walking green: developing an evidence-base for nature
TRANSCRIPT
Walking Green Developing an Evidence-base for Nature Prescriptions in the Forest Preserves of Cook County
March 12, 2018
Technical Report
for
Walking Green:
Developing an evidence-base for Nature Prescriptions
Principal Investigator
Teresa H. Horton, PhD
Associate Professor of Research
E2HD*
Department of Anthropology
Northwestern University
Email: [email protected]
Phone: 847-467-1686
*Formerly the Laboratory for Human Biology Research
Mailing Address:
Department of Anthropology, 1810 Hinman Ave., Evanston, IL 60208
Telephone: 847-467-1686
Email: [email protected]
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Executive Summary Partially supported by the Forest Preserves of Cook County’s (FPCC) Early Action Seed Fund, Dr. Teresa Horton, Ph.D. with the Department of Anthropology, Northwestern University implemented a study to
help advance the Next Century Conservation Plan http://nextcenturyconservationplan.org/ of the FPCC. Specifically, the project aimed to provide data essential to the development of nature prescriptions (NRx) that could be used to encourage people to get outdoors and enjoy and care for nature. NRx are recommendations made by a physician to a patient to spend time outdoors in nature. In order for physicians and health care agencies to adopt NRx it is essential to demonstrate that the benefits of exercising in nature exceed those of an equivalent amount of exercise in other conditions. In this case we compared walking in Harms Woods Forest Preserve to walking on the sidewalk of Old Orchard and to the activities of daily living (ADL). Harms Woods Forest Preserve and Old Orchard Road are located in northern Cook County.
The results of this study are the first comparing both the psychological and physiological effects of walking in nature as compared to walking on a suburban sidewalk. In accordance with the National Institutes of Health guidelines for the inclusion of women and minorities in clinical research, this study explicitly tested for differences in responses by men and women, ages 18-35. The study also recruited an ethnically diverse population of participants (5% African-American; 52.5% Asian; 10.5% Hispanic; 31.5% White non-Hispanic).
Participant walking at Harms Woods Participant walking along Old Orchard Road
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These data demonstrate that the body of literature attesting to the psychological and physiological health benefits of walking in nature, literature derived primarily from research in Japan, Korea, and Taiwan, also applies to walking in the Forest Preserves of Cook County. We analyzed our data looking for differences between males and females and did not find significant differences between the sexes, thus the health benefits of nature accrue equally to men and women. We learned that:
Significant mental health benefits including improved mood, reduced anxiety, and reductions in perceived stress can be gained from taking a 50-minute walk on a Forest Preserve trail. Most importantly for residents of Cook County, these benefits are maintained even when a person spends 20 minutes driving each way to and from a Forest Preserve.
Taking a series of three 50-minute walks on a Forest Preserve trail leads to a significant increase in a person’s sense of connectedness to nature; a benefit we hope will encourage participants to engage in pro-environmental behaviors in the future.
Finally, we observed that people who started the study with fasting blood glucose levels in the range indicative of pre-diabetes showed a reduction in their blood glucose levels after completing a series of three 50-minute walks on the Forest Preserve trail. Although the number of individuals was too small to yield statistically significant differences, the results are exciting.
Our next study will follow up on this observation by recruiting subjects diagnosed with pre-diabetes to determine:
1. If walking in nature is an effective therapy for reducing blood glucose, and 2. Whether the effects of walking in nature on glucose are mediated by a reduction in anxiety
Scenery along Old Orchard Road Scenery at Harms Woods
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and perceived stress. This follow-up study will be done in conjunction with local hospitals and primary care clinics.
By working with local physicians we hope to increase their experience with research on the health benefits of nature. We also hope that by exposing more physicians and health care organizations to the results of this research, they will adopt NRx as part of their treatment formulary. For more information or to request a copy of the technical report, please contact Dr. Horton at
[email protected]. For more information on how you and your community can get healthy in the Forest Preserves of Cook
County, please contact Lydia Uhlir at [email protected]. For general information on the
Forest Preserves please visit www.fpdcc.com.
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About this report
The award from the FPCC supporting this project ended on 30 June 2017, however data collection continued until the end of August 2017 with support from additional sources. This project has yielded a very large data set. This report provides a summary of what we have found as of 31 January 2018. Supplements to this report will be submitted as more analyses are conducted, results are finalized, and manuscripts submitted for publication to professional journals. The results presented herein should be considered preliminary. Following peer review and acceptance for publication at a professional journal results will be considered final.
