Keywords

1 Introduction

Outdoor recreation in natural environments is increasingly recognized as important for improving human health and well-being, especially in urbanized societies with diminished possibilities for human contact with nature [1,2,3]. The global COVID-19 pandemic has further highlighted the enormous value of engaging with nature and the strong need for a mutually advantageous relationship between humans and the natural environment [4].

Nature-based Alpine health tourism can play a significant role in this context. The benefits of human interaction with natural Alpine health resources are manifold and range from acute stress relief [5], reduced symptoms of specific indications such as allergies and asthma and chronic low back pain [6,7,8,9] to improved immune responses [10], cardiorespiratory fitness and quality of life [11]. This exceptional healing potential builds a promising base for the development of evidence-based health tourism products and value chains that are mutually beneficial for tourists and local inhabitants in terms of sustainable regional development.

However, this potential has not yet been fully exploited by Alpine regions. There is obviously a lack of applicable knowledge on the health benefits of specific Alpine resources, resulting in an insufficient innovation capacity of tourism regions. Therefore, within the project HEALPS,Footnote 1 20 Alpine health resources have been identified and characterized regarding their health tourism potential based on the available body of evidence. This research built the base for the project HEALPS2Footnote 2 that is focusing on the development of innovation strategies and hands-on tools to valorize this knowledge.

The present chapter highlights the results of the literature research on the health effects of Alpine health assets focusing on nine resources that are most promising for the development of evidence-based health tourism in terms of push & pull factors (see Table 1).

Table 1 Alpine natural resources as basis for health tourism development
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2 Alpine Health Tourism Potential—Push And Pull Factors

The enormous health tourism potential of Alpine regions is not only made up of the unique health-promoting characteristics of Alpine natural resources—hereby referred to as pull factors—but also of the partly unhealthy habitats and resulting lifestyles in major source markets. The latter are referred to as push factors and are closely linked to the increasing global urbanization. The most relevant push factors in terms of health tourism are shortly described in the following.

2.1 Air Pollution

Environmental pollution is a major challenge to our modern society, as it is one of the most important threats to human health. Air pollution is composed of airborne particles and gaseous pollutants, such as nitrogen dioxide and ozone. Generally, airborne particles can be determined as ambient airborne particulate matter (PM), which is grouped as coarse, fine, and ultrafine particles (UFPs) with aerodynamic diameters within 2.5–10 μm (PM10), <2.5 μm (PM2.5) and <0.1 μm (PM0.1) [12].

A wide range of studies has documented the association of PM2.5 air pollution exposure with morbidity and mortality from respiratory and cardiovascular diseases. There is strong evidence that PM2.5 exposure attributes to specific diseases such as asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, cancer, type-2 diabetes, neurodegenerative diseases, and even obesity [13,14,15,16].

From a geographic point of view, the Alpine region stands out in terms of air quality. Looking at an air quality map of Europe, the Alpine arc looks like a green island in a sea of grey fine dust, offering not only perfect conditions for diverse sports activities but also clean and fresh air [17].

2.2 Noise Pollution

An equally significant push factor is environmental noise exposure in relevant urban source markets. Environmental noise is defined as noise emitted from all sources except industrial workplaces. One in three individuals is annoyed during the daytime, and one in five has disturbed sleep at night because of traffic noise. There is sufficient evidence from large-scale epidemiological studies linking the populations’ exposure to environmental noise with adverse health effects. Noise seriously harms human health and interferes with people’s daily activities at school, at work, at home, and during leisure time. It can disturb sleep, cause cardiovascular and psychophysiological effects, reduce performance and provoke annoyance responses and changes in social behavior [18].

2.3 Reduced Microbial Diversity

Expanding urbanization is also a major factor behind rapidly declining biodiversity. Research suggests that in urbanized societies, the rarity of contact with diverse environmental microbiota negatively impacts immune function and ultimately increases the risk for allergies and other immune-mediated disorders [19].

Although further research is warranted, the microbial diversity of Alpine natural environments could be a promising development field for Alpine health tourism, e.g., regarding the prevention of allergies and asthma (see also Sects. 3.1 and 3.3).

2.4 Lack of Physical Exercise

Besides harmful environmental parameters, urbanization goes hand in hand with the development of sedentary lifestyles. The result of declining physical activity is an increase of disabilities and diseases [20, 21]. The pandemic of physical inactivity is associated with a range of chronic diseases and early deaths. Strong evidence shows that physical inactivity increases the risk of many adverse health conditions, such as the world’s major non-communicable diseases (NCDs) of coronary heart disease, type 2 diabetes as well as breast and colon cancer. In addition, it is responsible for a substantial economic burden [22, 23].

Alpine regions offer a variety of sports opportunities, and holidays in Alpine regions are strongly associated with mountain hiking, biking, climbing, etc. Tailored health tourism products and services based on various physical exercise components could represent not only health benefits for tourists but also contribute to public health.

2.5 Loss of Contact with Nature

Another impact of increasing urbanization is the loss of contact with nature. This ongoing loss of human interaction with natural environments is viewed as one of the most fundamental obstacles to addressing global environmental challenges. Especially children are becoming less likely to have direct contact with nature. Research shows that children’s affective attitudes and willingness to conserve biodiversity are positively associated with the frequency of both direct and vicarious experiences of nature. Children who frequently experience nature are likely to develop a greater emotional affinity to and support for protecting biodiversity. Therefore, children should be encouraged to experience nature and be provided with various types of nature experiences [24].

Moreover, being connected to nature and feeling happy are connected: People that are more connected to nature tend to experience more positive affect, vitality, and life satisfaction compared to those less connected to nature [25]. Nature-relatedness is furthermore a distinct predictor of many happiness indicators [26].

The desire to reconnect to nature offers a variety of opportunities for health tourism development in the Alpine region, especially in protected areas.

