Association between Contact with Nature and Anxiety, Stress and Depression Symptoms: A Primary Survey in Brazil

Abstract

Mental health benefits have been linked to human interaction with nature. However, most studies have been carried out in developed countries, limiting the generalizability of empirical findings to other parts of the world. To address this gap, this study was conducted in Brazil. The objective of the study was to assess whether the frequency of contact with nature affects the occurrence of anxiety, stress, and depression. Data were collected between June and July 2022 through an online survey (n = 1186, 1 − α = 0.95, p = 0.05, 1 − β = 0.85, rho = 0.1). Thus, the public online survey made it possible to carry out voluntary response sampling suitable for an exploratory study, with the purpose of an initial understanding of an under-researched population. First, a logistic regression was performed for quantifying the association between contact with nature and mental symptoms. In addition, three groups of people having different frequencies (low, medium, and high) of contact with nature and a reference group, comprised of those who reported no contact, were compared using Kruskal–Wallis and Dwass–Steel–Chritchlow–Fligner tests. This study employs a cross-sectional design and relies on retrospective recall. As a result, the research hypothesis was confirmed. People who very rarely have contact with nature had a 97.95% probability of moderate occurrence of stress, which decreases to 20.98% for people who have contact with nature frequently. Furthermore, in the same comparison, the probability of occurrence was 3.6 times lower for anxiety and 4.8 times lower for depression. In conclusion, the evidence indicates that the greater the frequency of contact with nature, the lower the occurrence of stress, anxiety, and depression symptoms. Nevertheless, the benefits of this contact were significant only when its frequency was moderate (about once or twice a week) or higher.

1. Introduction

Humankind has undergone great transformations, with several impacts on its habitat and lifestyle. Early civilizations lived as nomads in direct contact with nature, but the emergence of agriculture allowed the growth of cities, and the increase in built-up environments and respective suppression of natural areas has intensified in the most recent period of human history [1]. Humankind’s distance from the adversities of the natural environment has brought benefits in many fields, such as sanitation, transport, and medicine. On the other hand, modern society’s increasing focus on the built environment and designed entertainment, such as social networks in digital medias, has raised concerns about higher rates of mental health problems associated with the fact that people spend less time in contact with nature [2,3,4,5,6,7].

Among the studies that seek to explain the process by which contact with nature brings benefits to human health, Kellert [8] analyzed the biophilia hypothesis developed by Wilson [9]. According to this thesis, survival of humankind throughout the evolutionary process was dependent on the physical, mental, and intellectual improvement developed from the direct relationship with nature. Thus, humankind’s ancestors would have perpetuated an attraction, biologically encoded, to the natural environment [10].

According to McMahan and Estes [11], the fact that humankind’s ancestors lived amid nature, taking advantage of the availability of resources such as water and food, would have produced a beneficial association that contributes to well-being and quality of life. The mental health benefits of contact with nature have also been linked to its effect on the right hemisphere of the brain and the parasympathetic nervous system, which contributes to the restoration of physical energy, to calm excess brain activity after stressful events [12].

From the perspective of Attention Restoration Theory (ART) [13,14,15], nature acts on the improvement of mental fatigue and, in this way, contributes to the recovery of associated mental health problems. According to ART, mental fatigue is related to voluntary attention (concentration), which tends to increase over time. Contact with nature activates involuntary attention (distraction), which does not require effort, allowing rest and restoration of brain functioning.

As pointed out by Owens and Bunce [16], p. 2, “the idea that contact with nature is positive for human health is not new”. Several studies have revealed evidence on the effects of contact with nature in different dimensions of human health [17]. Reductions in stress, anxiety, and depression symptoms are among the mental health benefits studied over the years [8,18,19,20,21,22,23,24,25,26,27].

Notwithstanding, most studies have been carried out in developed countries, thus limiting the generalizability of empirical findings to other parts of the [28]. Responding to ongoing calls for more studies in developing countries [29], especially in Latin America, where there is a dearth of primary research [7], this study was conducted in Brazil. The objective was to evaluate the research hypothesis that the frequency of contact with nature affects the occurrence of anxiety, stress, and depression symptoms.

