and limited to the time spent in nature or whether the changes endure. At the very least, it is very clear that a natural setting offers a respite for the cardiovascular system.
Nature Boosts Immune Activity
Stress hormones can compromise immune function by suppressing the action of natural killer (NK) cells (Li et al 2009). Evidence out of Asia is demonstrating that nature exposure increases NK cell activity (Li 2019, Wen et al 2019). This is believed to be partially due to evergreen trees, which secrete chemicals collectively known as phytoncides. Phytoncide is associated with improvements in human immune cell activity, particularly with enhancing human natural killer (NK) cell activity, the number of NK cells, intracellular anti-cancer proteins in lymphocytes, and significantly decreasing the concentrations of adrenaline and noradrenaline in urine (Li et al 2009). What’s more, the increased NK activity measured in both blood and urine samples lasted for more than seven days after trips to forests in both male and female subjects (Li et al 2009). Nature exposure also seems to decrease cytokines TNF-alpha, IL-6 (Sarris et al 2019), and IL-8 (Wen et al 2019), for an overall anti-inflammatory effect.
Nature Exposure Improves Mental Health
Several studies have looked at urban “greenness” and how it relates to mental health. Gascon and colleagues published a systematic review on these studies in 2015, and found though the data quality is not high, the general trajectory of the effect is that nature exposure improves mental health parameters (Corazon et al 2019, Gascon et al 2015). As an example, one such study was a large cross-sectional population study out of Wisconsin (Beyer et al 2014). They controlled for a multitude of confounding factors, including demographic data, socio-economic status, and even level of health insurance and concluded that people living in greener neighbourhoods (as measured by percentage of tree canopy) had a decreased risk of depression and anxiety. More recent studies and systematic reviews continue to corroborate these findings: access to nature improves depression and anxiety scores, alleviates anger, increases relaxation, improves sleep quality and quantity, and subjective well-being (Hansen et al 2017, Li 2019, Sarris et al 2019, Shin and Parab 2020, Wen et al 2019).
Living in a greener area seems to also improve mental health outcomes in the long run. A longitudinal study done by Alcock and colleagues (2014) showed that the mental health scores of people who moved to greener areas improved, while the scores of those who moved to less green areas deteriorated. Amongst those who moved to less green areas, the mean inverse score on the General Health Questionnaire fell from 10.15 to 9.99 right after the move, though it later rose back up, suggesting an accommodation to the new environment. No such accommodation was necessary amongst those who moved to greener areas. Their mean inverse scores rose progressively from 9.78 two years prior to the move, to 10.10 a year after the move to greener areas, and stayed there for the next two years, showing an improvement that was sustained.
Adding an outdoor component to typical interventions for mental health, such as cognitive-behavioral therapy (CBT), augmented the positive results of the intervention. Kim and colleagues (2009) undertook to compare the efficacy of CBT for major depression in hospital versus forest settings. They found that the participants who had undergone CBT in a natural setting had significantly lower depressions scores, and significantly higher remission rates. The added benefit effect is similar to what was found with outdoor versus indoor exercise. Horticultural therapy has a similar effect too. Substance abuse treatment program participants showed a trend for improvement in depression and an increase in quality of life when they combined horticultural therapy and occupational therapy, compared to just participating in the usual occupational therapy (Sarris et al 2019).
Nature Increases Cognitive Performance and Memory
Unsurprisingly at this point, some evidence suggests that nature exposure is beneficial to cognitive processes, such as working memory, cognitive flexibility, and attentional control (Stevenson et al 2018). In a 2003 trial by Hartig and colleagues, participants had to perform either a mentally taxing activity or a take a non-taxing drive to a field site. Each group was then divided and assigned to spend time in an urban environment or a natural one. The researchers measured blood pressure, affect, and performance on a memory test. The participants that got to recover in the natural setting, regardless of the initial task, had a faster decrease in blood pressure, and better performance on the memory test. Berman and colleagues (2008) did a similar study, and suggest that the reason for improved cognitive recovery in natural settings is that nature is less psychologically demanding and invokes a state of peacefulness. An urban setting demands more attention that in turn is cognitively taxing.
