Frontiers | How might contact with nature promote human health? Promising mechanisms and a possible central pathway

Frontiers | How might contact with nature promote human health? Promising mechanisms and a possible central pathway
MINI REVIEW article
Front. Psychol.
, 25 August 2015
Sec. Cognitive Science
Volume 6 - 2015 |
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Nature and Environment: The Psychology of Its Benefits and Its Protection.
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MINI REVIEW article
Front. Psychol.
, 25 August 2015
Sec. Cognitive Science
Volume 6 - 2015 |
How might contact with nature promote human health? Promising mechanisms and a possible central pathway
Ming Kuo
Landscape and Human Health Laboratory, Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign
Urbana, IL, USA
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Abstract
How might contact with nature promote human health? Myriad studies have linked the two; at this time the task of identifying the mechanisms underlying this link is paramount. This article offers: (1) a compilation of plausible pathways between nature and health; (2) criteria for identifying a possible central pathway; and (3) one promising candidate for a central pathway. The 21 pathways identified here include environmental factors, physiological and psychological states, and behaviors or conditions, each of which has been empirically tied to nature and has implications for specific physical and mental health outcomes. While each is likely to contribute to nature’s impacts on health to some degree and under some circumstances, this paper explores the possibility of a central pathway by proposing criteria for identifying such a pathway and illustrating their use. A particular pathway is more likely to be central if it can account for the size of nature’s impacts on health, account for nature’s specific health outcomes, and subsume other pathways. By these criteria,
enhanced immune functioning
emerges as one promising candidate for a central pathway between nature and health. There may be others.
Introduction
Contact with nature has been tied to health in a plenitude of studies. Time spent in and around tree-lined streets, gardens, parks, and forested and agricultural lands is consistently linked to objective, long-term health outcomes. The less green a person’s surroundings, the higher their risk of morbidity and mortality – even when controlling for socioeconomic status and other possible confounding variables. The range of specific health outcomes tied to nature is startling, including depression and anxiety disorder, diabetes mellitus, attention deficit/hyperactivity disorder (ADHD), various infectious diseases, cancer, healing from surgery, obesity, birth outcomes, cardiovascular disease, musculoskeletal complaints, migraines, respiratory disease, and others, reviewed below. Finally, neighborhood greenness has been consistently tied to life expectancy and all-cause mortality (see Table
in the Supplementary Materials).
These findings raise the possibility that such contact is a major health determinant, and that greening may constitute a powerful, inexpensive public health intervention. It is also possible, however, that the consistent correlations between greener surroundings and better health reflect self-selection – healthy people moving to or staying in greener surroundings. Examining the potential pathways by which nature might promote health seems paramount — both to assess the credibility of a cause-and-effect link and to suggest possible nature-based health interventions. Toward that end, this article offers: (1) a compilation of plausible pathways between nature and health; (2) criteria for identifying a possible central pathway; and (3) one promising candidate for a central pathway.
How Nature Might Promote Health: Plausible Pathways
How might contact with nature promote health? To date, reviews and studies addressing multiple possible mechanisms (
Groenewegen et al., 2006
2012
Sugiyama et al., 2008
de Vries et al., 2013
Hartig et al., 2014
) have focused on four – air quality, physical activity, stress, and social integration. But the burgeoning literature on nature benefits has revealed an abundance of possible mechanisms: as
Figure
shows, this review identifies 21 plausible causal pathways from nature to health. Each has been empirically tied to contact with nature while accounting for other factors, and is empirically or theoretically tied to specific health outcomes (for details on the scope of this review, see Table
in the Supplementary Materials). The 21 pathways identified here include environmental factors, physiological and psychological states, and behaviors or conditions, and are summarized below (for more details on each of these pathways, see Table
in the Supplementary Materials).
FIGURE 1
Environmental Conditions
Some of the plausible pathways from contact with nature to improved health stem from specific environmental conditions. Natural environments contain chemical and biological agents with known health implications. Many plants give off
phytoncides
— antimicrobial volatile organic compounds — which reduce blood pressure, alter autonomic activity, and boost immune functioning, among other effects (
Komori et al., 1995
Dayawansa et al., 2003
Li et al., 2006
2009
). The air in forested and mountainous areas, and near moving water, contains high concentrations of
negative air ions
Li et al., 2010
), which reduce depression (
Terman et al., 1998
Goel et al., 2005
), among other effects (Table
in the Supplementary Materials). These environments also contain
mycobacterium vaccae
, a microorganism that appears to boost immune functioning (see
Lowry et al., 2007
for review). Similarly,
environmental biodiversity
has been proposed to play a key role in immune function via its effects on the microorganisms living on skin and in the gut, although the evidence for this is mixed (Table
in the Supplementary Materials).
The
sights
and
sounds
of nature also have important physiological impacts. Window views and images of nature reduce sympathetic nervous activity and increase parasympathetic activity (e.g.,
Gladwell et al., 2012
Brown et al., 2013
), restore attention (e.g.,
Berto, 2005
), and promote healing from surgery (
Ulrich, 1984
). Sounds of nature played over headphones increase parasympathetic activation (
Alvarsson et al., 2010
). These sympathetic and parasympathetic effects drive the immune system’s behavior (for review, see
Kenney and Ganta, 2014
), with long-term health consequences.
In built environments, trees and landscaping may promote health not only by contributing positive factors like phytoncides but also by reducing negative factors.
Air pollution
is associated with myocardial inflammation and respiratory conditions (
Villarreal-Calderon et al., 2012
).