3 Evidence as a Strategic Development Factor in Alpine Health Tourism

Product authenticity in the sensitive field of personal health is an essential prerequisite for a responsible relationship with the guest. Therefore, the medical proof of expected respectively promised health effects is a condition ‘sine qua non’ in health tourism [27, 28] and referred to as evidence-based. This notion means that all health-related interventions within a tourism product must be developed and evaluated on the basis of the best available current scientific research and integrate guests’ interests, values, and needs [29].

As research is growing in the field of nature-human interaction, evidence-based health tourism development is a promising strategy for innovative and sustainable regional development in the Alpine region. In the following, the health tourism potential of nine unique Alpine health resources is discussed, considering their respective body of evidence obtained from the biomedical database Pubmed [30]. The level of evidence regarding the individual publications refers to the system of six levels of evidence developed by the Agency for Healthcare Research and Quality [31] (see Table 2). Evidence level Ia represents the highest possible level of evidence, and evidence level IV the lowest. In this way, also research gaps were identified.

Table 2 Evidence levels of the agency for healthcare research and quality (AHRQ)
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3.1 Alpine Farming And Alpine Pastures

With regard to the health effects of Alpine farming and Alpine pastures, environmental microbes are of particular interest. The microbiome is currently a hot topic in the scientific community as well as in the mainstream media. Within the period of 2012–2017, the number of scientific publications increased by up to factor three [32]. Regarding asthma specifically, accumulating evidence indicates that the environmental microbiome plays a significant role in asthma development. The lower prevalence of asthma in populations exposed to farm environments indicates its potential for disease prevention. This protective effect is associated with the specific microbial diversity in a farming environment, especially those with livestock [33].

The human microbiome is defined as the collection of all microorganisms, including bacteria, archaea, and fungi, living in and on the bodies of humans. The microbiome seems to affect virtually every bodily function. Depending on its composition, it can produce thousands of different biologically active substances, including neurotransmitters such as dopamine, serotonin, and norepinephrine. According to the current state of science, the diversity of the microbiome seems to play the biggest role in human health. It is becoming increasingly apparent that the composition of the intestinal microbiome beginning in utero has long-term consequences on human health and well-being. It is therefore extremely important for the maintenance of health to allow the human microbiome to have a lively exchange with microbes from the environment. However, increasing urbanization and changing lifestyles (e.g., more sedentary lifestyles) reduce the spectrum of microorganisms we are exposed to. Studies show that people living in densely populated areas are less susceptible to microbial diversity than people living in rural neighborhoods, which also reduces the diversity of the human microbiome. There is emerging evidence that biodiversity loss in the wider environment might lead to reduced diversity in human microbiota, and these modifications are associated with a dramatic increase of immune-mediated diseases including metabolic, allergic, and inflammatory diseases and most likely also neurodegenerative and psychiatric disorders [32, 34,35,36,37,38,39].

Asthma and allergies are the most common chronic diseases in children and the leading causes of school absences, chronic medication usage, emergency department visits, and hospitalizations, which affect all members of the family and represent a significant societal and scientific challenge [40]. There is strong evidence that the development of allergic sensitization can be influenced by environmental co-factors. A large body of literature shows that children raised on farms have much lower rates of allergies and asthma. As early as the late 1990s, Von Ehrenstein and colleagues [41] as well as Riedler and colleagues [42, 43] found that farmer’s children have a lower prevalence of hay fever, asthma, rhinoconjunctivitis as well as other atopic diseases and concluded that increased exposure to bacterial compounds in stables with livestock prevents the development of allergic disorders in children (level III). These findings could also be reproduced in other authors [see, e.g., 44–48]. There is a solid body of evidence that exposure to a greater variety of environmental microorganisms explains a substantial fraction of the inverse relation between asthma and growing up on a farm [49]. One key reason might be that the kids breathe in air full of molecules from the cell wall of certain bacteria, called lipopolysaccharides for their fat sugar structure. Also known as endotoxins, these fragments—from dying bacteria in cow manure and fodder—cause a temporary low state of inflammation in the lungs that somehow dampens the immune system’s response to allergens [50]. Despite the protective effect of living on a farm, research suggests that even maternal exposure to an environment rich in microbial compounds might protect against the development of allergies and asthma and lead to an upregulation of receptors of the innate immune system [51].

Summarizing, the medical-scientific evidence shows great potential for the development of innovative health tourism products focusing on the prevention of allergies and asthma. Alpine farms and Alpine pastures could represent a valuable resource for city dwellers who are exposed to reduced microbial diversity in their everyday urban life. Current studies show that the timing of exposure to the farm environment is crucial: The strongest effects were observed for exposures that occurred in utero and during the first year of life [52]. Although, most studies in this field are retrospective cross-sectional studies (level III) and not experimental studies. This means that there is still a lack of evidence on the potential effect of health tourism stay on Alpine farms on the human microbiome. Considering the crucial timing of the exposure to farm environmental microbes, future research should focus on assessing the effect of holidays on Alpine farms and pastures for pregnant women or families with kids in their first year.

3.2 Alpine Hiking in High And Moderate Altitude

In the age of industrialization, holidays primarily focused on regeneration, rest, and recreation. The structural shift towards a service-oriented society has led to a change in holiday interests in the Western world. Although rest and recreation are still important to people during their holidays, the range of physical activities carried out while on holiday has grown considerably since the end of the 1990s. Especially hiking is becoming increasingly popular and represents an important travel motive [53]. The main reasons for hiking are experiencing nature, fresh air, the beauty of nature and landscape, fauna, and flora [54]. Another aspect that is becoming increasingly important is health as a motive for hiking holidays, and the scientific evidence of the positive effects of hiking on health and well-being is constantly growing. Exercise in natural environments reduces stress and protects against mental illness more effectively than does exercise in the city or indoors. From a physiological point of view, mountain hiking can be characterized as endurance exercise in nature with predominantly moderate intensity [55]. Thus, hiking is very well suited to respond to changing needs of vacation.