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Table of Contents
Executive Summary i
About this report iv
Introduction 1
Specific goal of the project 1
Background 1
The Health Benefits of Nature 1
Addressing Significant Public Health Concerns through Access to Nature 2
Study Design and Methods 3
Results 4
1. Recruitment and Retention 4
1.a Rationale: 4
1.b Results: 4
1.c. Conclusions and Lessons Learned: Recruitment and Retention 5
2. Psychological Indicators of Stress and Anxiety 6
2.a Rationale: 6
2.b Results: 7
2.c Conclusions and Lessons Learned: Psychological Indicators of Stress and Anxiety 8
3 Connecting with Nature 8
3.a Rationale: 8
3.b Results: 9
3.c Conclusions and Lessons Learned: Connecting with nature 9
4. Anthropometrics 10
4.a Rationale: 10
4.b. Results: 10
4.c. Conclusions and Lessons Learned: Anthropometrics 10
5. Biomarkers of Physiological Change 10
5.a Rationale: 10
5.b Results 11
5.c Conclusions and Lessons Learned: Biomarkers of Physiological Change 13
Summary 13
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Future directions 14
Presentations Made and Meeting Abstracts Submitted 14
Additional Funding Sources 14
Acknowledgements 14
Literature Cited 15
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Introduction
Specific goal of the project
The motivation for this project was provided by the Forest Preserves of Cook County Next Century Conservation Plan (NCCP) [1]. Goal 2/People of the NCCP states that the FPCC will use information about the health benefits of nature to encourage people of diverse communities to visit the Preserves and offer programs that emphasize the health benefits of nature ([1] pp 2, 4, 30-36). This study was designed to evaluate the efficacy of walking in the Forests Preserves to produce psychological and physiological changes leading to improved health outcomes. This information could then be used to aid the development of evidence-based nature prescriptions (NRx).
NRx are recommendations made by a physician to a patient to spend time outdoors in nature. The accumulating data which reveal the health benefits of engaging with nature have caused many local, state and national agencies to re-thinking the design of urban environments and consider conservation and creation of green space as ways to promote public health and well-being [2-8]. In 2013 the American Public Health Association issued a policy statement calling for increased access to nature as a means to improve public health and wellness [8]. Similarly, the Forest Preserves of Cook County (FPCC) in its Next Century Conservation Plan states that maintaining natural areas within the urban environment of Chicago and Cook County is essential to sustaining the health and well-being of the community and its citizens. However, the evidence needed to support claims that engaging with nature alleviates specific disorders and improves well-being, evidence essential to gaining support from physicians and health-care providers to write NRx, are limited [2, 3, 9, 10].
The absence of an evidence base demonstrating the improved efficacy of NRx relative to the usual standards of care (e.g., get more exercise) prevent health care providers from using NRx [11, 12]. To overcome these limitations, this research project combined the experience and expertise of researchers from multiple fields, including but not limited to biological anthropology, ecological physiology, endocrinology, horticultural therapy, and psychology, to investigate the pathways by which exposure to natural environments enhances human health and well-being. We compared psychological and physiological measures from participants as they went about their activities of daily living, took three 50-minute walks on a sidewalk (“increased physical activity” = usual standard of care), and three 50-minute walks on a Forest Preserve path. We tested the hypothesis that walking on the Forest Path would lead to greater improvements in mood and reductions in perceived stress as compared to walking on the sidewalk. We also wished to evaluate the feasibility of making multiple anthropometric and physiological measurements as part of a longitudinal study prior to embarking on a longer term study.
Background
The Health Benefits of Nature
“Go get some fresh air and exercise” is a common recommendation to someone who is feeling poorly, regardless of whether they are depressed, stressed, or lethargic. Just as animals removed from their natural habitats may become ill and show distressing behaviors, many of the chronic, noninfectious diseases of humans living in urban environments today may reflect living in conditions that are not the optimal environment for humans [7, 13, 14]. Increasingly, scientific studies suggest that natural environments have effects on health and well-being through a complex set of psychological and physiological interactions that act through many mechanisms [6, 9, 15, 16]. There are four over-arching
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hypotheses that describe the diverse mechanisms by which nature may improve health and well-being (summarized in [2]): 1. Increased physical activity; 2. The Attention Restoration Hypothesis, 3: The Stress Recovery Theory, and 4. The Social Cohesion Hypothesis. The stress recovery theory proposes that elements in the natural environment act through the autonomic nervous system (i.e., the mechanism responsible for the “fight or flight” and “restorative” responses) to provoke pleasant emotional responses that overcome stressful psychological states [13, 17-21]. Additionally exposure to the bright daylight of the outdoors improves mood, metabolism, circadian rhythms, and sleep [22-25].This study examined the possibility that the stress reducing effects of nature synergize with increased physical activity to improve measures of psychological and physiological health and well-being.