High temperatures
can cause heat exhaustion, heat-related aggression and violence, and respiratory distress due to heat-related smog formation (
Anderson, 2001
Akbari, 2002
Tawatsupa et al., 2012
). And
violence
affects physical and mental health (e.g.,
Groves et al., 1993
). Vegetation filters pollutants from the air (although see Table
in the Supplementary Materials for details), dampens the urban heat island (e.g.,
Souch and Souch, 1993
), and appears to reduce violence (Table
in the Supplementary Materials for review).
Physiological and Psychological States
Some of the plausible pathways between contact with nature and health involve short-term physiological and psychological effects, which, if experienced regularly, could plausibly account for long-term health effects.
Blood tests before and after walks in different environments reveal that levels of health-protective factors increase after forest but not urban walks.
Didehydroepiandrosterone
(DHEA) increases after a forest walk (
Li et al., 2011
); DHEA has cardio protective, anti-obesity, and anti-diabetic properties (
Bjørnerem et al., 2004
). Similarly, time in nature increases
adiponectin
Li et al., 2011
), which protects against atherosclerosis, among other things (Table
in the Supplementary Materials), and the
immune system
’s anti-cancer (so-called “Natural Killer,” or NK) cells and related factors (Table
in the Supplementary Materials). NK cells play important protective roles in cancer, viral infections, pregnancy, and other health outcomes (
Orange and Ballas, 2006
).
Further, walks in forested, but not urban areas, reduce the levels of health risk factors, specifically inflammatory cytokines (
Mao et al., 2012
), and
elevated blood glucose
Ohtsuka et al., 1998
). Inflammatory cytokines are released by the
immune system
in response to threat, and have been implicated in diabetes, cardiovascular disease, and depression (Table
in the Supplementary Materials). Chronically elevated blood glucose carries multiple health risks, including blindness, nerve damage, and kidney failure (
Sheetz and King, 2002
). The powerful effects of a walk in a forest on blood glucose are particularly striking (Table
in the Supplementary Materials for review).
Contact with nature has a host of other physiological effects related to
relaxation
or stress reduction (Table
in the Supplementary Materials). The experience of nature helps shift individuals toward a state of deep relaxation and parasympathetic activity, which improves sleep (
El-Sheikh et al., 2013
), boosts immune function in a number of ways (
Kang et al., 2011
), and counters the adverse effects of stress on energy metabolism, insulin secretion, and inflammatory pathways (
Bhasin et al., 2013
). Evidence suggests this pathway contributes substantially to the link between nature and health (Table
in the Supplementary Materials).
Three psychological effects of nature — experiences of
awe
Shiota et al., 2007
), enhanced
vitality
Ryan et al., 2010
), and
attention restoration
(Table
in the Supplementary Materials) — offer additional possible pathways between nature and health. Regular experiences of awe are tied to healthier, lower levels of inflammatory cytokines (
Stellar et al., 2015
); the ties between nature and awe, and awe and cytokines, respectively, may help explain the effects of forest walks on cytokines above. Similarly, feelings of vitality predict resistance to infection (
Cohen et al., 2006
) and lowered risk of mortality (
Penninx et al., 2000
). Attention restoration could theoretically reduce accidents caused by mental fatigue and, by bolstering impulse control, reduce risky health behaviors such as smoking, overeating, and drug or alcohol abuse (
Wagner and Heatherton, 2010
).
Behaviors and Conditions
The remaining four possible pathways between contact with nature and health identified here involve behaviors and conditions:
physical activity
obesity
sleep
, and
social ties
. Physical activity is a major contributor to health (
Centers for Disease Control and Prevention [CDC], 2015
), and intuitively we associate green space with physical activity — but empirically this relationship is surprisingly inconsistent (Table
in the Supplementary Materials) and may hold only under certain conditions and for certain populations. Perhaps still more surprising, while greener residential areas do not consistently predict physical activity, they do consistently predict lower rates of obesity (for review, see Table
in the Supplementary Materials); this suggests the pathway between nature and obesity may depend less on nature’s effects on physical activity and more on its effects on adiponectin, stress, and impulse control. Both sleep and social ties are major contributors to health (Table
in the Supplementary Materials); contact with nature contributes to both better sleep (
Morita et al., 2011
Astell-Burt et al., 2013
) and stronger social ties (see Table
in the Supplementary Materials for review).
Exploring the Possibility of a Central Pathway
Each of the mechanisms above is likely to contribute to nature’s impacts on health to some degree and under some circumstances. Most likely, some pathways will play a larger role than others. This paper explores the possibility that one or a few pathways may explain the lion’s share of the link between nature and health by proposing criteria for identifying central pathways and illustrating the application of these criteria.
First, a pathway is more likely to be central if it can account for the size of nature’s impacts on health. A study of over 345,000 people living in greener and less green residential surroundings revealed large differences in the prevalence of disease; even after controlling for socioeconomic status, prevalence for 11 major categories of disease was at least 20% higher among the individuals living in less green surroundings (
Maas et al., 2009
). For a single pathway to plausibly account for the bulk of the tie between nature and health, the mechanism involved would need to have substantial effects on health, and be substantially affected by contact with nature.
Second, a pathway is more likely to be central if it can account for specific health outcomes tied to nature. Although health is often treated as a unitary construct in the nature-health literature, poor health takes a multiplicity of separable, largely independent forms. A pathway that leads to one health outcome may not lead to others; for example, reduced air pollution may lessen respiratory symptoms, but is not likely to affect ADHD symptoms. A central pathway between nature and health should account for many, if not most, of the specific health outcomes tied to nature.
Third, a pathway is more likely to be central if it subsumes other pathways. To the extent that multiple nature-health pathways feed into a particular pathway between nature and health, that pathway is more central to the relationship between nature and health.
