Nature-Based Interventions Targeting Elderly People’s Health and Well-Being: An Evidence Map
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1. Introduction
Population aging is a recent global phenomenon, which has only been achieved due to advances in medical sciences and healthcare over the past two centuries, as well as the general improvement in living and working conditions, with significant demographic, biological, social, economic, and behavioral transformations [1]. With unprecedented numbers in human history, there is a transition in the demographic structure of the European Union, which in 2020 had 20.6% of the population being over 65 years old, with a projected increase to 29.5% in 2050 [2]. Specifically in Portugal, also in 2020, the number of older people corresponded to 22.4% of the country’s population [3]. Between 2011 and 2019, there was a reduction in the rate of live births, accompanied by an increase in the fertility rate. However, this increase was insufficient to ensure the replacement of generations. According to demographic projections, Portugal is expected to experience a population decline by 2080, decreasing from 10.3 million residents in 2019 to 8.2 million. At the national level, projections indicate a decrease in the proportion of young people in the total population and an increase in the proportion of individuals aged 65 or over. This shift is projected to result in an almost doubling of the aging rate [4]. In Brazil, although it is known as a “young country”, there is an inversion of the age pyramid, characterized by a significant increase in the elderly population. There has been a significant increase in life expectancy, which was 76.3 years in 2018 and is expected to reach 81.3 years in 2050 [5]. This increase directly impacts the absolute number of older adults in the Brazilian population.
In 2010, the number of people over 60 years of age was 14.2 million, with projections of 41.5 million in 2030 and 73.5 million in 2060, so that in 2025, Brazil should be the sixth ranking country in the world in terms of elderly population [5]. Such changes in the age structure of the population result in a continued and strong demographic aging, emphasizing the need to create and strengthen public policies that are aimed at promoting active and healthy aging. This involves not only the absence of diseases but also the preservation of functional capacity and the maintenance of well-being and quality of life [6].
According to the World Health Organization (WHO), elements such as access to economic resources, levels of education, physical and social environment, working conditions, access to healthcare services, and individual behaviors are considered key determinants of health. They constitute a complex set of factors that directly influence the health status of populations. Understanding these determinants is crucial for developing effective public policies aimed at improving the health of populations, especially the elderly, whose aging process involves multifactorial elements. Therefore, integrating these determinants into public health programs and policies addresses immediate health needs and establishes structures to address the root causes of diseases. The aim is comprehensive health promotion, targeting not just disease absence but physical, mental, and social well-being [7].
In Brazil and globally, there are legislations and recommendations that are aimed at strengthening such public policies. For instance, Brazilian Federal Law No. 10741 of 1 October 2003 asserts that it is the duty of the State and society to preserve the physical and mental health of older adults [8]. Additionally, the World Health Organization’s document, “Global Strategy and Action Plan on Aging and Health” outlines global strategies to support healthy aging [9]. As part of global initiatives, the known factors contributing to healthy aging and maintaining a quality of life include regular physical exercise, a balanced diet, pleasant social interactions between family and friends, regular sleep, full exercise of autonomy, periodic check-ups, activities that promote a sense of well-being, and stress reduction [10,11].
In this context, nature-based interventions are already pointed out as sources of several health benefits for the general population, with particular relevance for the well-being of the elderly. These benefits include the improvement of mental health, with a reduction in stress, anxiety, and depression [12]; positive effects on mood [13]; the reduction in blood pressure levels in hypertensive patients [14]; the improvement of interpersonal relationships [15]; the restoration of attention and memory [16]; the improvement of the immune system [17]; and the management of chronic pain [18]. Additionally, the known influence of contact with nature on mental health, coupled with its economic impact on public coffers, is noteworthy. In Australia, the mental health benefits derived from regular visits to natural areas alone generate the relevant savings of USD 6 trillion annually. On the other hand, if the population does not have the opportunity to visit parks and natural areas, the increase in mental health treatment costs can rise from 10% to 17.5% of the Gross Domestic Product [19].
Therefore, sustaining activities that foster a consistent human–nature relationship is not only directly linked to health promotion but also has indirect economic implications. This reinforces the necessity of expanding knowledge and actions on this topic in order to influence macro-level management that recognizes the environments that are essential for the well-being of the elderly and promotes healthy aging.