Therapies at moderate to high altitude (between 1500 and 3000 m above sea level) are known to affect a variety of physiological and immunological parameters. These include neurovegetative, cardiovascular, and thermoregulation mechanisms [56, 57], but also the reduction of inflammation and immunomodulatory effects [58,59,60], while additional exercise in these altitudes leads to even stronger effects [61]. In contrast to UV radiation, which increases with rising sea level and is associated with vitamin D synthesis, fine dust pollution is reduced [17]. Furthermore, shorter flowering phases and more extreme weather conditions lead to a change in vegetation at higher altitudes, which significantly reduces allergen concentrations [62]. The lower air viscosity facilitates breathing and stays at moderate altitudes lead to relaxation and stress reduction [63]. Physical activity at moderate sea level leads to a significant increase in hematopoietic progenitor cells, promotes erythropoiesis, and thus increases the number of erythrocytes and oxygen supply [64]. Climate therapy at moderate to high altitude is also well-known as a successful alternative medical treatment for respiratory and allergic diseases such as bronchial asthma, atopic dermatitis, psoriasis or eczema [65,66,67].

One of the first approaches to investigate the health effects of Alpine mountain hiking were the “Austrian Moderate Altitude Studies” (AMAS) that were conducted in Austria. AMAS I (2000) focused on the indication of the metabolic syndrome, a combination of overweight, disturbed blood sugar and blood fat metabolism as well as elevated blood pressure, which are massive cardiovascular risk factors, whereas AMAS II (2006) focused on persons with high-stress levels. The studies proved that an active sojourn (a combination of hiking and active/passive regeneration) at Alpine moderate altitudes (1500–2500 m) under the guidance of professional coaches has positive effects in probands with metabolic syndrome as well as in a clientele suffering from stress [68,69,70]. In addition, physical activity in nature is subjectively perceived as less strenuous, while mental exhaustion and stress levels are reduced. Physical activity in nature also has a mood-lifting effect, increases self-confidence, and the personal state of health is subjectively rated higher. In addition, attention and the ability to concentrate are increased [10, 71,72,73,74].

Niedermeier et al. [74] were able to show in a randomized crossover study that the stress hormone cortisol can be reduced by three hours of mountain hiking with 600 m altitude difference to a greater extent than by relaxation in a quiet place. Walking is good for the bones, prevents osteoporosis-related complaints, and also sustainably increases health-related quality of life (HRQOL), and reduces pain in the 50–65 age group studied [75]. Three-week mountain hiking improves blood pressure and pulse behavior so effectively that even antihypertensive drugs could be reduced and partially discontinued. The body weight decreased significantly, and the vitalizing red blood corpuscles increased. In addition, quality of life improved, and quality of sleep was also positively influenced [68, 76, 77].

Mountain hiking combines concentric and eccentric training: When walking uphill, the muscle overcomes gravity by contracting or shortening the muscle fibers (= concentric). The main load factor in uphill walking is, therefore, almost exclusively concentric. Walking downhill, on the other hand, requires the muscle to counteract gravity by lengthening in a controlled manner (= eccentric). Regular eccentric training leads to positive adaptations in the areas of strength and kinematics (biomechanics). In addition, positive metabolic adaptations can be induced by eccentric loads. Due to the lower cardiopulmonary load, people with cardiovascular diseases (e.g., in the initial rehabilitation phase) can also benefit from this form of exercise. For people with low cardiorespiratory fitness, walking downhill is ideal training for later tours with a slight ascent [78].

During mountain hiking, mountaineers are confronted with often rapidly changing environmental conditions like slope of the path, stony or narrower passages, altitude, weather conditions, ascending and descanting sections. These constantly changing conditions require constant proprioceptive feedback, thus promoting the diversification of gait patterns and balance responses [79]. Mountain hiking could therefore be an effective training for older people, addressing both aerobic capacity, strength, and balance.

The health tourism potential of Alpine hiking can be seen as very high in Alpine regions. In product development, it should ideally be combined with other location-bound natural resources that could provide additional health benefits, such as balneotherapy or waterfalls. The beneficial effects of balneotherapy are widely used to treat musculoskeletal diseases, to improve immunity, and relieve pain [80]. Bathing in thermal water triggers several physiological responses like vasodilation, gate control mechanism, elevation of beta-endorphin levels, and muscle relaxation, which could positively affect regeneration after exercise like, e.g., mountain hiking. The additional integration of location-bound resources contributes to the development of a unique health tourism appeal as they are geographically specific and cannot be exported [29]. Another element for health tourism differentiation in the field of mountain hiking is the development of target group-specific products. Hiking trails have different characteristics that can be developed for specific indications like, e.g., cardiorespiratory fitness, chronic low back pain, etc.

3.3 Alpine Milk And Dairy Products

An old farmer’s proverb says that the grass is always better the higher one goes, and at the top it is so good that even farmers might like to eat it. In fact, with increasing elevation, plant growth diminishes and with it the yields; but since the intensity of sunshine increases, Alpine plants process greater amounts of energy that leads to a higher protein and fat content. Animals react in a similar manner. Because of the demands of Alpine living on their bodies, animals are slower to fatten than during the same length of time in the valley, and milk output at higher altitudes is much lower than in the valleys. Although, it is also creamier when manufactured at higher elevations. Still today, it contains between 15 and 30% more fat than in the valley. What is more, Alpine products were considered to be tastier and healthier because of herbs found only there, containing high percentages of ethereal oils [81].