These three criteria can be applied to any given pathway to determine its centrality. In this paper, they are applied to one particular pathway: enhanced immune functioning.
Criterion #1: Accounting for the Size of the Nature-Health Link
Determining whether a particular pathway can account for the size of the nature–health link requires examining the effect sizes for the nature–mechanism and mechanism–health relationships. For the immune system, the existing literature reveals both these effect sizes to be large.
Time spent in nature has substantial beneficial effects on the immune system, raising positive indicators, and lowering negative ones. Two 2-h forest walks on consecutive days increased the number and activity of anti-cancer NK cells by 50 and 56%, respectively, and activity remained significantly boosted even a month after returning to urban life — 23% higher than before the walks (
Li, 2010
). Moreover, extended time in a forest decreased inflammatory cytokines implicated in chronic disease by roughly one-half (
Mao et al., 2012
). Urban walks have no such effect.
The immune system, in turn, has powerful effects on health. The cytotoxic activity of NK cells is important in preventing cancer – in an 11-year study, the incidence of cancer among the individuals in the middle and top third of cytotoxic activity was roughly 40% less than that among individuals with low levels of NK activity (
Imai et al., 2000
). NK cells also play important health-promoting roles in fighting viral and other infections, in autoimmune disorders, and in pregnancy (see
Orange and Ballas, 2006
for review). Moreover, inflammatory cytokines are thought to play an important role in a host of chronic diseases, including diabetes, cardiovascular disease, and depression (
Cesari et al., 2003
Wellen and Hotamisligil, 2005
Dowlati et al., 2010
).
It appears that enhanced immune function fulfills the first criterion for a central pathway: it can account for the size of nature’s apparent impacts on health.
Criterion #2: Accounting for the Specific Health Outcomes Tied to Nature
Each specific health outcome tied to nature constitutes a testable hypothesis for any proposed central pathway; the more specific health outcomes a pathway can account for, the more central its role.
Contact with nature has been linked to a plethora of specific health outcomes; in general, the more contact with nature, the better the health outcome, even after controlling for socioeconomic status and other factors. For each of the following, available evidence points to a favorable impact: acute urinary tract infections, anxiety disorder, ADHD, birth outcomes, cancer, cardiovascular disease, depression, diabetes mellitus, healing from surgery, infectious disease of the intestinal canal, musculoskeletal complaints, medically unexplained physical symptoms (MUPS), migraines, upper respiratory tract infections, respiratory disease, and vertigo (for details, see Table 3 in the Supplemental Materials). For allergies, asthma, and eczema, the apparent impact of nature varies; depending on the specific measures used and the place, the relationships are positive, negative, or null (Table 3 in the Supplemental Materials).
To determine whether enhanced immune functioning could account for these specific health outcomes, the literature on immune functioning and each of the 18 specific outcomes was collected and reviewed. Available evidence indicates that enhanced immune functioning may be able to account, wholly or partially, for all 18 (see
Figure
).
FIGURE 2
One of the chief functions of the immune system is to ward off infectious disease, protecting the body from bacterial, parasitic, fungal, and viral infections (
National Institutes of Health [NIH], 2012
). Thus enhanced immune function could clearly explain why contact with nature is tied to lower rates of acute urinary tract infections, infectious disease of the intestinal canal, and upper respiratory tract infections. Further, for health outcomes with multiple possible origins, enhanced immune function can account for cases with infectious origins — for example, infectious forms of respiratory disease but perhaps not forms of respiratory disease with non-infectious origins. Similarly, enhanced immune function can account for MUPS and vertigo with infectious origins (
Bovo et al., 2006
Deary et al., 2007
, respectively).
Two other key roles of the immune system are to assist in wound healing, and to seek out and destroy tumor cells. Thus enhanced immune function can account for the effect of a hospital view of nature on recovery from surgery (
Ulrich, 1984
), as well as the relationship between residential greenness and lower rates of cancer (
Li et al., 2010
). Further, the immune system governs inflammation, which is involved in allergies (
National Institutes of Health [NIH], 2015
), anxiety disorder (
Salim et al., 2012
), asthma (
Murdoch and Lloyd, 2010
), cardiovascular disease (
Mari et al., 2002
Ho et al., 2010
Schiffrin, 2013
), depression (
Calabrese et al., 2014
), diabetes mellitus (
Pedicino et al., 2013
), eczema (
National Institutes of Health [NIH], 2014
), and musculoskeletal complaints (
Ji et al., 2002
Wang et al., 2011
). Finally, immune functioning is important in healthy birth weight (
Moffett et al., 2014
), and is suspected to play a role in ADHD (
Segman et al., 2002
Budziszewska et al., 2010
) and migraines (
Bruno et al., 2007
).
Available evidence indicates that enhanced immune function fulfills the second criterion for a central pathway.
Criterion #3: Subsuming Other Pathways between Nature and Health
A nature–health pathway is more central if it subsumes other pathways; the more other pathways it subsumes, the more central its role. As
Figure
shows, the current literature suggests enhanced immune function can subsume as many as 18 out of the 20 other possible pathways between nature and health.
Enhanced immune function is known to wholly or partially subsume 11 other pathways. Each of the following is known to enhance immune function — adiponectin (
Fantuzzi, 2013
), reduced air pollution (e.g.,
Nadeau et al., 2010
), awe (
Stellar et al., 2015
), normalized levels of blood glucose (as compared to elevated levels,
Geerlings and Hoepelman, 1999
), reduced obesity (
de Heredia et al., 2012
), physical activity (
Shepherd et al., 1991
), phytoncides (
Li et al., 2009
), better sleep (
Besedovsky et al., 2012
), social ties (
Kiecolt-Glaser et al., 2002
Robles and Kiecolt-Glaser, 2003
), relaxation and stress reduction (
Abboud et al., 2012
Bhasin et al., 2013
), and reduced immediate and long-term traumatic stress due to violence (e.g.,
Baum et al., 1993
). Note that these pathways may be partially or wholly subsumed by the enhanced immune functioning pathway between nature and health; if a pathway contributes to health via both the immune system and other effects, it is partially subsumed by the immune function pathway.