2. Method

Initially, data collection was performed by the application of an online survey between June and July 2022. This process is according to Brazil’s ethical requirements for studies involving human beings (Process #58149622.3.0000.0077). As inclusion criteria, we considered participants who are at least 18 years old and resident in Brazil. There are no further distinctions such as gender, region, social strata, education level, etc. The sample size of 1186 respondents provided a test power (1 − β) of 0.85 for a significance level (α) of 0.05 and a minimum detectable effect size (rho) of 0.1. The effect size observed in the study was calculated from the variances, using Pearson’s test.

Thus, the public online survey enabled voluntary response sampling suitable for an exploratory study, with the purpose of an initial understanding of an under-researched population. Filling out an online self-report, respondents were asked about the occurrence of anxiety, stress, and depression symptoms in the last month, considering [30]: (i) stress symptoms: nervousness, overreaction, agitation, intolerance, feeling very sensitive; (ii) anxiety symptoms: fatigue, wheezing, shakiness, racing thoughts, increased heart rate; and (iii) depression symptoms: sadness, negative thoughts, hopelessness, discouragement, low self-esteem. The symptoms were scored using a discrete six-point scale: 1, very rarely (less than once a month); 2, rarely (about once a month); 3, sometimes (about twice a month); 4, moderately (about once a week); 5, frequently (about twice a week); and 6, very often (more than twice a week). It is worth mentioning that only symptoms based on the Depression, Anxiety, and Stress Scale (DASS) were used as a reference, to support the respondents in the retrospective recall of such symptoms. Therefore, as the purpose of the study was to measure the frequency of this occurrence, without classifying the severity of symptoms, cut-offs and any other psychometric properties of the DASS were not used.

In the second question, respondents stated the frequency with which they usually have contact with nature, considering: (i) nature: natural areas, such as gardens, forests, grassland, reserves, woods, parks, beaches, mountains, or similar environments; and (ii) contact with nature: recreational or leisure activity in natural areas, such as contemplating, walking, running, cycling, horseback riding, camping, fishing, swimming, surfing, meditating, or similar activities.

This study employs a cross-sectional design and relies on retrospective recall. For the comparative analysis, four groups of respondents were formed, according to the frequency of nature contact: reference group (G0), hardly ever (less than once a month); low frequency group (G1), sometimes (about once or twice a month); medium frequency group (G2), moderately (about once or twice a week); and high frequency group (G3), frequently (more than twice a week). Aiming to verify the reliability of this scale of grouping, the Cronbach’s alpha was calculated, which resulted in 0.736, indicating an acceptable internal consistency.

As the data collected are not continuous, a non-parametric approach was used for statistical analysis. First, we performed a logistic regression analysis aimed at quantifying the association between events: (e₁) contact with nature; and (e₂) occurrence of anxiety, stress, and depression symptoms. If p < 0.05 in the regression, and the odds ratio (OR) is < 1 (95% CI), then the events are negatively associated [31]. In this case, the presence of event e₁ (contact with nature) reduces the chances of event e₂ (occurrence of symptoms).

Once the hypothesis of dependence between events has been verified, the responses given by the groups (G0, G1, G2, and G3) were compared using two-sided Kruskal–Wallis and Dwass–Steel–Chritchlow–Fligner (DSCF) tests. All analyses considered a confidence level (1 − α) of 95%.

Whereas stress, anxiety, and depression problems can lead to reduced contact with nature, there may well be bi-directional effects, so a review of the current literature was undertaken, identifying which studies are longitudinal and which are cross-sectional, to help towards disentangling the direction of causality. To search for the most reliable, relevant, and up-to-date literature, we use the Scopus database, in which the following query was applied: title-abs-key (“nature” and (“green” or “contact” or “disorder” or “depression” or “anxiety”) and (“longitudinal” or “transversal” or “cross-sectional”)) and (limit-to (pubstage, “final”)) and (limit-to (doctype, “ar”)) and (limit-to (subjarea, “psyc”) or limit-to (subjarea, “envi”)) and (limit-to (pubyear, 2023) or limit-to (pubyear, 2022) or limit-to (pubyear, 2021) or limit-to (pubyear, 2020) or limit-to (pubyear, 2019) or limit-to (pubyear, 2018) or limit-to (pubyear, 2017) or limit-to (pubyear, 2016) or limit-to (pubyear, 2015) or limit-to (pubyear, 2014) or limit-to (pubyear, 2013) or limit-to (pubyear, 2012)) and (limit-to (language, “English”)). Considering the publications of the last 10 years (from 2012), the 200 most recent articles were preliminarily screened. After excluding those outside the scope, only 20.6% used longitudinal designs, with results that were compared to those of the present study.