Nature Exposure for Children
The health of children has changed with the proliferation of urban living as much as it has for adults. Children spend increasingly more time indoors, with much of their time occupied by technology, even in school. It has been established that children’s development is enriched through contact with nature, as they have greater opportunities to be creative, curious, take risks, strengthen their sense of self, and recover from stress (Dadvand et al 2017). All of these constructs contribute to positive psychological, emotional, motor, and cognitive development (Soga and Gaston 2016a).
Generally, studies evaluating the effect of nature on children’s mental and cognitive health have been rather heterogeneous, with variable data, though the majority do show benefit (Balseviciene et al 2014, Gascon et al 2015). One study explored the potential use of ‘green space play’ to improve symptoms of ADHD. Parents of children diagnosed with ADHD were surveyed with a specially designed questionnaire. They were asked about their kids’ attention and behaviour symptoms following play in various settings and asked to rank which type of play resulted in the best and worst overall behaviour: a green setting (eg. fishing, soccer), an ambiguous setting (eg. rollerblading, playing outside), or a non-green setting (eg. video games). The findings showed that green play significantly reduced ADHD symptoms when compared to non-green play (Taylor et al 2001).
There is evidence that nature’s positive influence extends to babies in utero. Closer maternal proximity to green spaces was associated with significantly higher weight at birth, and reduced risk of low birth weight (Agay-Shay et al 2014).
Discussion
Research into the field of green spaces and nature exposure is being conducted globally, with positive associations between natural environments and human health being clearly identified. While the quantity of the data has increased, often the quality of individual studies is low. Much of the existing research is cross-sectional, observational, susceptible to socioeconomic confounders, or conducted with small sample sizes. Nonetheless, there is something to be said for the fact that the overwhelming majority of the evidence shows a positive relationship between biomarkers of health and nature exposure. Collectively, these studies confirm that being in contact with nature can reduce psychological and physical stress, improve cardiovascular risk factors, benefit adult’s and children’s mental health, reduce inflammation, boost immune function, improve antioxidant capacity, sharpen cognition, improve sleep quality, and very simply increase feelings of wellbeing.
Quite a bit of thought has been given to try and understand why such effects exist, and why it is that human beings seemingly require this connection to nature for good health. Two of these are Kaplan and Kaplan’s attention restoration theory, and Ulrich’s stress recovery theory (Bowler et al 2010, Twohig-Bennett and Jones 2018). Attention restoration postulates that natural environments provide specific stimuli that allow our cognitive attention capacity to recover from the rigors of urban life, by providing a break from our routine stresses, and allowing a ‘soft fascination’ with the environment which is not taxing on our minds. Stress recovery is a complementary theory that suggests that natural features trigger an evolutionary adaptive response that generates feelings of positive affect, safety, and survival. Both of these theories suggest that there is something about viewing features of the environment that triggers healthy responses, and some evidence suggests that it is indeed visual stimuli which play a large role. When study participants viewed virtual images of natural landscapes (computers or VR setups), they demonstrated reduced stress and increased relaxation and wellbeing compared to images of urban landscapes, or indoor settings (Browning et al 2020, Zabini et al 2020). In another study, functional MRI was used to compare brain activation when viewing images of natural and urban landscapes. It was found that Brodmann area 31 was activated only with natural images, which is associated with adjusting attention (Tang et al 2017).