For seven additional pathways, while there is no direct evidence tying them to human immune function, there is indirect evidence suggesting such a tie. DHEA (
Hazeldine et al., 2010
), mycobacterium vaccae (
Lowry et al., 2007
), and negative air ions (
Yamada et al., 2006
) are all known to improve immune function in mice. Vitality enhances resistance to upper respiratory tract infections (see vigor findings in
Cohen et al., 2006
), an effect mostly likely mediated via enhanced immune functioning. Both visual (e.g.,
Brown et al., 2013
) and auditory (e.g.,
Alvarsson et al., 2010
) nature stimuli are likely to boost immune function by way of their demonstrated effects on parasympathetic activity, and the subsequent effects of parasympathetic activity on immune function (
Kenney and Ganta, 2014
). And environmental biodiversity has been proposed to help train and regulate the immune system, although the findings here are correlational and mixed (e.g.,
Ruokolainen et al., 2014
).
Enhanced immune function fulfills the third criterion for a central pathway.
Conclusion
This review reveals a multiplicity of mechanisms by which contact with nature might promote health, as well as a promising candidate for a central pathway. There may be other mechanisms, such as other physiological effects, reduced accidents, and healthier behaviors. There may also be other central contributors to the nature-health link – of those reviewed here, deep relaxation, attention restoration and impulse control, sleep, and social ties seem particularly worthy of attention. No doubt some of the plausible pathways identified here will prove either not to contribute substantially to nature’s impact on health, or to contribute only under certain limited circumstances; here, the roles of improved air quality, environmental biodiversity and microbiota, and physical activity merit closer study.
These limitations notwithstanding, this review makes a number of contributions to our understanding of nature and health, to future investigation in this area, and to the creation of healthy human habitats. The multiplicity of nature–health pathways identified here lends credibility to the hypothesis that nature actually promotes health, as well as a potential explanation for the startling size and scope of nature’s apparent impact. With so many contributing pathways operating in concert, the cumulative effect could be quite large even if many of the individual pathways contribute only a small effect – that is, the effect of exposure to phytoncides
plus
exposure to mycobacteria vaccae
plus
increased adiponectin
plus
stronger social ties
plus
better sleep, etc., could indeed be quite large, and if some of the pathways, such as enhanced immune function, contribute a large effect, the combined effect would be larger still.
For future work in this area, the criteria here give researchers interested in central mechanisms a means of using existing literature to assess the centrality of a particular mechanism. In addition the detailed reviews provided in the Supplementary Materials may provide a useful starting point for researchers interested in specific pathways or specific health outcomes of nature.
Finally, the findings here can help guide the creation of healthy human habitats. The existing literature speaks to the value not only of “wild” nature but also “everyday” nature – the views and green spaces where we live. That physical activity is not consistently related to greener environments suggests that our conceptualization of health-promoting greenspaces should center at least as much on oases as on ball fields, and on greenspaces for walking and quiet contemplation as much as on recreation areas. The findings here suggest that such oases should incorporate plants — especially trees, soil, and water (preferably moving) — and should be designed to induce feelings of deep relaxation, awe, and vitality. Providing these green oases, especially in areas where health risks are high and landscaping is sparse, might be an inexpensive, powerful public health intervention and address persisting health inequalities.
Statements
Acknowledgments
I am grateful to the TKF Foundation for encouragement and financial assistance in gathering some of the necessary literature for this work through its Nature Sacred National Awards program. This review is more clear, better structured, more interesting, and more complete than it would have been without the thoughtful intervention of Kirstin Wilcox, Rafter S. Ferguson, Dexter Locke, Meghan Frankel, Natalia Maurer, and reviewers Sumitava Mukherjee and Teresa Helen Horton: thank you!
Conflict of interest
The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Supplementary material
The Supplementary Material for this article can be found online at:
References
Abboud
F. M.
Harwani
S. C.
Chapleau
M. W.
2012
).
Autonomic neural regulation of the immune system: implications for hypertension and cardiovascular disease.
Hypertension
59
755
762
10.1161/HYPERTENSIONAHA.111.1868
CrossRef
Google Scholar
Akbari
H.
2002
).
Shade trees reduce building energy use and CO2 emissions from power plants.
Environ. Pollut.
116
S119
S126
10.1016/S0269-7491(01)00264-0
CrossRef
Google Scholar
Alvarsson
J. J.
Wiens
S.
Nilsson
M. E.
2010
).
Stress recovery during exposure to nature sound and environmental noise.
Int. J. Environ. Res. Public Health
1036
1046
10.3390/ijerph7031036
CrossRef
Google Scholar
Anderson
C. A.
2001
).
Heat and violence.
Curr. Dir. Psychol. Sci.
10
33
38
10.1111/1467-8721.00109
CrossRef
Google Scholar
Astell-Burt
T.
Feng
X.
Kolt
G. S.
2013
).
Does access to neighborhood green space promote a healthy duration of sleep? Novel findings from a cross-sectional study of 259 319 Australians.
BMJ Open
e003094
. doi:10.1136/bmjopen-2013-003094
Google Scholar
Baum
A.
Cohen
L.