Addressing Significant Public Health Concerns through Access to Nature
The population of the United States and much of the world is in the midst of an obesity epidemic. More than one third (36.5%) of American adults and 17% of children (aged 2-19) are obese [26, 27]. Obesity is a risk factor for many diseases including heart-disease, stroke, type 2 diabetes and several types of cancer. The Centers for Disease Control and Prevention estimate that the annual medical cost of obesity in the U.S. in 2008 was $147 billion, and this number does not include the economic cost of lost wages and productivity due to illness and absenteeism [26]. The National League of Cities estimates that 21% of all medical spending in the United States is directed to obesity related diseases [28, 29] The obesity epidemic is caused primarily by increased availability of calorically dense foods and decreased physical activity in our daily lives as a result of changes in food quality, food availability, and social environment [26, 30] (Figure 1). However, the chronic stress of urban life may also be a contributing factor [31, 32] (Figure 1).
The regulation of body weight and composition (i.e., relative amounts of muscle to fat) is controlled by the nervous, endocrine, and immune systems [33-35]. The intricate balance of chemical signals that regulates food consumption, energy expenditure, body weight and composition is disrupted by chronic stress and inflammation. The stress response is a generalized response of the body to a “physical, chemical, biological, or psychological entity” (i.e. stressor) [36]. Changes in secretion of the stress hormone cortisol are a classic example of the stress response [36-38]. The stress response prepares the body to survive periods of famine by stimulating food intake, especially of food high in sucrose and fat, and reducing metabolic rate (the famine response) [39-41]. However, in our modern environment where calorically-dense foods are readily available, the stress response leads to abdominal obesity which is associated with cardiovascular disease and type 2 diabetes [31, 42, 43] We now know that the stress response is intimately associated with inflammatory responses and is associated with increased risk of depression, obesity and diabetes (type 1 and
Figure 1. Conceptual model illustrating the relationship between the built and social environments, diet, chronic social stress, physical activity and body mass index (BMI). BMI is commonly used measure to identify overweight and obese individuals.
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type 2), and asthma [44-48]. Thus, the reversal of the obesity epidemic and the diseases associated with it may be possible through changes in life-style that increase physical activity, decrease caloric consumption, but also reduce stress [49]. These changes in life-style are likely to be easier, and may even require, increased access to nature [30, 50].
Study Design and Methods
All procedures were approved by the Institutional Review Board (IRB) of Northwestern University (Protocol # STU 00201604). Participants reviewed the informed consent form with the investigator on Day 1 (Figure 2). They were encouraged to ask questions about the study to make sure they understood the procedures. After any questions were answered by the investigator participants signed the consent document thereby documenting their consent to participate in the study.
Based on previous research by others (see summary of current literature in Frumkin et al. 2017, [9]), we predicted that walking on a forest trail would lead to greater reductions in stress and improved physiological measures as compared to walking on a suburban sidewalk. We tested these predictions using a repeated measures cross-over design which permits longitudinal assessment of the effects of walking in different locations. Repeated measures analysis of variance and fixed-effects linear regression models were used to test for statistical significance.
Details of the methods used for all assessments are available upon request and will be included in manuscripts submitted for publication. Copies of manuscripts will be sent to the FPCC as they are accepted for publication at the appropriate professional journals.
Subjects took three 50 minute walks per week for two weeks. At the beginning of the study participants were randomly assigned to take the first series of three walks on either a suburban sidewalk (along Old Orchard Rd. from Harms Road) or forest trail (North Branch Trail from Harms Woods). Walks for both locations started from the parking lot for Grove 5 of Harms Woods. Each participant walked for a total of 50 minutes, 25 minutes out along the assigned route, then 25 minutes back to return to the start site. After taking a week off, they took three walks in the other location (Figure 2). A detailed timeline of the events that occurred on the first day of each week (days 8, 15, 22, and 29) is shown in Figure 3.
To minimize participant fatigue, and because some measures were not expected to change on a day-to-day basis, not all tests and measurements were conducted at health assessment. The complete schedule for all procedures is shown in Table 1.
Figure 2. Experimental Design. ADL = activities of daily living, Day = day of the experiment. HA = health assessment. W = walk. Arrows indicate when components of each health assessment were done. On days 15 and 29 when subjects did not walk, they left the laboratory for 2 hours to engage in ADL between the two parts of the health assessment.
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Results
1. Recruitment and Retention
1.a Rationale: One concern for longitudinal research projects is the ability to recruit and retain participants. The Walking Green protocol was particularly time consuming for the participants. It required the participants to visit the laboratory 7 times over 29 days (Figure 2). Some of the visits (Days 8, 15, 22 and 29, Figure 3) lasted 3.5 to 4 hours from the time the participant arrived in the laboratory, underwent the first part of the health assessment, went for the walk or participated in activities of daily living, then returned to the laboratory to complete the second half of the health assessment. We estimated the total time a person committed to the study was 23 hours. Therefore we were concerned about our ability to recruit and retain participants.
Our goal was to recruit 20 males and 20 females. With the exception of research focused specifically on women’s reproductive health, women are underrepresented in research studies. Because there are known gender differences in rates of depression, anxiety and other measures to be evaluated in this study, we wished to enroll equal numbers of men and women to allow us to determine if there are gender differences in the response to walking in nature.