The local flavor of the high mountainous meadows shows up in their products, which is why the cheeses were named after the Alpine pastures where they were produced. Urnerbödeler, Saanen, or Emmentaler cheese: whole regions were identified with certain types of cheese. The links between landscape, animal, and product represented a strain of thought with several components. The notion of dairy practices encompassed perceptions about the influence of the terrain on plants, animals, and their products. When the first naturalists and doctors directed their attention to the Alps, they soon discovered these links. Hippolyt Guarinoni, a doctor and humanist in the sixteenth century, stated, e.g. that the products of the lowlands could not match the quality of Alpine products [81].

Dairy production therefore has a long tradition in the Alpine region and has soon been associated with beneficial health outcomes. Milk and its derivates are useful foods throughout all life periods, in particular during childhood and adolescence, as their contents of calcium, protein, phosphorus, and other micronutrients can promote skeletal, muscular, and neurologic development. Especially Alpine milk and Alpine dairy products seem to have a health-promoting nutritional value due to their composition. Generally, milk from grass-fed livestock is more beneficial than that of corn-fed animals [82]. It could be shown that cheese made from cows grazed on Alpine pastures have a more favorable fatty acid profile than other cheese types. Alpine cheese may be a relevant source of Alpha-Linolenic acid (ALA), which is cardioprotective [83].

Several studies also show that—especially unpasteurized—Alpine milk consumption may prevent the development of allergies and asthma. Similar to the exposure to environmental microbes on farms, farm milk consumption during pregnancy and early childhood shows the strongest effect. However, it has to be mentioned that most studies are cross-sectional (level IIa) [84, 85]. These associations do not confirm a causal relationship, and further investigation to identify specific protective agents or mechanisms is required. Some cohort studies have already been undertaken that support the protective effect of milk consumption (level III) [42, 86]. Although, more cohort studies are necessary to clarify the temporal sequence of exposure and outcome to identify critical periods of childhood when exposure to these putative protective agents or mechanisms might operate. It is also important to mention that unpasteurized milk consumption is not hazard-free, as milk-related outbreaks of Cryptosporidium species, Campylobacter species, and Escherichia coli O157 have been described [87]. Therefore, it is important to understand which components and mechanisms are underlying the observed protective effects and risks to ultimately be able to utilize milk as a means of primary prevention. Until then, the consumption of raw milk cannot be safely recommended [88].

Nevertheless, Alpine dairy production plays a key role in the protection of the Alpine flora and fauna as well as in the preservation of regionally typical landscapes. It is also integral to the ecological structure and cultural identity [81] and can therefore be a valuable product component in Alpine health tourism.

3.4 Balneotherapy/Hydrotherapy/Healing Waters

Balneotherapy has a long tradition in Alpine regions and is traditionally used for a variety of medical indications like rheumatic, dermatological, pulmonary, or gynecological problems, but especially for disease prevention, stress reduction, and recreation [89]. The terms balneotherapy, hydrotherapy, and spa therapy are often used interchangeably, which is also due to different meanings in different regions and cultures. Generally, balneotherapy involves immersion in mineral and/or thermal waters from natural springs, while hydrotherapy employs normal tap water for medical treatment. Balneotherapy is traditionally practiced in health resorts respectively spa towns with their special therapeutic atmosphere as part of a complex therapy program, which is why the term balneotherapy is often used synonymously for spa therapy. Although, strictly speaking, spa therapy employs a number of different treatment modalities, including hydro- and balneotherapy that is often combined with massage, exercise, physical therapy and/or rehabilitation. Obviously, this lack of consensus on terminology as well as the regional and cultural differences regarding the application of balneotherapy, represent a major barrier in medical research and reduce the performance of meta-analyses and systematic reviews [90]. This has to be taken into account when assessing the medical evidence of Alpine balneotherapeutic interventions. Considering the sheer amount of studies on balneotherapy, the focus here is on the highest evidence level, namely systematic reviews.

To date, there are three CochraneFootnote 3 reviews (level Ia) on balneotherapy focusing on indications that are commonly treated with balneotherapy: osteoarthritis, rheumatoid arthritis, and venous insufficiency. Regarding osteoarthritis, it was found that spending time in a mineral bath compared to no treatment may improve pain and quality of life [92]. Pain severity of patients with rheumatoid arthritis can also be reduced through balneotherapy. Although, the overall evidence is insufficient to show that balneotherapy is more effective than no treatment due to the low quality of the provided studies that could be included in the review [93]. Finally, the review on chronic venous insufficiency provides evidence of low to moderate certainty in the choice of balneotherapy in quality of life, pain, and changes in skin pigmentation. Most individual studies report positive results but do not provide sufficient evidence to support the data due to the small number of participants and limited data [94].

In summarizing, the strength of the body of evidence regarding balneotherapy is insufficient and positive outcomes of individual studies should be viewed with caution. This is not due to the general lack of medical research in this field but due to the poor methodological quality of studies. There is a high risk of bias in most studies as well as a lack of adequate statistical analysis and data presentation [92, 94].

Balneo- respectively spa therapy is a huge economic factor for many Alpine regions. Although, public cutbacks have put increasing strain on many balneary regions and spa towns. Health insurances incrementally ask for reliable evidence on the effects of the individual therapy. Therefore, high-quality research is needed, focusing on appropriate allocation concealment as well as adequate data analysis and presentation [92, 94]. Furthermore, future studies should also conduct cost-effectiveness analyses, as these could be a valuable argument when it comes to resource allocation in healthcare policy [90].

One approach to innovative research in health tourism regarding balneotherapy is to assess not only the effect of the individual balneotherapeutic therapy but to assess the potential benefits of a whole health tourism product in comparison to a standard holiday. Using this approach, Prossegger and colleagues [80] could show that a seven-day intervention with moderate mountain hiking in combination with balneotherapy is an effective training for older persons, inducing short-term improvements in static balance and quality of life. Based on these findings, regional health tourism development processes were initiated, and target group-specific products and service chains were created and positioned on the market [95].