Hall
M.
1993
).
Control, and intrusive memories as possible determinants of chronic stress.
Psychosom. Med.
55
274
286
10.1097/00006842-199305000-00005
CrossRef
Google Scholar
Berto
R.
2005
).
Exposure to restorative environments helps restore the attentional capacity.
J. Environ. Psychol.
25
249
259
10.1016/j.jenvp.2005.07.001
CrossRef
Google Scholar
Besedovsky
L.
Lange
T.
Born
J.
2012
).
Sleep and immune function.
Pflügers Arch.
463
121
137
10.1007/s00424-011-1044-0
CrossRef
Google Scholar
Bhasin
M. K.
Dusek
J. A.
Chang
B.
Joseph
M. G.
Denninger
J. W.
Fricchione
G. L.
et al
2013
).
Relaxation response induces temporal transcriptome changes in energy metabolism, insulin secretion and inflammatory pathways.
PLoS ONE
e62817
10.1371/journal.pone.0062817
CrossRef
Google Scholar
10
Bjørnerem
A.
Straume
B.
Midtby
M.
Fønnebø
V.
Sundsfjord
J.
Svartberg
J.
et al
2004
).
Endogenous sex hormones in relation to age, sex, lifestyle factors, and chronic diseases in a general population: the Tromso Study.
J. Clin. Endocrinol. Metab.
89
6039
6047
10.1210/jc.2004-0735
CrossRef
Google Scholar
11
Bovo
R.
Aimoni
C.
Martini
A.
2006
).
Immune-mediated inner ear disease.
Acta Otolaryngol.
126
1012
1021
10.1080/00016480600606723
CrossRef
Google Scholar
12
Brown
D. K.
Barton
J. L.
Gladwell
V. F.
2013
).
Viewing nature scenes positively affects recovery of autonomic function following acute-mental stress.
Environ. Sci. Technol.
47
5562
5569
10.1021/es305019p
CrossRef
Google Scholar
13
Bruno
P. P.
Carpino
F.
Carpino
G.
Zicari
A.
2007
).
An overview on immune system and migraine.
Eur. Rev. Med. Pharmacol. Sci.
11
245
248
Google Scholar
14
Budziszewska
B.
Basta-Kaim
A.
Kubera
M.
Lasoñ
W.
2010
).
Immunological and endocrinological pattern in ADHD etiopathogenesis.
Prz. Lek.
67
1200
1204
Google Scholar
15
Calabrese
F.
Rossetti
A. C.
Racagni
G.
Gass
P.
Riva
M. A.
Molteni
R.
2014
).
Brain-derived neurotrophic factor: a bridge between inflammation and neuroplasticity.
Front. Cell. Neurosci.
430
10.3389/fncel.2014.00430
CrossRef
Google Scholar
16
Centers for Disease Control and Prevention [CDC].
2015
).
Physical Activity and Health.
Available at:
Google Scholar
17
Cesari
M.
Penninx
B. W.
Newman
A. B.
Kritchevsky
S. B.
Nicklas
B. J.
Sutton-Tyrrell
K.
et al
2003
).
Inflammatory markers and onset of cardiovascular events: results from the Health ABC study.
Circulation
108
2317
2322
10.1161/01.CIR.0000097109.90783.FC
CrossRef
Google Scholar
18
Cohen
S.
Alper
C. M.
Doyle
W. J.
Treanor
J. J.
Turner
R. B.
2006
).
Positive emotional style predicts resistance to illness after experimental exposure to rhinovirus or influenza A virus.
Psychosom. Med.
68
809
815
10.1097/01.psy.0000245867.92364.3c
CrossRef
Google Scholar
19
Dayawansa
S.
Umeno
K.
Takakura
H.
Hori
E.
Tabuchi
E.
Nagashima
Y.
et al
2003
).
Autonomic responses during inhalation of natural fragrance of Cedrol in humans.
Auton. Neurosci.
108
79
86
10.1016/j.autneu.2003.08.002
CrossRef
Google Scholar
20
Deary
V.
Chalder
T.
Sharpe
M.
2007
).
The cognitive behavioural model of medically unexplained symptoms: a theoretical and empirical review.
Clin. Psychol. Rev.
27
781
797
10.1016/j.cpr.2007.07.002
CrossRef
Google Scholar
21
de Heredia
F. P.
Gómez-Martínez
S.
Marcos
A.
2012
).
Obesity, inflammation and the immune system.
Proc. Nutr. Soc.
71
332
338
10.1017/S0029665112000092
CrossRef
Google Scholar
22
de Vries
S.
van Dillen
S. M. E.
Groenewegen
P. P.
Spreeuwenberg
P.
2013
).
Streetscape greenery and health: stress, social cohesion and physical activity as mediators.
Soc. Sci. Med.
94
26
33
10.1016/j.socscimed.2013.06.030
CrossRef
Google Scholar
23
Dowlati
Y.
Herrmann
N.
Swardfager
W.
Liu
H.
Sham
L.
Reim
E. K.
et al
2010
).
A meta-analysis of cytokines in major depression.
Biol. Psychiatry
67
446
457
10.1016/j.biopsych.2009.09.033
CrossRef
Google Scholar
24
El-Sheikh
M.
Erath
S. A.
Bagley
E. J.
2013
).
Parasympathetic nervous system activity and children’s sleep.
J. Sleep Res.
22
282
288
10.1111/jsr.12019
CrossRef
Google Scholar
25
Fantuzzi
G.
2013
).
Adiponectin in inflammatory and immune-mediated diseases.
Cytokine
64
10
10.1016/j.cyto.2013.06.317
CrossRef
Google Scholar
26
Geerlings
S.