3. Results

Considering the cases with goodness-of-fit of the data to the model and a significant regression coefficient (δ), the OR was <1 for all associations under analysis (

Table 1. Association between frequency of contact with nature and occurrence of stress, anxiety, and depression symptoms.

	Event	p		OR (95% CI)	Likelihood of Occurrence (%)
		GoF	δ		$\mathbf{G}0 \left({\mathit{e}}_1^1\right)$	$\mathbf{G}1 \left({\mathit{e}}_1^2\right)$	$\mathbf{G}2 \left({\mathit{e}}_1^3\right)$	$\mathbf{G}3 \left({\mathit{e}}_1^4\right)$
Stress	($e_2^1$)	<0.001	<0.001	0.638	75.99	66.90	56.34	45.17
	($e_2^2$)	<0.001	<0.001	0.177	97.95	89.45	60.00	20.98
	($e_2^3$)	0.043	0.038	0.635	26.28	18.88	12.88	8.58
Anxiety	($e_2^1$)	0.214	0.216	*	*	*	*	*
	($e_2^2$)	<0.001	<0.001	0.258	95.51	84.60	58.64	26.80
	($e_2^3$)	0.001	<0.001	0.424	46.64	27.04	13.58	6.25
Depression	($e_2^1$)	0.038	0.037	0.764	36.63	30.63	25.23	20.49
	($e_2^2$)	<0.001	<0.001	0.510	41.75	26.78	15.73	8.70
	($e_2^3$)	0.001	0.0082	0.586	20.66	13.23	8.20	4.97

G0: reference group; G1: low frequency group; G2: medium frequency group; G3: high frequency group; $e_2^1$: sometimes; $e_2^2$: moderately; $e_2^3$: frequently; OR: odds ratio; GoF: goodness-of-fit (χ²); δ: regression coefficient; * non-adequacy of adjustment of the data to the model or non-significant regression.

). This finding indicates that the likelihood of occurrence of the symptoms (anxiety, stress, and depression) tends to decrease when the frequency of nature contact increases, corroborating the research hypothesis.

Participants who very rarely have contact with nature (G0) have a 97.95% probability of moderate occurrence of stress ($e_2^2$). This probability decreases to 20.98% for people who have contact with nature frequently (G3), which is 4.7 times lower. For the same comparison (i.e., considering a moderate occurrence of the symptoms for both G0 and G3), the probability of occurrence was 3.6 times lower for anxiety (from 95.5% in G0 to 26.8% in G3) and 4.8 times lower for depression (from 41.75% to 8.7%). As can be seen in

Table 2. Significance of frequency of contact with nature on the occurrence of anxiety, stress, and depression symptoms.

	Kruskal–Wallis *	DSCF *
		G0 × G1	G0 × G2	G0 × G3
Stress	<0.001	0.197	<0.001	<0.001
Anxiety	<0.001	0.607	0.001	<0.001
Depression	<0.001	0.070	<0.001	<0.001

* p value: probability of rejecting the null hypothesis (H0: the frequency of contact with nature does not affect the occurrence of anxiety, stress, and depression symptoms) when it is true.

, the null hypothesis can be rejected at a confidence level of 99.9% (p ≤ 0.001) for almost all multiple paired comparisons, except in the comparison between G0 and G1.

In other words, the research hypothesis that the frequency of contact with nature affects the occurrence of anxiety, stress, and depression symptoms was confirmed. The effect size observed in the study was 0.230 for anxiety, 0.203 for stress, and 0.196 for depression, considered as a medium-sized effect. However, it is important to highlight that there was no statistically significant effect (p > 0.05) on the occurrence of symptoms when the frequency of contact with nature was only sometimes, that is, about once or twice a month (G0 × G1). Therefore, the benefits of this contact were significant only when its frequency was moderate (about once or twice a week) or higher.

4. Discussion

4.1. Effects on Anxiety, Stress, and Depression Symptoms

In agreement with our results, previous studies have also verified that contact with nature, which includes environments, such as forests, being near trees (or other vegetation) and water features (such as rivers and lakes), grassland, reserves, woods, or parks, had positive impacts on stress, anxiety, and depression.

Ulrich et al. [18] analyzed the effects of natural and urban settings on people who had been subjected to a stressful condition (watching a horror movie). Based on physiological measures such as heart rate and muscle tension, the authors verified that the stress recovery time was shorter when people were exposed to natural rather than urban environments.