3.5 Forest/Forest Therapy

In recent years, there has been considerable and increasing attention to using the forest environment as a place for recreation and health promotion. This trend derives from Japan, where it is called “shinrin-yoku”, which is a term that means “taking in the forest atmosphere through all of our senses” or simpler “forest bathing”. Since the development of the concept during the 1980s, considerable scientific research on its health effects and the mechanisms behind the healing effects was conducted [96]. The first studies were conducted on the Japanese island Yakushima (shima = island in Japanese). Yakushima includes a ≈19,000 ha area as a biosphere reserve. The island is located at a biogeographic boundary between tropical and temperate regions and contains a remarkably wide variety of flora: There are evergreen broadleaf forests, conifer, 2000-year-old cedar trees, and nearly 2000 different plant species [73]. Most other forest study sites have similar characteristics. This is important to mention when it comes to discussing the transferability of study results from tropical/south Asian forests to European resp. Alpine forests. Reported health benefits from forest therapy studies include impacts on humans’ immune system, boosting natural killer cells and anticancer proteins, reduced stress, improved mood, sleep, and well-being, reduced blood pressure, accelerated recovery from illness, and increased ability to concentrate [97,98,99,100]. Based on these results, more than 50 Forest Therapy Trails were developed in Japan with millions of annual visitors, and forest therapy has become a cornerstone of preventive health care and healing in Japanese medicine. Also, in other Asian countries like China and South Korea, forest therapy has become very popular, and the trend is now also emerging in Europe [101].

There are more than 150 publications on forest therapy (including keywords “shinrin-yoku”, “forest therapy”, and “forest bath”) listed in PubMed [30]. Despite this large body of literature, the evidence base for health benefits attributable to forest therapy is rather low due to methodological weaknesses. Oh and colleagues [102] conducted a systematic review on forest therapy, where only six randomized controlled trials (RCT, highest evidence regarding single intervention studies) met the inclusion criteria. These criteria were based on the assessment of methodological quality according to the Cochrane risk of bias (ROB) tool. The review found that the included six RCTs reported promising therapeutic benefits of forest exposure on several physical and psychological conditions, including hypertension, cardiac and pulmonary function, stress, immune function, inflammation, oxidative stress, stress hormones, anxiety and depression, and emotional response; although, outcomes of anxiety and depression had mixed results and some inflammatory biomarkers showed no results. The review concludes that there is a consistent trend in a broad range of health outcomes, suggesting potential for forest bathing. Although, the authors state that the included studies had a high risk of bias. Due to this lack of high-quality studies, there is no convincing evidence of the benefits of forest therapy. Furthermore, none of these studies were registered in the international trial registry.

Within five years since the publication of Oh and colleagues’ review, only six further randomized controlled trials were published (also not registered at the ISRCTN). Two of them were conducted in China and showed beneficial effects on patients with chronic heart failure [103, 104] (level Ib). Another study from China examined the psychological effects of forest therapy [105]. Also, in China, Kim and Shin [106] investigated whether there is a difference between guided and self-guided forest therapy (level IIa). In both cases, positive psychological effects have been shown, but they do not seem to be generally transferable. The remaining two studies were conducted in Denmark and Sweden and could not show any difference between forest therapy and control group regarding physiological parameters [107, 108] (level Ib and Iia). However, both studies found positive effects on psychological parameters such as stress and anxiety. A recent pilot study from Italy also focuses on psychological effects and confirmed the positive effects on stress and anxiety [109] (level Iia).

Besides the lack of methodological quality, there are further limitations on the transferability of study results to Alpine forests. Research suggests that many measured health effects are attributed to phytoncides, which is a generalized term for natural chemicals released by plants into the environment. It is theorized that these chemicals could influence stress physiology and immunology through inhalation. Most forest therapy studies were conducted in tropical primeval forests (mostly Japanese, Korean, and Chinese) with a high biodiversity [73]. These forests are totally different from typical Alpine forests. Almost all Alpine forests are semi-natural, as defined by Forest Europe, with a significant presence of large trees and deadwood. There are almost no truly primary forests and plantations [110]. Thus, also their phytoncide composition is totally different. The measured effects can therefore not be transferred to Alpine forests. In most studies, the control group stayed in Asian megacities like Tokyo, with high air and noise pollution. The measured health benefits can, therefore, also be attributed to the absence of these factors. Furthermore, these cities are not comparable to typical European/Alpine cities. Additionally, most studies on forest therapy have been conducted with male Asian subjects [111], which is a further limitation on transferability. An approach to analyzing the health potential of alpine forests according to current medical scientific standards is shown by Pichler and colleagues in their method paper presenting a randomized controlled clinical trial that compares two types of nature-based interventions in South Tyrol [112].

Considering the rich occurrence of forests in the Alpine region and the emerging trend towards nature-based recreation, forests may be considered as an important resource with a high health tourism potential. As a base for health-promoting activities, forests not only offer potential for longer stays: also, short-term stays seem to have a positive effect, especially on psychological aspects of stress and anxiety. In this respect, forests can also be thought in terms of a local health-promoting recreation for urban areas. However, based on current data, no scientifically founded statement can be made about the specific health effects of Alpine forests.

3.6 Protected Areas And Biodiversity

The Alps are among the richest regions of Europe regarding the variety of landscapes as well as plant and animal species. As the loss or destruction of habitats is the most direct threat to biodiversity, protected areas are crucial to counter the continuing loss of ecosystems and species [113]. There are nearly 1000 protected areas in the Alps, covering a surface area of over 53,000 km2. The protected areas cover roughly 28% of the Alps [114]. The Alps are thereby one of the world’s most important ecoregions in terms of conserving global biodiversity [113].

According to the Convention on Biological Diversity (Article 2), biodiversity means the variability among living organisms from all sources, including inter alia, terrestrial, marine, and other aquatic ecosystems and the ecological complexes of which they are part. This variability includes diversity within species, between species, and of ecosystems. This definition reflects different levels of biodiversity, including genetic diversity, species, and ecosystems [115].