Other mechanisms of how nature exposure promotes human health include the increased opportunity for physical activity, opportunity for social interaction, exposure to sunlight and vitamin D, exposure to negative ions, phytoncides, and volatile oils, and exposure to the kinds of symbiotic microorganisms that humans have evolved with (Twohig-Bennett and Jones 2018). Exposure to natural environments has been associated with higher gut microbial biodiversity, which is associated with improved immune maturation and reduced risk of immune diseases and disorders (Tasnim et al 2017). This is not seen with urban environments. In fact, urban environments are associated with health-harming factors, such as poor diets, pollution, sedentary lifestyles, and social and psychological stress (Soga et al 2016b). Humans have evolved for centuries within natural environments. If natural features are removed from the human experience, mental and physical health suffers. Take for example the data that shows that immense loss of trees from the emerald ash borer infestation in the northern US is associated with a small but significant increase in CVD and respiratory deaths in those areas (Bhatnagar 2017).
The kind of evidence discussed here hopefully makes it easy for all types of health care practitioners to begin recommending nature exposure to their patients if they aren’t already. Forests and other undeveloped areas would be most ideal, but they are not accessible to everyone. Gardening is an easy prescription for exposure to green spaces (Soga et al 2016b), which can be accessed in rural and urban areas (as private plots, container/balcony gardens, or community gardens). Urban dwellers from many socioeconomic backgrounds can find health benefits since urban parks are also effective. In the absence of urban parks, or where accessibility to them is restricted or difficult, even virtual exposure can offer some mental health support (Browning et al 2020).
Conclusion
Naturopathic medicine originated in the ‘nature cure’ traditions of European healers, to whom spending time in nature was an integral part of providing natural health care. Cultures all over the world have long recognized the importance of closeness to nature. Many of these traditions have been preserved, or are undergoing a rebirth, such as the forest bathing practices in Japan, where they have established Forest Medicine as a new interdisciplinary science (Li 2019). Certainly, naturopathic medical philosophy maintains this connection as well. However, our modern lives have led to a distancing from nature, and all of us are likely sensing the rift. The evidence that has been summarized here highlights the important health benefits that result from being in touch with natural spaces.
Having established the varied and important ways in which exposure to nature can benefit humanity, it now becomes imperative that research in this field moves to establish high quality data through standardization of methodology and greater scientific rigor. It is this level of evidence that is most likely to influence and guide policy and urban planning to adequately incorporate natural environments within cities (Nieuwenhuijsen et al 2017). In the meantime, considering especially that the level of risk is very low relative to benefit, we recommend that “Vitamin G” should make its way back to the prescription pads of every healthcare provider, particularly for those patients living in urban environments.
References
Agay-Shay K, Peled A, Crespo AV, Peretz C, Amitai Y, Linn S, Friger M, Nieuwenhuijsen MJ. Green spaces and adverse pregnancy outcomes. Occup Environ Med. 2014 Aug;71(8):562-569.
Alcock I, White MP, Wheeler BW, Fleming LE, Depledge MH. Longitudinal effects on mental health of moving to greener and less green urban areas. Environ Sci Technol. 2014; 48(2):1247-1255.
Antonelli M, Barbieri G, Donelli D. Effects of forest bathing (shinrin-yoku) on levels of cortisol as a stress biomarker: a systematic review and meta-analysis. Int J Biometeorol. 2019 Aug;63(8):1117-1134.
Balseviciene B, Sinkariova L, Grazuleviciene R, et al. Impact of residential greenness on preschool children’s emotional and behavioral problems. Int J Environ Res Public Health. 2014;11(7):6757-6770.
Barton J, Pretty J. What is the Best Dose of Nature and Green Exercise for Improving Mental Health? A Multi-Study Analysis. Environ. Sci. Technol. 2010; 44:3947–3955.
Berman MG, Jonides J, Kaplan S. The cognitive benefits of interacting with nature. Psychol Sci. 2008;19(12):1207-1212.
Beyer KM, Kaltenbach A, Szabo A, Bogar S, Nieto FJ, Malecki KM. Exposure to Neighborhood Green Space and Mental Health: Evidence from the Survey of the Health of Wisconsin. Int J Environ Res Public Health. 2014; 11(3): 3453–3472.