We recruited participants by placing posters announcing the study around the campus of Northwestern University and the surrounding area in Evanston, IL. The same information was also distributed by social media (Facebook, Craig’s List) and several email listservs. Participants were also asked to provide information about the study to their friends (i.e. snowball sampling).
1.b Results: We screened 80 people to verify that they met the target audience for the study and
provided them with information about the study. Of those screened, only 2 did not fit the requirementsfor participating in the study (between 18 and 35 years of age and in good health as determined by self-assessment using the Physical Activity Readiness Questionnaire [51, 52]). Only 41 (51%) of the eligiblecontacts enrolled in the study, 21 women and 20 men. It took 14 months to recruit the desired numberof participants.
Figure 3. Daily timeline for days when blood samples and anthropometrics were conducted (Days 8, 15, 22, 29). No walks were taken on days 15 and 29 (top). Walks were taken on days 8 and 22 (bottom).
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Table 1 Schedule for testing and measurements. “x” indicates days on which a procedure was performed.
Activity 1 7 8 10 12 14 15 21 22 24 26 28 29
Informed Consent Interview x
Demographic Information x
Walk x x x x x x
Anthropometrics
Height (cm) x
Body mass (kg) x x x x x
percent body fat x x x x x
hip/waist ratio x x x x x
Physiological Measurements
Blood pressure (mm Hg) x x x x x
Heart Rate (bpm) x x x x x
Heart Rate Variation x x x x x x x
Fasting Blood Glucose x x x x
Dried blood spot (for immune
markers) x x x x
Saliva (for cortisol x x x x x x
Psychological Measures
Backward digit span (visual) x x x x x x x
Positive and Negative Affect
Scale x x x x x x x
Center for Epidemiological
Studies Depression Scale x x x x x
State Anxiety Inventory x x x x x x x
Trait Anxiety Inventory x x x x x
Cohen's Perceived Stress Scale x x x x x x x
UCLA Percieved Isolation Scale x x x x x
Nature Relatedness Scale
(NR-6) x x x x x
Experiment Day
Of the 41 people recruited, 38 (20 women and 18 men) completed the study (Table 2). It is interesting to note that all three people who dropped out after starting the study were participants who were assigned to walk on the sidewalk for the first series of walks. The majority of the participants were full-time students, either graduate or undergraduate, at Northwestern University. In addition to being full time students many of them also worked part- or full-time. Over 50% of the participants were Asian or Asian-American, no African-American women and 2 African-American men (11%) participated. Approximately 10% of the participants were Hispanic; 35% of the women and 28% of the men were white of non-Hispanic origin. Considerably more of the participants spent their childhoods in suburban and urban rather than in rural locations. All currently live in suburban or urban locations.
1.c. Conclusions and Lessons Learned: Recruitment and Retention
Recruiting participants for a longitudinal and time intensive study took considerably longer and required larger incentives than we originally anticipated. We initially planned to complete enrollment for the study in the autumn of 2016, but did not complete enrollment and data collection until mid-August 2017. Women were much more willing to volunteer for the study than men. Of the first 20 subjects 14 (70%) were female. Also, men were more likely to drop out of the study. All participants received cash
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payments as a thank-you gift for participating in the study. The initial compensation rate was $140.00 if the person completed the whole study. Pro-rated over the average time commitment for the study (23 hours), this equated to a rate of approximately $6.00/hour. In the spring of 2017 were able to increase the amount of compensation to a total of $207.0, which equates to $9.00/hour, slightly more than the local minimum wage of $8.25/hour. This resulted in an increase in the number of men recruited for the study.
Conventional thinking in the research ethics community is that the participants are engaging in the project because of their interest contributing to the “greater good” rather than to receive payment. However our experience, and those of others with whom we have spoken, indicate that while women may be motivated by scientific interest, the men are doing it for the money. The guidelines for compensating participants in research suggest that the amount to be offered should not be coercive [53, 54]. Thus our recommendation for future studies is that the compensation level be set at an amount slightly above the local minimum wage so that it is not coercive, but is sufficient to compensate people for their time [53, 54].
2. Psychological Indicators of Stress and Anxiety
2.a Rationale:
Previous studies have shown the psychological benefits of walking in nature [55-57], however these studies have not included control groups to assess the changes in psychological state that occur over the course of a day as a person goes about their activities of daily life. Nor have the studies linked the acute changes in psychological state to persistent changes in mental or physical health. To support the claim that walking in the Forest Preserves is beneficial to our mental health, it is essential to demonstrate that the changes that result from walking in the woods are not only better than those resulting from walking on the sidewalk, but are also better than going about the activities of daily living.
Also, residents of Cook County often must drive or take public transportation to reach a Forest Preserve, only one study (Bratman et al. 2015, [55]) drove their participants to and from the location of the walks between psychological assessments. Other studies had participants leave directly from the laboratory to start their walks (Berman et al. 2008 [56] or the participants spent the night at the location as part of a
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multiday retreat (e.g. Morita et al. 2007, [57]). It is possible the psychological benefits of walking in a forest might be negated by the 20 minute drive from NU to the Forest Preserve and the return trip.