Hoepelman
A.
1999
).
Immune dysfunction in patients with diabetes mellitus.
FEMS Immunol. Med. Microbiol.
26
259
265
10.1111/j.1574-695X.1999.tb01397.x
CrossRef
Google Scholar
27
Gladwell
V. F.
Brown
D. K.
Barton
J. L.
Tarvainen
M. P.
Kuoppa
P.
Pretty
J.
et al
2012
).
The effects of views of nature on autonomic control.
Eur. J. Appl. Physiol.
112
3379
3386
10.1007/s00421-012-2318-8
CrossRef
Google Scholar
28
Goel
N.
Terman
M.
Terman
J.
Macchi
M. M.
Stewart
J. W.
2005
).
Controlled trial of bright light and negative air ions for chronic depression.
Psychol. Med.
945
955
10.1017/S0033291705005027
CrossRef
Google Scholar
29
Groenewegen
P. P.
Van den Berg
A. E.
De Vries
S.
Verheij
R. A.
2006
).
Vitamin G: effects of green space on health, well-being, and social safety.
BMC Public Health
149
10.1186/1471-2458-6-149
CrossRef
Google Scholar
30
Groenewegen
P. P.
van den Berg
A. E.
Maas
J.
Verheij
R. A.
de Vries
S.
2012
).
Is a green residential environment better for health? If so, why?
Ann. Assoc. Am. Geogr.
102
996
1003
10.1080/00045608.2012.674899
CrossRef
Google Scholar
31
Groves
B.
Zuckerman
B.
Marans
S.
1993
).
Silent victims: children who witness violence.
JAMA
262
265
10.1001/jama.1993.03500020096039
CrossRef
Google Scholar
32
Hartig
T.
Mitchell
R.
De Vries
S.
Frumkin
H.
2014
).
Nature and health.
Annu. Rev. Public Health
35
207
228
10.1146/annurev-publhealth-032013-182443
CrossRef
Google Scholar
33
Hazeldine
J.
Arlt
W.
Lord
J. M.
2010
).
Dehydroepiandrosterone as a regulator of immune cell function.
J. Steroid Biochem. Mol. Biol.
120
127
136
10.1016/j.jsbmb.2009.12.016
CrossRef
Google Scholar
34
Ho
R.
Neo
L.
Chua
A.
2010
).
Research on psychoneuroimmunology: does stress influence immunity and cause coronary artery disease?
Ann. Acad. Med.
39
191
196
Google Scholar
35
Imai
K.
Matsuyama
S.
Miyake
S.
Suga
K.
Nakachi
K.
2000
).
Natural cytotoxic activity of peripheral-blood lymphocytes and cancer incidence: an 11-year follow-up study of a general population.
Lancet
356
1795
1799
10.1016/S0140-6736(00)03231-1
CrossRef
Google Scholar
36
Ji
H.
Ohmura
K.
Umar
M.
2002
).
Arthritis critically dependent on innate immune system players.
Immunity
16
157
168
10.1016/S1074-7613(02)00275-3
CrossRef
Google Scholar
37
Kang
D. H.
McArdle
T.
Park
N. J.
Weaver
M. T.
Smith
B.
Carpenter
J.
2011
).
Dose effects of relaxation practice on immune responses in women newly diagnosed with breast cancer: an exploratory study.
Oncol. Nurs. Forum
38
E240
E252
10.1188/11.ONF.E240-E252
CrossRef
Google Scholar
38
Kenney
M. J.
Ganta
C. K.
2014
).
Autonomic nervous system and immune system interactions.
Compr. Physiol.
1177
1200
10.1002/cphy.c130051
CrossRef
Google Scholar
39
Kiecolt-Glaser
J. K.
McGuire
L.
Robles
T. F.
Glaser
R.
2002
).
Psychoneuroimmunology and psychosomatic medicine: back to the future.
Psychosom. Med.
64
15
28
10.1097/00006842-200201000-00004
CrossRef
Google Scholar
40
Komori
T.
Fujiwara
R.
Tanida
M.
Nomura
J.
Yokoyama
M. M.
1995
).
Effects of citrus fragrance on immune function and depressive states.
Neuroimmunomodulation
174
180
10.1159/000096889
CrossRef
Google Scholar
41
Li
Q.
2010
).
Effect of forest bathing trips on human immune function.
Environ. Health Prev. Med.
15
17
10.1007/s12199-008-0068-3
CrossRef
Google Scholar
42
Li
Q.
Kobayashi
M.
Inagaki
H.
Hirata
Y.
Hirata
K.
Li
Y. J.
et al
2010
).
A day trip to a forest park increases human natural killer activity and the expression of anti-cancer proteins in male subjects.
J. Biol. Regul. Homeost. Agents
24
157
165
Google Scholar
43
Li
Q.
Kobayashi
M.
Wakayama
Y.
Inagaki
H.
Katsumata
M.
Hirata
Y.
et al
2009
).
Effect of phytoncide from trees on human natural killer cell function.
Int. J. Immunopathol. Pharmacol.
22
951
959
Google Scholar
44
Li
Q.
Nakadai
A.
Matsushima
H.
Miyazaki
Y.
Krensky
A. M.
Kawada
T.
et al
2006
).
Phytoncides (wood essential oils) induce human natural killer cell activity.
Immunopharmacol. Immunotoxicol.
28
319
333
10.1080/08923970600809439
CrossRef
Google Scholar
45
Li
Q.
Otsuka
T.
Kobayashi
M.
Wakayama
Y.
Inagaki
H.
Katsumata
M.
et al
2011
).
Acute effects of walking in forest environments on cardiovascular and metabolic parameters.