Closely linked to biodiversity is the environmental microbial diversity that influences the human microbiome, which is the collection of microorganisms including bacteria, archaea, and fungi living in and on the bodies of humans. This is an emerging research field in medical science and holds significant health tourism potential as a specific Alpine resource.

Biodiversity and human health are interlinked in various ways. A large body of papers regarding the effects of protected areas on human health focuses on the provision of ecosystem services. For example, Harrison et al. [116] showed that nearly two-thirds of the global population rely directly on protected areas for freshwater provision. Also, protected areas play an important role in providing pollination services for food production or in contributing to air purification and temperature regulation. Another important role of protected areas is the conservation of medical plants and the numerous recreational services provided by protected areas that promote a healthy lifestyle [117]. The most well-researched aspect of the direct link between protected areas and human health is the effect on psychosocial well-being. Protective areas have a strong restorative capacity and have shown to foster recovery from mental fatigue, reduce stress levels, assist cognitive functioning, and improve the overall psychological state [117, 118]. Some studies show that these psychological benefits are higher in areas of greater biodiversity [119, 120]. Furthermore, research indicates a potential beneficial and protective influence of residential areas with a high biodiversity on respiratory health [121].

Studies that contribute to the understanding of positive health outcomes of protected areas and biodiversity are mostly conducted in Australia [120, 121] or Scandinavia [122]. No intervention study could be identified that explicitly links Alpine-specific protected areas to direct health outcomes.

Although, based on the indirect links of protected areas and biodiversity to human health and well-being, it is evident from the authors’ perspective that there is a huge health tourism potential. Also, protected areas play a key role in the conservation of other Alpine natural resources with medical-scientific proof, such as waterfalls, and can therefore be seen as “meta health resources”. However, the research base regarding studies that specifically address the role of protected areas in supporting human health is generally low. Biodiversity-health linkages have often been explored by looking at ecosystem service flows like, for example, water and energy provision but are rarely taking protected areas as a leading analytical unit. Consequently, health outcomes of protected areas have been largely overlooked [117]. Therefore, there is both a strong need and potential for research programs that foster health-biodiversity linkages, especially in terms of Alpine protected areas. To fully exploit the resulting health tourism potential, research projects should be characterized by a strong integration of the protected area’s management and the tourism industry.

3.7 Speleotherapy/Radon Therapy

Speleotherapy is a special kind of climate therapy which uses the specific microclimate of mines and caves to treat especially respiratory and skin-related diseases. Speleotherapy is relatively widespread in Europe. Speleotherapy facilities vary in their environmental conditions, including radiation level, temperature, and humidity. In most caves, patients are advised to rest during this period. In some caves, physical exercises or breathing exercises, including the inhalation of salt aerosols, are recommended.

A meta-analysis of the health effect of Speleotherapy with respect to chronic asthma was conducted by Beamon et al. [123] (level Ia). Only three studies met the inclusion criteria. This already shows the problem that there are too few studies to date to be able to make a reliable statement on the effect of Speleotherapy. Therefore, the authors conclude that further randomized controlled trials with long-term follow-ups are necessary. Gaus and Weber [124] demonstrated that a 3-week Speleotherapy intervention significantly improved the FEV-1Footnote 4 of children aged 4–10 years with bronchial asthma up to one week after intervention. Although, it is not clear from this study whether a long-term improvement can be induced. However, it was shown that Speleotherapy is an efficient and safe form of therapy for children with bronchial asthma. Overall, there is little scientific evidence on Speleotherapy. Caves and mines differ in their specific conditions. Therefore, further research is needed to evaluate its specific effects.

One form of Speleotherapy is based on the use of radon. Since the beginning of the twentieth century, radon therapy has been applied in middle Europe. Radon therapy uses the chemically inert naturally radioactive gas radon to treat various diseases. Its main application is found as a non-pharmacological treatment option for various inflammatory rheumatic diseases. For treatment purposes, radon is commonly applied by bathing for about 20 min in water with a radon concentration of 0.3–3 kBq/L or staying for about 1 h in caves or galleries with natural radon concentrations of about 30–160 kBq/m3.

Currently, relevant studies on radon are available for different indications. A meta-analysis of Falkenbach et al. [125] examines the effect of radon therapy, including Radon Balneotherapy and Speleotherapy, on pain reduction in rheumatic diseases (degenerative spinal disease, rheumatoid arthritis, and ankylosing spondylitis) (level Ia). No immediate effects were found, but significant improvements in pain were found three and six months after treatment. Overall, however, the meta-analysis concludes that further studies on radon therapy are needed. Other studies are concerned with the treatment of rheumatoid arthritis and osteoporosis. Osteoporosis is a widespread systemic skeletal disease characterized by decreased bone mass. Secondary osteoporosis is a frequent complication of rheumatoid arthritis. Winkelmayr et al. [75] compared low-dose radon hyperthermia treatment with either radon thermal water or radon-free thermal water in combination with mountain hiking (level Ib). Both interventions produced statistically equal results: Significant immediate and long-term effects on regulators of bone metabolism and somatic complaints were observed. Another study of low-dose radon hyperthermia therapy examined the effects of hyperthermia treatment on osteoporosis in patients with rheumatoid arthritis compared with patients with osteoarthritis [126]. Serial low-dose radon hyperthermia therapy causes an increase in bone-building cytokines and a decrease in bone-catabolic cytokines in rheumatoid arthritis. Also dealing with rheumatoid arthritis were Franke et al. [127] (level Ib). This study investigated the effects of radon baths on rheumatoid arthritis in contrast to artificial CO2 baths. Long-term improvements in pain intensity, as well as reduced doses of corticosteroids and NSAIDs (non-steroidal anti-inflammatory drugs) and/or analgesics, were observed in the radon group. On the same topic, a multi-center study investigated the effects of radon spa therapy in comparison to placebo applied on health resort out-patients [128]. Radon spa therapy improved pain relief and analgesic drug consumption. No effects regarding quality of life were observed. Significant benefits were found until six months follow-up, but not until nine months follow-up. In a pilot study, beneficial effects of radon spa therapy on the total antioxidant status were observed [129]. In addition, Passali et al. [130] analyzed the effect of radon hot spring therapy in a narrative review that included four prospective studies. Considered were asthma, respiratory tract inflammation, and nasal obstruction, and allergic rhinitis. Improvements in nasal resistance, air flow, mucociliary clearance, and ciliated to muciparous cell ratio and FEV-1 in asthmatic patients were observed. Finally, a study on pain and hypertension investigated the effect of low-dose radon spa therapy [131]. Patients with chronic painful musculoskeletal diseases received either radon balneotherapy or radon CO2 balneotherapy. The radon CO2 treatment effectively relieved pain. Furthermore, a reduction in blood pressure could be observed in patients who received the radon CO2 treatment.