We compared the responses of people on days when they did not walk (Control, days 15 and 29) to days when took their first walks on either the sidewalk or forest path (days 8 and 22) Figure 2. We calculated the percent change in scores (((score after – score before)/score before)*100%)) for three psychological tests (PANAS, STAI-State, and PSS) within each day. Tests of significance were conducted using fixed-effects linear regression models. All results refer to comparisons made relative to the control condition.
On days when participants did not walk (Figure 2, Days 15 and 29; Figure 3, Top) participants came to the laboratory, took the tests (pre-test) and other components of the health assessment, then left the laboratory for two hours then returned to repeat the tests (post-test). On days when participants took walks (Figure 2, days 8 and 22, Figure 3, bottom), they came to the laboratory, took the pre-test, were driven to the start site for the walk, had their cardiovascular functions measured, walked, repeated the cardiovascular measurement then returned to the laboratory to take the post-test.
2.b Results:
Mood: The Positive and Negative Affect Scale (PANAS) is an index of mood [58]. The scale contains 10 items which measure positive aspects of mood (Positive Affect, Figure 4, left) and 10 items which measure negative aspects of mood (Negative Affect, Figure 4, right). Improvement in mood is indicated by an increase in the components of Positive Affect (Figure 4, left) and a decrease in components of Negative Affect (Figure 4, right).
Over the course of a day as people went about their daily activities and did not take a walk, their mood declined, as shown by declining Positive Affect scores and increasing Negative Affect scores (Figure 4, purple bars). Taking a walk on the sidewalk dampens the decline or slightly improves mood (Figure 4, grey bars). However, when the person takes a walk in the forest, there is a significant improvement in mood as shown by the large increase in positive and decrease in negative components of the affect score (Figure 4, green bars).
Anxiety: Anxiety is an emotional state characterized by agitation and restlessness. Anxiety presents both as a “trait”, that is a chronic personality condition, and as a “state”, an acute emotional condition that can be altered in moments to hours. Here we present results measured using the “ State” assessment of the State Trait Anxiety Index (STAI-State, [59]).
!
!
Figure 4. Percent Change in PANAS scores. Walking on the forest path (green bars) improves both positive (left) and negative (right) components of mood. * indicates p<0.05; ! indicates p <0.01
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Over the course of a day as people went about their daily activities and did not take a walk, their State anxiety levels increased (Figure 5, purple bars). Walking on the sidewalk is better than not walking at all as it prevented the increase in anxiety over the course of the day (Figure 5, grey bars). However, walking on the forest path resulted in a significant decline in State anxiety levels (Figure 5, green bars).
Perceived Stress: People respond differently to potentially stressful events, thus the psychological test used to assess stress measures a person’s perception of how stressed they feel (Cohen’s Perceived Stress Scale (PSS, [60]). We measured participants’ perceptions of stress using the PSS and calculated the percent change over the course of the days when people went about their daily activities of living, walked on the sidewalk, or walked in the Forest Preserve (Figure 6). Walking on the sidewalk (grey bars) appears to increase perceived stress compared to controls whereas walking on the forest path (green bars) appears to reduce perceived stress, however these trends were not statistically significant.
2.c Conclusions and Lessons Learned: Psychological Indicators of Stress and Anxiety
Walking on the forest path, even when participants had to travel 20 minutes to and from the Forest Preserve, resulted in significant improvements in psychological state as measured by improved mood and decreased anxiety. Similarly, although not statistically significant, participants were less stressed after walking in the forest than on the sidewalk. We will continue to analyze these data by incorporating additional factors, such ethnicity, Nature-Relatedness scores, and location of childhood residence in the fixed-effects linear regression model. It is possible that these individual characteristics may further strengthen these results.
3 Connecting with Nature
3.a Rationale: One objective of the FPCC Next Century
Conservation Plan is to increase interest in conservation activities and support for the Forest Preserves among people who are not already engaged in environmental stewardship. One way the FPCC proposes to do this is by encouraging people to come spend time in the Forest Preserves through advertising about the health
Figure 5. State Anxiety. Walking on the forest path led to a significant reduction in State anxiety relative to the control condition. The apparent reduction in State anxiety resulting from walking on the sidewalk did not reach statistical significance. @ indicates p = 0.06; ! indicates p <0.01.
Figure 6. Percent change in Perceived Stress Scale scores. The observed trends were not statistically significant.
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benefits of nature.