Bhatnagar A. Environmental Determinants of Cardiovascular Disease. Circ Res. 2017;121(2):162-180.
Bowler DE, Buyung-Ali LM, Knight TM, Pullin AS. A systematic review of evidence for the added benefits to health of exposure to natural environments. BMC Public Health. 2010;10:456.
Browning MHEM, Mimnaugh KJ, van Riper CJ, Laurent HK, LaValle SM. Can Simulated Nature Support Mental Health? Comparing Short, Single-Doses of 360-Degree Nature Videos in Virtual Reality With the Outdoors. Front Psychol. 2020;10:2667.
Coon JT, Boddy K, Stein K, Whear R, Barton J, Depledge MH. Does Participating in Physical Activity in Outdoor Natural Environments Have a Greater Effect on Physical and Mental Wellbeing than Physical Activity Indoors? A Systematic Review. Environmental Science & Technology, 2011; 45(5): 1761–1772.
Corazon SS, Sidenius U, Poulsen DV, Gramkow MC, Stigsdotter UK. Psycho-Physiological Stress Recovery in Outdoor Nature-Based Interventions: A Systematic Review of the Past Eight Years of Research. Int J Environ Res Public Health. 2019;16(10):1711.
Dadvand P, Tischer C, Estarlich M, et al. Lifelong Residential Exposure to Green Space and Attention: A Population-based Prospective Study. Environ Health Perspect. 2017;125(9):097016.
Gascon M, Triguero-Mas M, Martínez D, et al. Mental health benefits of long-term exposure to residential green and blue spaces: a systematic review. Int J Environ Res Public Health. 2015;12(4):4354-4379.
Gascon M, Triguero-Mas M, Martínez D, Dadvand P, Rojas-Rueda D, Plasència A, Nieuwenhuijsen MJ. Residential green spaces and mortality: A systematic review. Environ Int. 2016 Jan;86:60-67.
Hansen MM, Jones R, Tocchini K. Shinrin-Yoku (Forest Bathing) and Nature Therapy: A State-of-the-Art Review. Int J Environ Res Public Health. 2017;14(8):851.
Hartig T, Evans GW, Jamner LD, Davis DS, Garling T. Tracking restoration in natural and urban field settings. Journal of Environmental Psychology. 2003; 23(2):109-123.
Kim W, Lim SK, Chung EJ, Woo JM. The effect of cognitive behavior therapy-based psychotherapy applied in a forest environment on psychological changes and remission of major depression. Psychiatry Invest. 2009;6:245–254.
Li Q. Effets des forêts et des bains de forêt (shinrin-yoku) sur la santé humaine : une revue de la littérature [Effect of forest bathing (shinrin-yoku) on human health: A review of the literature]. Sante Publique. 2019 May 13;S1(HS):135-143. French.
Li Q, Kobayashi M, Wakayama Y, Inagaki H, Katsumata M, Hirata Y, Hirata K, Shimizu T, Kawada T, Park BJ, Ohira T, Kagawa T, Miyazaki Y. Effect of phytoncide from trees on human natural killer cell function. Int J Immunopathol Pharmacol. 2009;22(4):951-959.
Logan A, Selhub E. Your Brain On Nature: The Science of Nature’s Influence on Your Health, Happiness, and Vitality. Mississaugua, ON: John Wiley & Sons Canada Publisher, 2012.
Louv R. Last Child in the Woods. Saving Our Children From Nature-Deficit Disorder. Chapel Hill, NC: Algonquin Books Of Chapel Hill, 2005.
Mao GX, Cao YB, Lan XG, He ZH, Chen ZM, Wang YZ, Hu XL, Lv YD, Wang GF, Yan J. Therapeutic effect of forest bathing on human hypertension in the elderly. Journal of Cardiology. 2012;60(6):495-502.