Apart from the therapeutic application of Speleotherapy, the historical caves and tunnels are very well suited for the creation of unique experiences and educational purposes. In this way, they have the capacity to meet leisure, tourism, and healthcare needs.

3.8 Waterfalls

The Alpine region hosts numerous waterfalls that produce nano-aerosol, a particularly valuable feature in terms of the healing potential of the Alpine region. Nano-aerosols are nanometer-sized electrically charged atomized water droplets of waterfalls. The charged nano-aerosol is formed within microseconds after the ionization of primary ions due to hydration and cluster ion formation processes. Waterfalls mainly produce negatively charged ions, referred to as ‘Lenard ions’. As a result of the aerosolized water hitting the ground, the droplets created in the waterfall form dipoles with a negatively charged surface. Due to the waterfall wind, the negatively charged particles, atomized by thermophoretic processes, drift away from the waterfall, whereas the positively charged droplets quickly sink to the ground. This causes a surplus of negatively charged air ions in the proximity of the waterfalls, which can be of the order of several 10.000 ions/cm3 of air. The diameter of these negative air ions is between 1.5 and 10 nm, whereby 2 nm sized negative ions are most abundant. Their lifetime is long enough to be inhaled. The remaining bigger fragments are positive and precipitate to the ground [132,133,134].

Traditionally, numerous beneficial health effects have been attributed to waterfalls. Although, to date, only a few waterfalls have been evaluated according to the criteria of evidence-based medicine regarding their potential health benefits. The first randomized clinical trial (RCT, level Ib) on this was conducted by the research group of Arnulf Hartl at the Paracelsus Medical University in Salzburg, who assessed the Krimml waterfall aerosol’s effect on clinical, functional, molecular and immunological parameters of allergic asthma. Imbedded in an asthma camp, 54 children aged 8–14 with mild to moderate bronchial asthma spent three weeks in the National Park Hohe Tauern in the Federal State of Salzburg, Austria. The patients were divided into two groups: Both groups spent a daily hour outdoor exposition, the waterfall group close to the Krimml waterfalls and the control group 6 km away. Living, housing and nutrition, and other daily activities were completely identical in both groups. Over the three weeks of exposure, the waterfall caused a balancing immune modulation characterized by a change in the ratio of allergic/anti-allergic regulatory T-cells. While both groups benefited from the high-altitude therapy in the National Park Hohe Tauern in terms of a reduction of asthmatic symptoms, only exposure to the waterfall improved pulmonary function by 30% with a measurable effective duration of at least two months. Furthermore, the asthmatic symptoms of the waterfall group were significantly alleviated compared to the control group even four months after exposure [134, 135].

Also, the second RCT (level Ib) on the effect of waterfall aerosols was conducted in the National Park Hohe Tauern, although in their southern Carinthian part at the Gartl waterfall. In a three-armed RCT, the effect of the waterfall was assessed on immunological reagibility, physiological stress, and stress-related psychological parameters. People with moderate to high stress level spent an active sojourn with daily hiking tours in the National Park Hohe Tauern, Carinthia, Austria. Additionally to hiking, half of the group was exposed to the Gartl waterfall aerosol for one hour a day, while the other half of the group spent the same time at a distant site at the same altitude. A third control group stayed at home. Results showed an improvement of lung function and most physiological stress parameters in both intervention groups compared to the control group. Additionally, waterfall-specific positive effects on the immunological reagibility as well as on psychological stress parameters were found. Thus, the study data indicate an influence of the waterfall ionosols on complex psychoneuroimmunological regulatory circuits [10], which could be the basis for the development of health tourism products and service chains focusing on the prevention and therapy of chronic stress.

The health tourism potential of Alpine waterfalls is enormous. For example, based on the medical research of the Krimml waterfalls, the health tourism initiative ‘Hohe Tauern Health’ was developed that promotes evidence-based health tourism products for the target group of allergic and asthmatic guests [136]. This initiative has developed into a major economic and innovation factor as it led to the creation and higher qualification of job profiles and triggered cross-sectorial regional innovations such as allergy-friendly timber construction [137].

Although every waterfall has its own physical signature and different waterfalls thus have different effects on human physiology [138]. Therefore, the development of health tourism products based on the health effects of Alpine waterfalls has to go hand in hand with medical research, ideally with a clinical study on the potential health benefit of the individual waterfall.

3.9 Winter Activities

During winter, cities in major Alpine source markets are often characterized by a high level of air pollution. In addition to the year-round fine dust producers such as traffic etc., the heating period significantly increases particulate matter emissions. Furthermore, temperature inversion leads to increased winter smog. Compared to urban environments, fine dust pollution is extremely low in Alpine mountainous regions, and they are therefore perfectly suited for exercise in clean and fresh air.