Another niche that can benefit from deepening our knowledge on the impact of nature-based interventions on the health of older people is tourism. In Europe, viewing tourism in natural areas as a tool for active aging presents an opportunity for the social and economic development of large areas, where the preservation of the environment is also a source of health and well-being [20].
However, sectors such as health, economics, and social well-being, which stand to benefit from the incorporation of nature as a tool for promoting healthy aging, currently lack sufficient scientific evidence on the topic. Existing literature on Nature and Health in the context of aging focuses on pre-existing conditions and the benefits of nature contact as an indirect form of treatment, often associated with pharmacological, procedural, or interventional treatment [21,22,23].
Nature-based interventions refer to numerous care modalities, such as forest bathing, forest therapy, therapeutic gardens, and other activities that are developed in natural settings. This diversity poses challenges for decision making, both for health professionals tasked with selecting the most effective interventions for older adults and stakeholders making investment decisions related to natural areas that are targeted at this public (in terms of infrastructure and tourism). Additionally, formulating appropriate public policies that effectively integrate natural environments with healthcare presents a complex challenge.
Despite the recognition that individuals, irrespective of their surroundings (urban, peri-urban, rural), gain greater health and well-being benefits from contact with biodiverse and perceived natural areas [24], we still face a lack of comprehensive elements to systematize actions targeting the elderly across diverse contexts.
Thus, considering the growing demand for advancing the implementation of nature-based interventions promoting the health and well-being of the elderly, we present an evidence map facilitating access to information and scientific evidence in health within this domain. In both clinical and management contexts related to natural spaces and services, making well-informed decisions necessitates access to robust, high-quality evidence. However, not all evidence is equally convincing or reliable, and a comprehensive synthesis on the topic is currently lacking for the older population. Our evidence map aims to address this gap by identifying, describing, and organizing available evidence on nature-based interventions targeting older people. It serves as a valuable resource for informed decision making, offering researchers, managers, professionals, and students in the fields of health, natural environments, and related areas access to the best knowledge and evidence available. It should also be emphasized that an evidence map can facilitate the translation of scientific knowledge and its incorporation into the real world and point out gaps for the development of future research [25,26].
4. Discussion
The aim of this evidence map was to identify, describe, and organize the available research on nature-based interventions in older adults. With the application of the search strategy, more than 10,000 articles were identified. However, with the refinement of the search and application of the inclusion and exclusion criteria, only 12 studies were selected, pointing us to the low amount of evidence that is available on the subject.
Among the years evaluated (2012 to 2021), it is possible to see a growing trend in the number of studies published, showing that, despite the low amount of available evidence, the theme has been gaining in focus in international contexts, especially in the Northern Hemisphere, composed mostly of developed countries, without any representation of the countries of the Southern Hemisphere so far.
The evidence map was developed by crossing nature-based interventions in older adults, namely, “forest bathing”, “hiking in natural areas”, “therapeutic garden”, “virtual reality”, and “forest sound” with outcomes categorized into “Physical Aspects: Cardiovascular and Pulmonary”, “Physical Aspects: Neuro-immuno-endocrinological”, and “Mental/Behavioral Aspects”. It is an interactive, easy-to-use, and visually attractive map that summarizes the information found, also including the quality assessment of the studies.
Regarding the outcome Physical Aspects: Cardiovascular and Pulmonary, one of the notable results points to a reduction in blood pressure in four of the eleven articles analyzed. The following were cited as benefits associated with lower blood pressure: reduced heart rate, improved lung function, reduced heart failure biomarkers, reduced cardiac variation, and reduced vasoconstriction [18,32,36,37,39,40]. In the outcome Physical Aspects: Neuro-immuno-endocrinological, five studies showed positive results in reducing inflammation and activation of the immune system through plasma analysis of decreased pro-inflammatory cytokines, IL-6, IL-8, C-reactive protein, ET-1, granzyme B, tumor necrosis factor ⲁ, T lymphocytes, and NK cells [18,36,39,40,42]. The result of one study showed a reduction in biological markers of heart failure as a consequence of the attenuation of the inflammatory response and activation of antioxidant actions [40], which was also indicated in the study showing an improvement in the condition of Chronic Obstructive Disease with a gain in lung function due to an inflammatory reduction and immunological action [39]. In another study, a salivary cortisol measurement was used to assess the stress level of the elderly, and there was a reduction in the amount of cortisol after the intervention [37]. A study conducted in the Republic of Korea showed that the breathing and walking program in forest bathing brought health benefits to the elderly population in terms of neurophysiology, heart rate variability, and bioimpedance [42].