Eur. J. Appl. Physiol.
111
2845
2853
10.1007/s00421-011-1918-z
CrossRef
Google Scholar
46
Lowry
C. A.
Hollis
J. H.
de Vries
A.
Pan
B.
Brunet
L. R.
Hunt
J. R. F.
et al
2007
).
Identification of an immune-responsive mesolimbocortical serotonergic system: potential role in regulation of emotional behaviour.
Neuroscience
146
756
772
10.1016/j.neuroscience.2007.01.067
CrossRef
Google Scholar
47
Maas
J.
Verheij
R. A.
de Vries
S.
Spreeuwenberg
P.
Schellevis
F. G.
Groenewegen
P. P.
2009
).
Morbidity is related to a green living environment.
J. Epidemiol. Community Health
63
967
973
10.1136/jech.2008.079038
CrossRef
Google Scholar
48
Mao
G.
Cao
Y.
Lan
X.
He
Z.
Chen
Z.
Wang
Y.
et al
2012
).
Therapeutic effect of forest bathing on human hypertension in the elderly.
J. Cardiol.
60
495
502
10.1016/j.jjcc.2012.08.003
CrossRef
Google Scholar
49
Mari
D.
Di Berardino
F.
Cugno
M.
2002
).
Chronic heart failure and the immune system.
Clin. Rev. Allergy Immunol.
23
325
340
10.1385/CRIAI:23:3:325
CrossRef
Google Scholar
50
Moffett
A.
Hiby
S. E.
Sharkey
A.
2014
).
The role of the maternal immune system in the regulation of human birth weight.
Philos. Trans. R. Soc. B Biol. Sci.
370
20140071
10.1098/rstb.2014.0071
CrossRef
Google Scholar
51
Morita
E.
Imai
M.
Okawa
M.
Miyaura
T.
Miyazaki
S.
2011
).
A before and after comparison of the effects of forest walking on the sleep of a community-based sample of people with sleep complaints.
Biopsychosoc. Med.
13
10.1186/1751-0759-5-13
CrossRef
Google Scholar
52
Murdoch
J. R.
Lloyd
C. M.
2010
).
Chronic inflammation and asthma.
Mutat. Res.
690
24
39
10.1016/j.mrfmmm.2009.09.005
CrossRef
Google Scholar
53
Nadeau
K.
McDonald-Hyman
C.
Noth
E. M.
Pratt
B.
Hammond
S. K.
Balmes
J.
et al
2010
).
Ambient air pollution impairs regulatory T-cell function in asthma.
J. Allergy Clin. Immunol.
126
845
852
10.1016/j.jaci.2010.08.008
CrossRef
Google Scholar
54
National Institutes of Health [NIH].
2012
).
What are the Health Risks of Overweight and Obesity?
Available at:
Google Scholar
55
National Institutes of Health [NIH].
2014
).
Eczema.
Available at:
Google Scholar
56
National Institutes of Health [NIH].
2015
).
Immune System.
Available at:
Google Scholar
57
Ohtsuka
Y.
Yabunaka
N.
Takayama
S.
1998
).
Shinrin-yoku (forest-air bathing and walking) effectively decreases blood glucose levels in diabetic patients.
Int. J. Biometeorol.
41
125
127
10.1007/s004840050064
CrossRef
Google Scholar
58
Orange
J. S.
Ballas
Z. K.
2006
).
Natural killer cells in human health and disease.
Clin. Immunol.
118
10
10.1016/j.clim.2005.10.011
CrossRef
Google Scholar
59
Pedicino
D.
Liuzzo
G.
Trotta
F.
Giglio
A. F.
Giubilato
S.
Martini
F.
et al
2013
).
Adaptive immunity, inflammation, and cardiovascular complications in type 1 and type 2 diabetes mellitus.
J. Diabetes Res.
2013
184258
10.1155/2013/184258
CrossRef
Google Scholar
60
Penninx
B. W. J. H.
Guralnik
J. M.
Bandeen-Roche
K.
Kasper
J. D.
Simonsick
E. M.
Ferrucci
L.
et al
2000
).
The protective effect of emotional vitality on adverse health outcomes in disabled older women.
J. Am. Geriatr. Soc.
48
1359
1366
10.1111/j.1532-5415.2000.tb02622.x
CrossRef
Google Scholar
61
Robles
T. F.
Kiecolt-Glaser
J. K.
2003
).
The physiology of marriage: pathways to health.
Physiol. Behav.
79
409
416
10.1016/S0031-9384(03)00160-4
CrossRef
Google Scholar
62
Ruokolainen
L.
von Hertzen
L.
Fyhrquist
N.
Laatikainen
T.
Lehtomäki
J.
Auvinen
P.
et al
2014
).
Green areas around homes reduce atopic sensitization in children.
Allergy
70
195
202
10.1111/all.12545
CrossRef
Google Scholar
63
Ryan
R. M.
Weinstein
N.
Bernstein
J.
Brown
K. W.
Mistretta
L.
Gagne
M.
2010
).
Vitalizing effects of being outdoors and in nature.
J. Environ. Psychol.
30
159
168
10.1016/j.jenvp.2009.10.009
CrossRef
Google Scholar
64
Salim
S.
Chugh
G.
Asghar
M.
2012
).
Inflammation in anxiety.
Adv. Protein Chem. Struct. Biol.
88
25
10.1016/B978-0-12-398314-5.00001-5
CrossRef
Google Scholar
65
Schiffrin
E. L.
2013
).
The immune system: role in hypertension.
Can. J. Cardiol.