To determine if getting people to walk in nature for their health, with no additional environmental education component, would increase their concern about nature, and potentially their engagement with conservation activities, we measured the participants’ “nature connectedness” using the Nature-Relatedness 6 scale. Nature relatedness describes the way individuals view their relationship with the natural world [61]. The NR-6 is a six question scale that assesses a person’s connectedness to nature in two domains: self – the extent to which a person feels connected to nature, and perspective – the extent to which the person expresses pro-nature conservation attitudes [61]. We asked participants to complete the Nature Relatedness 6 scale once a week (days 1, 8, 15, 22, and 29) throughout the study (Figure 1 and Table 1).
A second reason for measuring participants’ nature connectedness was to determine whether the extent to which a person feels connected to nature moderates a person’s psychological and physiological responses to nature. To examine this question, the NR-6 score will be entered as a co-variate in analyses of the psychological and physiological responses to nature. The results of that analysis will be presented in a future report.
3.b Results: Each of the six questions on the NR-6 scale is rated using a 5 point Likert scale (1 =
disagree, 5 = strongly agree). The sum of the responses for all questions is averaged; higher scores represent stronger nature connectedness. We found considerable variation among individuals in their initial (Day 1) NR-6 scores (Range: 1-4.8. Mean + standard deviation (STD) = 3.5 + 0.9). Participants with Day 1 scores greater than 4 were removed from further analysis because these scores were near the maximum score of 5 for the scale and leaving little room for improvement.
To determine if walking on the forest path increased a person’s connection to nature we calculated the percent change in score ((Day8 or 22-Day15 or 29)/Day8 or 22)* 100%). Walking on the forest path led to significant improvement in NR-6 scores (Figure 7).
3.c Conclusions and Lessons Learned: Connecting with nature
These results suggest that spending time walking in nature is sufficient to increase a person’s connectedness to nature. These results are consistent with those of Lumber et al. [62] who found that people’s connections to nature are mediated by contact with nature, emotion, meaning, and compassion, and not by knowledge-based activities (i.e., learning about ecological principles or identifying species).
The present results indicate that continued efforts to get people to walk in the Forest Preserves will increase their connectedness to nature. Future studies will be needed to determine if taking walks translates into conservation advocacy and engagement.
Figure 7. Percent change in NR-6 score. NR-6 scores increased significantly after completing a series of walks on the forest path. N = 29 per group Means + standard deviations shown. * indicates p < 0.05.
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4. Anthropometrics
4.a Rationale: The purpose of this part of the study was to evaluate the logistics of incorporating
anthropometrics, the measurement of the size and proportions of the human body, in a study that required participants to undergo multiple rounds of measurements. Our long-term research goal for is to evaluate whether walking in the forest results in more rapid weight loss, improvement in body fat distribution, and a reduction in fasting blood glucose levels (a marker of diabetes) than exercising in a built environment such a study would require following subjects for up to 12 weeks. Thus we wanted to work out the feasibility of taking multiple measurements and managing the data resulting from those measurements.
Anthropometrics provides insight into the relative proportion of the body composed of lean (muscle and bone) and fat tissue. Anthropometrics also inform us about the distribution of body fat on the body. The distribution of fat is a more important indicator of health risk factors than is the percentage of fat that makes up a person’s total body weight. People who carry more fat around their waists and upper body are at higher risk metabolic and cardiovascular diseases than people who carry more of their fat in the lower body [63].
4.b. Results: Body weight and percent body fat were measured using a Tanita Bioimpedence Body
Composition Analyzer. Men were significantly heavier than women (75.1 kg vs. 57.7 kg. F = 13.07, p = 0.001). The men had significantly less body fat than women (17.5% vs. 24.3%. F = 6.39, p = 0.017). Waist-to-hip ratio was calculated from measurements made using a tape measure placed at the level of the navel to measure the waist and hip measurements made at the widest area of the buttocks [64]. As expected, men had significantly larger waist to hip ratio than women (0.83 vs.0.76; F = 18.14, p < 0.001). There were no changes in body weight, composition, or fat distribution in response to walking in either location. Changes were not expected in this healthy population.
We also estimated body fat from skin fold thicknesses measured using calipers following standard anthropometric procedures [65]. We compared the values calculated using skin fold thicknesses to those measured by bioimpedence. The correlation between the two methods was poor.
4.c. Conclusions and Lessons Learned: Anthropometrics
As a result of conducting this study we have developed an efficient procedure for storing data in Microsoft Access, implemented the necessary equations to calculate appropriate variables in the database, and run the appropriate statistical tests.
We recommend that future studies use bioimpedence rather than skinfold thickness to estimate body fat for the following reasons:
1. Variability in skinfold measurements resulting from measurements being taken by multiple investigators makes the measurements less reliable.
2. The process of taking the skinfold measurements requires participants to remove clothing which some participants find uncomfortable.
Because bioimpedence measurements are influenced by hydration, participants should be encouraged to drink at least 500 ml (2 cups) of water prior to arriving at the laboratory.