Nieuwenhuijsen MJ, Khreis H, Triguero-Mas M, Gascon M, Dadvand P. Fifty Shades of Green: Pathway to Healthy Urban Living. Epidemiology. 2017 Jan;28(1):63-71.
Park BJ, Tsunetsugu Y, Kasentani T, Hirano H, Kagawa T, Sato M, Miyazaki Y. Physiological Effects of Shinrin-yoku (Taking in the Atmosphere of the Forest)—Using Salivary Cortisol and Cerebral Activity as Indicators. J Physiol Anthropol. 2007;26(2):123–128.
Roe JJ, Thompson CW, Aspinall PA, Brewer MJ, Duff EI, Miller D, Mitchell R, Clow A. Green space and stress: evidence from cortisol measures in deprived urban communities. Int J Environ Res Public Health. 2013;10(9):4086-4103.
Rogerson M, Wood C, Pretty J, Schoenmakers P, Bloomfield D, Barton J. Regular Doses of Nature: The Efficacy of Green Exercise Interventions for Mental Wellbeing. Int J Environ Res Public Health. 2020;17(5):1526.
Sarris J, de Manincor M, Hargraves F, Tsonis J. Harnessing the Four Elements for Mental Health. Front Psychiatry. 2019;10:256.
Shin JC, Parab KV, An R, Grigsby-Toussaint DS. Greenspace exposure and sleep: A systematic review. Environ Res. 2020 Mar;182:109081.
Soga M, Gaston KJ. Extinction of experience: the loss of human-nature interactions. Front. Ecol. Environ. 2016;14:94–101.a
Soga M, Gaston KJ, Yamaura Y. Gardening is beneficial for health: A meta-analysis. Prev Med Rep. 2016;5:92-99.b
Stevenson MP, Schilhab T, Bentsen P. Attention Restoration Theory II: a systematic review to clarify attention processes affected by exposure to natural environments. J Toxicol Environ Health B Crit Rev. 2018;21(4):227-268.
Tang IC, Tsai YP, Lin YJ, Chen JH, Hsieh CH, Hung SH, Sullivan WC, Tang HF, Chang CY. Using functional Magnetic Resonance Imaging (fMRI) to analyze brain region activity when viewing landscapes. Landscape and Urban Planning,Volume 162,2017,Pages 137-144.
Tasnim N, Abulizi N, Pither J, Hart MM, Gibson DL. Linking the Gut Microbial Ecosystem with the Environment: Does Gut Health Depend on Where We Live? Front Microbiol. 2017;8:1935.
Taylor AF, Kuo FE, Sulllivan WC. Coping with ADD: The surprising connection to green play settings. Environment and Behavior, 2001;33(1):54–77.
Tsunetsugu Y, Lee J, Park BJ, Tyrvainen L, Kagawa T, Miyazaki Y.Physiological and psychological effects of viewing urban forest landscapes assessed by multiple measurements. Landscape and Urban Planning. 2013;113:90-93.
Twohig-Bennett C, Jones A. The health benefits of the great outdoors: A systematic review and meta-analysis of greenspace exposure and health outcomes. Environ Res. 2018;166:628-637.
Van Den Berg AE, Custers MH. Gardening promotes neuroendocrine and affective restoration from stress. J Health Psychol. 2011 Jan;16(1):3-11.
Vogelzangs N, Beekman A, Milaneschi Y, Bandinelli S, Ferrucci L and Penninx B. Urinary cortisol and six-year risk of all-cause and cardiovascular mortality. J Clin Endocrinol Metab. 2010;95(11):4959–4964.
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. 2019;24(1):70.
Yeager RA, Smith TR, Bhatnagar A. Green environments and cardiovascular health. Trends Cardiovasc Med. 2020 May;30(4):241-246. Zabini F, Albanese L, Becheri FR, et al. Comparative Study of the Restorative Effects of Forest and Urban Videos during COVID-19 Lockdown: Intrinsic and Benchmark Values. Int J Environ Res Public Health. 2020;17(21):8011.