As evaluative tools used in the studies to analyze Outcomes—Mental/Behavioral Aspects, the Profile of Mood States (POMS) questionnaire, the Geriatric Depression Scale (GDS-30), Anxiety and Stress Scale (HADS), and the Perceived Stress Questionnaire (PSS) were found. The POMS was used in four studies, where reductions in the negative mood states of older adults were found [18,36,39,41].
To analyze the neuro-psychophysiological aspects, the Mini Mental State Examination, Barthel Index, and Neuropsychiatric Inventory Scale were used in one article, and improvement was found in the degree of anxiety, sleep, and quality of life in the elderly. Two articles reported an improvement in cognitive decline after an intervention in nature [34,37].
Other observed results point to reduced tension, anxiety, and fatigue [36]; increased well-being [34]; increased happiness and empathy [41]; improved negative mood states [32,40]; reduced stress [35,39]; improved sleep and quality of life [34]; and reduced depression [33,36] after the interventions.
A high heterogeneity among the articles was found on the determination of the duration of the nature-based interventions, periodicity and number of sessions, condition of the population of older people involved in the studies (healthy or unhealthy), type of nature-based intervention—with direct and indirect contact—and association of the intervention with physical activity, meditation, or breathing practices.
Regarding the duration of the interventions, they ranged from 40 min to 2 h daily (also depending on the number of weekly sessions). The literature lacks consensus regarding the ideal exposure time to nature. Two pertinent studies in the field present divergent perspectives. Researchers from the University of Exeter, United Kingdom, demonstrated that 120 min of contact with nature per week benefit physical health and psychological well-being. This study, involving nearly 20,000 individuals, recommends that two hours of exposure to natural environments, either in a single visit or through multiple brief ones, prove beneficial for diverse ethnic groups, including individuals with chronic diseases or other disabilities. The study also highlighted that proximity to natural environments near residences constituted the primary means of contact [43]. Conversely, another study from the United Kingdom suggests a shift in the paradigm from “how much time” to “how meaningful the experiences” in nature are. Therefore, it emphasizes the importance of quality moments and the appreciation of emotional interactions with the natural environment to promote well-being, focusing not on setting specific timeframes or frequencies for these moments. In essence, the emphasis lies on the meaningful connection with nature beyond mere contact [44]. Additional studies controlling for connection variables, environmental factors in the intervention settings, and even the type of intervention and its outcomes need monitoring for more conclusive insights into the topic.
Regarding the periodicity of the sessions, when applicable, variations were found between one day and seven days of weekly intervention. Interventions were also found that included a stipulation of five times a week for six months or a one-off intervention at first and a second experiment four weeks later. No linearity was found among the articles regarding periodicity, and it was not possible to establish guidance on an “ideal periodicity”.
Concerning the condition of the elderly population involved in the studies, most of them (n = 8) were carried out with elderly people with pre-existing diseases and conditions, such as physical diseases such as hypertension [18,36], diabetes [38], Chronic Obstructive Pulmonary Disease [39], and chronic heart failure [40,41] and mental illnesses such as depression [33] and Alzheimer’s [37].
In analogy with studies that are external to those included in the present study, there is a significant gap in the scientific literature on health promotion and disease prevention in the elderly. The specific approach aimed at this population in relation to contact with nature is scarce, and the existing studies focus mainly on pre-existing diseases and the benefits of contact with nature as a complementary treatment for these diseases [8,45].
Regarding the type of nature-based intervention performed among the studies analyzed, it is possible to observe that among the five types surveyed—forest bathing, forest sound, hiking in natural areas, therapeutic garden, and virtual reality—there is a heterogeneity of form of contact with nature. Nature-based interventions were carried out as direct contact, exemplified by forest bathing, hiking in natural areas, and therapeutic gardens, and also as indirect contact, such as forest sounds and virtual reality.
It is important to highlight that there are differences between direct contact with nature, such as forest bathing, and interventions involving indirect contact, like virtual reality. Both have their benefits and limitations and act through different mechanisms in promoting well-being. In direct contact, the sensory experience is enriched, as all senses and proprioception can be stimulated and integrated. Additionally, the role of certain volatile organic compounds and the natural microbiota of the environment seems to be associated with immune function [46].