5. Biomarkers of Physiological Change
5.a Rationale: As with anthropometrics, the purpose of this part of the study was to evaluate the logistics of incorporating multiple measures of physiological health in a study that required participants
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to undergo multiple rounds of measurements. Thus we wanted to work out the feasibility of taking multiple measurements and managing the data resulting from those measurements. The biomarkers measured are considered to indicate risk of metabolic and cardiovascular disease.
5.b Results
Blood pressure Blood pressure was measured up to 4 times per day during on the various days (Table 1). In this document we report the measurements made immediately before and after the first walk in each location (days 8 and 22, Figure 2). As expected, men had significantly higher mean arterial pressures than women (87.9 vs 78.0 mmHg. F = 10.20, p = 0.003)). Walking did not lead to a change in mean arterial blood pressure. Similar results were found for systolic blood pressure and diastolic blood pressure.
Heart rate There was no significant effect of location on change in heart rate from before the walk to after the walk (interaction between location and session: F = 0.05, p = 0.8).
Heart Rate Variability (HRV): The length of time between heart beats varies with changes input to the heart from the sympathetic (fight-flight-faint) nervous system and the parasympathetic (rest and repair) nervous system. We collected data on HRV in the laboratory, during activities of daily living, and while participants walked on the sidewalk and in the forest. Because of the improvements in mood, and reductions in anxiety and perceived stress, we hypothesize that spending time in the forest will increase HRV, a sign of greater input from the parasympathetic nervous system. These data are currently being analyzed.
Cortisol: Cortisol is a stress hormone that increases blood glucose levels and inhibits the ability of insulin reduce blood glucose levels. There is a significant diurnal rhythm in cortisol with salivary concentrations rising shortly after waking then declining throughout the day until shortly before bedtime. Exposure to chronic stress results in a flattening of this diurnal rhythm [66, 67].
The participants in this study exhibited strong diurnal rhythms in cortisol secretion (F = 101.5, p < 0.001, Figure 8). There were no significant effects of sex or walk location. We are conducting a more in depth analysis of these data using mixed-models linear regression to parse out the effects of individual’s stress and anxiety levels on their cortisol levels and whether these or other factors such as whether the person grew up in a rural or urban location influences their cortisol responses. Those results will be provided at a later date.
Future studies will examine salivary cortisol after longer series of walks. We will also collect samples from each person over three consecutive days
Figure 8. Diurnal rhythm of cortisol. Saliva samples were collected two days after completing a series of three walks on either the forest path or sidewalk. Control samples were collected on the same day of the week (i.e. Sunday), but when no walks had been taken.
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because individual variation between days may obscure trends resulting from the walk location [68].
Immune System and Inflammatory Proteins In conjunction with stress hormones such as cortisol, the immune system and the inflammatory proteins associated with it mediate the effects of stress on human health and well-being [69-71]. Blood samples were collected as dried blood spots from which we proposed to measure inflammatory proteins (e.g., cytokines, Epstein-Barr virus antibodies, and C-reactive protein). These proteins serve both as markers of immune function and inflammation [72-74]. These blood samples have not been analyzed. Because of the expense of these assays, we are waiting to see if the results of the psychological tests and other physiological indicators suggest that spending the money will be worthwhile.
Blood Glucose Fasting blood glucose (FBG) concentrations were measured before the first walk in each location and seventy-two hours after completing the third walk in each location (Table 1). Elevated fasting blood glucose levels are the clinical hallmark of diabetes. We did not expect to see a change in FBG given the short duration of the study (3 walks in one week for each location) and the fact that we recruited a healthy people, we did not screen for symptoms of pre-diabetes (FBG 100-125 mg/dl) or diabetes (FBG greater than 140 mg/dl).
Much to our surprise, several of the participants in this study had FBG concentrations indicative of pre-diabetes and boarding on diabetes (Figure 9, purple bars). The results suggest that walking in the forest resulted in a reduction of fasting blood glucose that persisted for 72 hours after the final walk. Although there are no statistically significant differences in fasting blood glucose levels, there was a slight decline in the average FBG 72 hours after completing the series of walks on the forest path (Figure 9, Forest/Before and After) which was not observed when people walked on the sidewalk (Figure 9, Sidewalk/Before and After). When the percent change in FBG was calculated for each person ((After-Before)/Before*100%) the trend was for an increase in FBG after walking on the sidewalk (Figure 10, grey bars), but a decrease after walking on the forest path (Figure 10, green bars).
Future studies will be designed to recruit people with pre-diabetic blood glucose levels. The protocol will be modified to follow participants for a total of 12 weeks, with measurements at monthly intervals to assess changes in fasting blood glucose and anthropometric measures.
Figure 9. Fasting blood glucose before the first walk (Before) or 72 hours after the third walk (After) in each location. Individual values; darker circles = mean. .
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5.c Conclusions and Lessons Learned: Biomarkers of Physiological Change
As with the data collected for anthropometric measures, the primary result of conducting this study has been to work out the logistics of collecting the needed samples and developing the data management procedures required to handle the large amount of data resulting from the study.