29
543
548
10.1016/j.cjca.2012.06.009
CrossRef
Google Scholar
66
Segman
R. H.
Meltzer
A.
Gross-Tsur
V.
Kosov
A.
Frisch
A.
Inbar
E.
et al
2002
).
Preferential transmission of interleukin-1 receptor antagonist alleles in attention deficit hyperactivity disorder.
Mol. Psychiatry
72
74
10.1038/sj.mp.4000919
CrossRef
Google Scholar
67
Seguin
J.
2008
).
Human Health in a Changing Climate: A Canadian Assessment of Vulnerabilities and Adaptive Capacity.
Ottawa
Health Canada
Google Scholar
68
Sheetz
M. J.
King
G. L.
2002
).
Molecular understanding of hyperglycemia’s adverse effects for diabetic complications.
JAMA
288
2579
2588
10.1001/jama.288.20.2579
CrossRef
Google Scholar
69
Shepherd
R. J.
Verde
T. J.
Thomas
S. G.
Shek
P.
1991
).
Physical activity and the immune system.
Can. J. Sport Sci.
16
169
185
Google Scholar
70
Shiota
M. N.
Keltner
D.
Mossman
A.
2007
).
The nature of awe: elicitors, appraisals, and effects on self-concept.
Cogn. Emot.
21
944
963
10.1080/02699930600923668
CrossRef
Google Scholar
71
Souch
C. A.
Souch
C.
1993
).
The effect of trees on summertime below canopy urban climates: a case study, Bloomington, Indiana.
J. Arboric.
19
303
312
Google Scholar
72
Stellar
J. E.
John-Henderson
N.
Anderson
C. L.
Gordon
A. M.
McNeil
G. D.
Keltner
D.
2015
).
Positive affect and markers of inflammation: discrete positive emotions predict lower levels of inflammatory cytokines.
Emotion
15
129
133
10.1037/emo0000033
CrossRef
Google Scholar
73
Sugiyama
T.
Leslie
E.
Giles-Corti
B.
Owen
N.
2008
).
Associations of neighbourhood greenness with physical and mental health: do walking, social coherence and local social interaction explain the relationships?
J. Epidemiol. Community Health
62
10.1136/jech.2007.064287
CrossRef
Google Scholar
74
Tawatsupa
B.
Yiengprugsawan
V.
Kjellstrom
T.
Seubsman
S.
Sleigh
A.
2012
).
Heat stress, health and well-being: findings from a large national cohort of Thai adults.
BMJ Open
e001396
10.1136/bmjopen-2012-001396
CrossRef
Google Scholar
75
Terman
M.
Terman
J. S.
Ross
D. C.
1998
).
A controlled trial of timed bright light and negative air ionization for treatment of winter depression.
Arch. Gen. Psychiatry
55
875
882
10.1001/archpsyc.55.10.875
CrossRef
Google Scholar
76
Ulrich
R. S.
1984
).
View through a window may influence recovery from surgery.
Science
224
420
421
10.1126/science.6143402
CrossRef
Google Scholar
77
Villarreal-Calderon
R.
Reed
W.
Palacios-Moreno
J.
Keefe
S.
Herritt
L.
Brooks
D.
et al
2012
).
Urban air pollution produces up-regulation of myocardial inflammatory genes and dark chocolate provides cardioprotection.
Exp. Toxicol. Pathol.
64
297
306
10.1016/j.etp.2010.09.002
CrossRef
Google Scholar
78
Wagner
D. D.
Heatherton
T. F.
2010
). “
Giving in to temptation: the emerging cognitive neuroscience of self-regulatory failure
,” in
Handbook of Self-Regulation: Research, Theory, and Applications
2nd Edn
eds
Vohs
K. D.
Baumeister
R. F.
New York, NY
Guilford Press
41
63
Google Scholar
79
Wang
Q.
Rozelle
A. L.
Lepus
C. M.
Scanzello
C. R.
Song
J. J.
Larsen
D. M.
et al
2011
).
Identification of a central role for complement in osteoarthritis.
Nat. Med.
17
1674
1679
10.1038/nm.2543
CrossRef
Google Scholar
80
Wellen
K. E.
Hotamisligil
G. S.
2005
).
Inflammation, stress, and diabetes.
J. Clin. Invest.
115
1111
1119
10.1172/JCI200525102
CrossRef
Google Scholar
81
Yamada
R.
Yanoma
S.
Akaike
M.
Tsuburaya
A.
Sugimasa
Y.
Takemiya
S.
et al
2006
).
Water-generated negative air ions activate NK cell and inhibit carcinogenesis in mice.
Cancer Lett.
239
190
197
10.1016/j.canlet.2005.08.002
CrossRef
Google Scholar
Summary
Keywords
natural environment
greenspace
immune
mechanism
mental health
literature review
Citation
Kuo M (2015)
How might contact with nature promote human health? Promising mechanisms and a possible central pathway
Front. Psychol.
6:1093. doi:
10.3389/fpsyg.2015.01093
Received
04 March 2015
Accepted
16 July 2015
Published
25 August 2015
Volume
6 - 2015
Edited by
Marc Glenn Berman, The University of Chicago, USA
Reviewed by
Sumitava Mukherjee, Indian Institute of Management, Ahmedabad, India; Teresa Helen Horton, Northwestern University, USA
Updates
This is an open-access article distributed under the terms of the
Creative Commons Attribution License (CC BY)
. The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence:
Ming Kuo, Landscape and Human Health Laboratory, Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, 1101 West Peabody Drive, MC-637 Urbana, IL 61801, USA,
fekuo@illinois.edu
This article was submitted to Cognitive Science, a section of the journal Frontiers in Psychology
Disclaimer
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.
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