On the other hand, there are circumstances where being physically present in nature is not possible, or for some individuals, it may not be preferable due to a dislike of insects, fear of animals present in the experience, or a greater affinity for the digital world over the natural. In such cases, alternative measures can be implemented. Virtual reality serves as a feasible intervention to provoke emotions [47]. It is expected not to have as direct an effect on the immune system, since it will not be activated in the same way. However, the psychoneuroimmunological system might have some potential for activation, although this has not been conclusively proven in research regarding this type of intervention. Yet, undoubtedly, the brain and aesthetic processing of this experience can also produce well-being [48], albeit in a more limited way, as neurosensory stimulation is restricted, since it is an artificially created natural environment mediated by technology. Nevertheless, both interventions can yield effects stemming from aesthetic appreciation, which also mediates neurotransmitters that are capable of promoting well-being [49].
As a society, there is a prejudgment that only direct and physical contact with nature brings benefits to our physical and mental health. However, research—whether or not evaluated in this study—has shown that even indirect contact, through images of nature, for example, has numerous benefits for chemotherapy patients [50], thus promoting equity of access to nature and its benefits, without necessarily being in it, for reasons of fragility due to illnesses and injuries, as in the case of many elderly people.
Finally, the survey conducted by the authors provided evidence that nature-based intervention promotes beneficial effects on the health of older adults. As a limitation of the study, the wide variation in interventions, control groups, and outcome measures among the included studies, such as duration, periodicity, and study population, limited the use of pooling of results, and this diversity contributes to a downgrading of the evidence. Nevertheless, this study offers relevant insights in several areas. In the field of management, it serves as a tool to support and develop programs and public policies that promote and encourage healthy aging, in line with the Decade of Healthy Aging, an action of the World Health Organization (2020–2030) that aims to promote a positive and active approach to aging [51]. Also, it opens space for discussions with health professionals about nature-based practices and care services, both directly and indirectly, in individual or group approaches, aiming at a holistic and equitable approach for older patients. In addition, in the research area, this study fosters the need for studies (mainly randomized controlled trials) within the theme addressed in the countries of the Southern Hemisphere, especially in Brazil, where the present study was carried out.
However, we observe that the number of randomized controlled trials on nature-based interventions is still quite limited, not only in the aging field but in other clinical contexts as well, where observational studies constitute the majority of research on this subject [52].
There are numerous challenges when conducting studies with this methodological design. While they produce a higher level of evidence and allow for discussions on cause-and-effect relationships and intervention efficacy, they are more difficult to conduct. They rely on participants’ availability to be in the field, demanding time, financial investment, and more complex logistics for operationalization.
Society’s awareness also contributes to the evolution of clinical research, yet it remains one of the greatest challenges. This sector is still underexplored and underpublicized, even among healthcare professionals. Additionally, there is widespread consensus regarding the lack of awareness concerning the effectiveness and cost of nature-based solutions (which can include nature-based health interventions) among the general public and key stakeholders, including service users and healthcare professionals. Issues of sporadic and unsustainable funding, leading to a dependence on continuity and volunteer capacity, as well as challenges in offering and maintaining urban green spaces and access to protected areas, are highlighted [53].
Natural experiments have been suggested as a robust alternative to clinical trials, especially when randomization of experiences of the intervention is unfeasible or unethical [54]. Natural experiments also offer a rigorous design and perhaps the only realistic way to measure the co-benefits of nature-based interventions in communities. However, as these natural experiments occur in real-world conditions, they are inherently complex and involve multiple layers of perspectives, values, and trade-offs. Researchers have proposed recommendations for conducting this type of investigation, emphasizing the genuine synergy between conservation biology, public health, and social science research to benefit human and planetary health. Despite the challenges in scientific research in this area, studies are necessary to advance our understanding of the efficacy of nature-based interventions, allowing for their safe implementation in public health [55].
Finally, Brazil, a country known for its immense wealth of biodiversity, becomes a favorable and rich environment for conducting research related to the theme of Nature and Health. This wealth of biodiversity enables a wide range of studies on the interactions between nature and human health. Research on the theme can cover the exposure of nature-based interventions for mental and physical well-being, in addition to indirectly impacting environmental conservations, since people who have greater proximity, familiarity, and connection with nature exhibit greater engagement in environmental conservation actions, thus contributing not only to scientific knowledge, but also to the promotion of a sustainable use of natural resources and to improving the quality of life of the elderly population.
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