We found no differences in heart rate or blood pressure as a function of whether participants walked on either the sidewalk or forest preserve path. Other studies that report changes in heart rate or blood pressure differed significantly in their procedures from this study [75-80]. Understanding the influence of differences in procedure will be important to establishing best practices for developing NRx.
The biggest surprise from this part of the study was the observation of a persistent decline in blood glucose levels after completing a series of three walks on the forest path. These data are encouraging and suggest that further studies focused on participants with a diagnosis of pre-diabetes (fasting blood glucose levels between 100-120 mg/dl) is warranted. These data alone provide an important reason for people to walk in the woods.
Summary The purpose of this project was to advance Goal 2 of the NCCP (People). Specifically, this project aimed to provide data essential to the development of nature prescriptions (NRx) to be used to encourage people to get outdoors. This is one of the first data sets from a controlled, statistically well-powered longitudinal study which compares the psychological and physiological benefits of walking in nature as compared to walking on a suburban sidewalk and to activities of daily living.
These data demonstrate that the body of literature attesting to the physiological health benefits of nature, literature derived primarily from research on males in Japan, Korea, and Taiwan, also applies to the Forest Preserves of Chicago.
We analyzed our data looking for differences between males and females and did not find significant differences between the sexes, thus the health benefits of nature accrue equally to males and females.
We learned that significant mental health benefits can be gained from taking a 50 minute walk on a Forest Preserve trail. Most importantly for residents of Cook County, these benefits are maintained even when a person spends 20 minutes driving each way to and from a Forest Preserve.
We learned that taking a series of three 50-minute walks on a Forest Preserve trail leads to a significant increase in a person’s sense of connectedness to nature.
Figure 10. Fasting blood glucose levels reanalyzed as percent change for each individual before the first walk and 72 hours after the 3rd walk in each location. Mean + standard error.
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Finally, we observed that people who started the study with fasting blood glucose levels in the range that would be consider to reflect pre-diabetes showed a reduction in their blood glucose levels after completing a series of three 50-minute walks on the Forest Preserve trail.
Future directions
In the future, we wish to expand this research to examine the effects of longer periods of activity (e.g., 6 to 12 weeks) to capture data on health outcomes resulting from sustained activity and exposure to nature. We also wish to expand the studies to include individuals with existing health risk factors, such as obesity or diabetes (both Type 1 and Type 2). Documenting the benefits of walking in nature to individuals with specific health concerns will provide the evidence necessary to develop practices, programs and policies for the use of nature prescriptions in community and public health programs. The data collected in current study will be used to support applications to federal agencies (i.e. the National Institutes of Health) and non-profit organizations for funding for future studies. We will also use these data in presentations to physicians and other health-care providers to encourage them to adopt NRx in their practices.
Presentations Made and Meeting Abstracts Submitted
Horton T.H., Berman M.G., Cetrone H., Koselka E., Lee A.J., Leonard W.R., Norman G.J., and Smith K.E.L. Walking Green: Developing an Evidence Base for Nature Prescriptions. Natural Capital Symposium. Stanford University. Palo Alto, CA. 20-23 March 2017. http://www.naturalcapitalproject.org/natcap2017/
Horton, T.H., Where’s the Tree? Identifying the Effects of Nature. Keynote address to the Dupage Environmental Summit. The Conservation Foundation. Northern Illinois University, Naperville, IL 25 January 2018. Video of presentation: https://www.youtube.com/watch?v=W2kBaXt22LM&feature=youtu.be
Koselka, E., Lee, A., Cetrone, H., Minasov, A., Leonard, W.R., and Horton, T.H. Testing the Biophilia Hypothesis: effects of walking in forested versus built environments on stress and anxiety. Annual Meeting of the Human Biology Association. Austin, TX. 11-12 April, 2018.
Horton, T.H., Koselka, E.P.D., Lee, A.J., Cetrone, H.M., Minasov, A., Leonard, W.R., Pereira, M.A., Nogueira De Brito, J., Larson, J.M. Schneider, I.S. Lessons Learned: Implementation of longitudinal studies of green exercise. International Congress on Integrative Medicine & Health. Baltimore, MD. 8-11 May, 2018.
Additional Funding Sources
The Negaunee Foundation (to T.H. Horton), The TCF Foundation (to M.G. Berman), Weinberg College of Arts and Sciences, Northwestern University (to William R. Leonard)
Acknowledgements
This work would not have been possible without the support and assistance of Hollyn M. Cetrone, Elizabeth Koselka, Annie J. Lee, and Arseniy Minasov. Their assistance with collecting, managing, and analyzing data was invaluable. The support and encouragement of my colleagues, especially the past and current chairpersons of the Department of Anthropology, Drs. William Leonard and Matthew Johnson, as I undertook this new research project has also been essentially.
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