Parsons et al. [19] evaluated stress recovery in drivers who had traveled one of the following four routes: forest/rural scenery, outside golf courses, urban scenes, and mixed scenarios. The results showed that drivers on routes dominated by natural scenes experienced faster recovery from stress than participants who saw environments dominated by artificial scenes (buildings) while driving.

Cox et al. [32] found that residents of rural areas, with higher “doses of nature”, had better mental health (measured on scales of depression, anxiety, and stress) than people who live in urban areas characterized by predominantly built environments. Similarly, other studies, such as Fan et al. [23], Beyer et al. [24], Rautio et al. [26], and Barreto et al. [27], have shown an inverse association between the presence of green areas around the home and the occurrence of more common mental health problems such as anxiety and depression.

Mackay and Neil [22] related physical exercise in natural areas with a considerable decrease in anxiety levels. Song et al. [25] compared the effect of physical activities in natural (greener) and artificial (more built) environments. The authors verified a more significant decrease in anxiety and stress levels in people who walk in natural areas, such as parks, compared to people who walk on urban roads (artificial, built, or designed areas). Pretty et al. [20] found that those who walked daily around a natural park, with woods and lakes, experienced significantly less depression than people who walked in a shopping mall.

Regarding the mechanisms involved in explaining the association between contact with nature and the mental health benefits, Owens and Bunce [16] argue that there are several potential candidates. Among them, the authors highlight mechanisms related to stress, rumination (repetitive thinking), mindfulness, sleep, and exercise (physical activity). Some evidence supports that contact with nature is capable of mitigating cortisol hypersecretion and, consequently, of reducing stress, which is also a risk factor for depression [33,34].

Studies have also found that walking in nature and forest bathing [35] were able to reduce the frequency of repetitive negative thoughts (rumination), contributing positively to the improvement of depression and anxiety symptoms [36,37,38,39].

Meta-analyses have confirmed evidence that mindfulness practice provides a non-judgmental level of awareness, which is heightened when performed in contact with nature, becoming even more beneficial for mental health, in terms of a reduction in stress, anxiety, and depression [40,41,42,43,44].

Upon performing a literature review, Shin et al. [45] reported a positive association between green walking and better night-time indices of autonomic nervous system functioning. Thus, by contributing to good sleep, contact with nature can also mitigate the deleterious effects of poor sleep on mood and well-being [46].

By improving emotional regulation [47] and self-esteem [48] and reducing obesity [49] and inflammatory processes [50], exercise (physical activity) has been shown by several studies to be beneficial for mental health, especially under conditions of exposure to nature, and be more beneficial than engaging in similar activities in a non-forested urban area [29,51,52].

Whereas it is entirely possible for the hypothetical direction to be reversed, that is, mental problems may lead to reduced contact with nature, to help towards disentangling the direction of causality, the results of recent studies with longitudinal designs are highlighted below, corroborating the results of the present study.

Das and Gailey [53] longitudinally assessed whether physical activities (walking or running) in contact with nature (green exercise) provided a decline in adverse mental health symptoms (anxiety and depression) during the COVID-19 pandemic lockdown. The authors found fewer adverse symptoms due to green exercise. Moreover, they found that green exercise, as opposed to indoor exercise, corresponds with a decrease in anxiety and depression symptoms.

Yang et al. [54] performed a multilevel analysis to determine the longitudinal effects of therapeutic gardening on mental health and well-being during the COVID-19 pandemic. The results showed that mental health improved significantly over time as the therapeutic gardening program progressed. The authors concluded that therapeutic gardening is a promising nature-based intervention for improving mental health.

Klein et al. [55] investigated associations between residential green space and mental health, including depression, through a longitudinal survey. Their conclusion was that residing amid greater green spaces was associated with lower levels of depressive symptoms.

Colléony et al. [56] conducted a longitudinal study to quantify the effects of nature deprivations on health and well-being. The results confirmed that the frequency, duration, and quality of contact with nature dropped during the COVID-19 pandemic lockdown, particularly for people living in less green neighborhoods, where a significant decrease in well-being was also found.

Perrins et al. [57] developed a longitudinal survey to assess whether the presence of natural elements in workers’ day-to-day environments can improve workers’ psychological well-being. The authors found that contact with nature in everyday life is significantly associated with decreased level of anxiety.

Maes et al. [58] used longitudinal data to examine associations between types of the natural environment and adolescent mental health. The study showed that greater daily exposure to forest areas, but not pastures, was associated with a lower risk of emotional problems.

Olszewska-Guizzo et al. [59] investigated longitudinal changes in depressed mood from before COVID-19 to immediately after the national lockdown in Singapore ended. The results showed that greater exposure to nature during the lockdown did not help mitigate depressive symptoms, as previous research suggests. The authors argue that this may be due to the lower quality of exposure to nature during the lockdown.

As a practical implication, recognition of the benefits of contact with nature has become increasingly relevant in healthcare (nature-based therapeutics). Although such an implication is not the focus of this study, a brief summary is presented here.

4.2. Nature-Based Therapeutics

Nature-based therapies seek to provide health benefits through interactions with plants, animals, and natural landscapes: for example, therapeutic horticulture [60], adventure therapy [61], wilderness therapy [62,63], green exercise [64], and forest bathing [65].

Hechter and Fife [66] point out that therapies based on contact with nature have helped patients to face fears and insecurities, with significant improvements in anxiety. Brown and Grant [67] found that therapies based on a high level of interaction with nature provide several benefits to groups of psychiatric patients, especially those with chemical dependency.

Greenleaf et al. [64] found that green exercise was able to reduce the deterioration of mental abilities in patients with Alzheimer’s disease. Similarly, McCaffrey [68] assessed that walking in garden areas, such as urban parks, had a positive effect on older adults diagnosed with mild to moderate depression. Detweiler et al. [69] evaluated the effect of walking in a garden in a psychiatric facility on the behavior of patients with dementia. The authors found that residents who used the garden more frequently started to have less agitated behavior and an improvement in mood and quality of life.

The use of plants through horticulture has also been promising in treating people with dementia. Son et al. [60] found that therapeutic horticulture was beneficial for the self-esteem and sociability of patients with progressive neurodegeneration. Gigliotti and Jarrott [70] found that horticultural activities carried out once a week for just half an hour favored higher levels of engagement and affection among psychiatric patients. Kam and Siu [71] investigated the effect of horticulture on people with psychiatric illnesses. The study found that horticulture was effective in reducing levels of anxiety, depression, and stress among participants in the pilot study. Wichrowski et al. [72] evaluated the effects of horticulture on mood and heart rate in patients on a cardiac rehabilitation program. The results indicated an improvement in the mood state, which is beneficial for reducing stress. To the extent that stress contributes to coronary heart disease, it was concluded that horticulture is an effective therapy for cardiac rehabilitation.

Exposure to nature based on adventure therapy can lead to changes in the cognitive-behavioral pattern of adolescents with obesity, and Jelalian et al. [61] found that there was a significant difference in the percentage of participants who maintained minimal weight loss, concluding that this type of therapy is a promising strategy, especially in older adolescents.

Wilderness therapy has shown promise in improving delinquent behavior; Wilson and Lipsey [73] evaluated that it had a positive impact on the behavior of young people, reducing antisocial behavior and the carrying out of crimes. Russell [62] also noted the effectiveness of wilderness therapy in reducing behavioral and emotional problems in adolescents. Furthermore, the effectiveness of wilderness therapy as a form of rehabilitation for individuals with schizophrenia was assessed by Voruganti et al. [63], with patients showing improvement in cognitive skills and self-esteem, in addition to significant weight loss, along with relevant occupational and social gains.

5. Conclusions

The present study evaluated the association between interaction with nature and the hypothetical reduction in stress, anxiety, and depression symptoms through primary research in Brazil. The research hypothesis was confirmed and evidence indicates that the greater the frequency of contact with nature, the lower the occurrence of symptoms (from 3.6 to 4.8 times lower). Nevertheless, the benefits of this contact were significant only when its frequency was moderate (about once or twice a week) or higher.

With regard to limitations, the research did not take into account influencing factors associated with the form of contact (contemplating, walking, running, etc.) or the type of nature (gardens, forests, woods, parks, etc.). Moreover, in order to contribute to an initial understanding of an under-researched population, the influence of potential confounding factors (age, gender, income, education, etc.) was not considered. Other limitations of this study are that it is cross-sectional, it relies on retrospective recall, and there are no randomized components. Considering that the vast majority of studies have used cross-sectional designs, another recommendation for future studies is to employ longitudinal designs and assess how other factors affect the health benefits of contact with nature.