Winter activities in Alpine regions are still predominantly snow-based, like Alpine skiing, cross-country skiing, ski mountaineering, and snowshoeing. Alpine skiing is the main reason for winter holidays in the Alps. Besides its fun factor, it also has positive effects on our health and well-being. It is e.g. an efficient way to increase cardiorespiratory fitness, measured in increased maximum oxygen uptake (VO2max) [139] (level IIb). Skiing primarily trains leg muscles, but arm and upper body muscles are also exerted. Considering the breaks during lift rides, Alpine skiing burns about 400 kcal per hour. However, the study by Stöggl et al. only considered high-intensity Alpine ski training. Since skiing promotes leg strength and balance, it can be an effective preventive measure for the growing target group of best agers (60 years and older) to maintain physical fitness and prevent falls. These positive effects were confirmed by Muller et al. [140] in a study with an investigation period of twelve weeks (level Ib). Skiing also reduces cardiovascular risk factors and prevents atherosclerosis and type 2 diabetes, and is also a safe exercise for elderly people regarding cardiovascular risks [141,142,143] (all level Ib). A reduced sympathetic activity induced by skiing was found in middle-aged men, which has an additional cardioprotective effect [144] (level Iib).

Cross-country skiing is another winter sport that offers a wide range of health benefits, while there is only a low risk of injury and sports-related consequential damages:

Cross country skiing is a full-body workout that uses and strengthens all major muscle groups in arms, chest, back, abdominals and legs. Furthermore, cross-country skiing is an excellent training for the improvement of cardiorespiratory fitness: cross-country skiers exhibit some of the highest maximal oxygen uptake (VO2max) values [145] (level Iib). Within one hour, about 800–1000 kcal are burned during cross-country skiing. Research shows that cross-country skiers suffer less frequently from overweight, show better health behavior, and their risk of developing cardiovascular disease is significantly decreased [146] (level III). Furthermore, the risk of cancer, as well as the overall mortality rate, is reduced, as shown in a cohort study comparing Swedish cross-country skiers with the general population [147]. A follow-up Finnish population study with over 2000 participants confirmed these results by showing that general mortality is inversely and independently associated with frequency and duration of recreational cross-country skiing [148] (level III).

Ski mountaineering is one of the leading trends in Alpine winter sports. The rewarding effect of an adventurous descent on ungroomed slopes after a strenuous climb through untouched winter landscapes clearly has addictive potential. However, in order to prevent injuries a certain level of fitness is required. Ski mountaineering is a high-intensity sport and is, therefore, an excellent training for the improvement of cardiorespiratory fitness [149] (level III). Consequently, the prevalence of cardiovascular diseases in ski mountaineers is much lower compared to the general population [150] (level III). Furthermore, ski mountaineering does not only train endurance and strength, but can also be used as a recovery and regeneration measure [151]. Haslinger and colleagues could show that ski mountaineering is even safe for people with total knee arthroplasty [152].

Snowshoeing is an Alpine winter sport that can be compared to Nordic Walking. It is a full-body exercise that is easy on the joints and suitable for all ages and fitness levels. Snowshoeing burns up to twice the number of calories as walking at the same speed (up to 1.000 cal per hour) [153]. Furthermore, in comparison to walking, snowshoeing recruits more muscle groups. Especially for women, often wearing high-heels snowshoeing can be beneficial, as negative effects like a tightening of the hamstring can be counteracted [154].

Considering the need for winter product differentiation with regard to climate change as well as changing customer demands, winter hiking is a promising field of development. It is possible on all hiking trails that are approved and mapped as such in terms of avalanche danger and walkability in winter. The calorie consumption for one hour of winter hiking is around 250 kcal. Exercise in fresh air and sun releases the happiness hormone serotonin, which counteracts both physical stress reactions and the “winter blues” thus lifting mood [155, 156]. Winter hiking also reduces physiological parameters such as blood pressure and heart rate, supports weight loss and improves cholesterol and sugar metabolism [70, 76, 157, 158]. It is particularly suitable for overweight people and those affected by metabolic syndrome (high blood pressure, abdominal obesity, fat metabolism disorders, and increased blood sugar). Furthermore, winter hiking in moderately cold temperatures reduces airway inflammation levels (measured as fractional concentration of exhaled nitric oxide (FeNo) as well as the number of eosinophil cells in the nose and induces sustainable improvements of allergic symptoms [80] (level Ib). Winter hiking is suitable for all age groups and can especially address families.

Currently, health tourism offers and initiatives predominantly focus on summer holidays, whereas the health tourism potentials in Alpine winter tourism have not yet been exploited. As shown above, also the winter season offers a variety of opportunities to develop evidence-based health tourism products. Furthermore, the development of winter health tourism products can be a strategy to react to the already noticeable impacts of climate change with rising snowlines and shorter winter seasons. Especially winter hiking products can contribute to a diversified product range to reduce snow-reliance.

4 Conclusion

Evidence-based health effects of Alpine natural resources are a promising starting point for the development of health tourism products and enhance the innovation capacity of tourism regions. The presented body of evidence regarding the health benefits of nine selected Alpine resources highlights the enormous health tourism potential but also reveals research gaps. Moreover, it was demonstrated that not every measured health benefit of a specific and location-bound health resource is transferable to the same resource in another region: The example of Alpine waterfalls shows that similar resources may trigger different health effects. Therefore, when regional health tourism development processes are initiated, there is a strong need for early integration of medical research and intense dialogue between tourism and medicine throughout the development process. Furthermore, a successful health tourism product is in most cases, not solely based on one specific resource but combines the unique assets of the individual region—not only in terms of natural environments but also in terms of culture, services, cuisine or infrastructure. An approach to the assessment and evidence-based combination of these regional key performance indicators (KPIs) is presented in the contribution in this book by Bischof & Hartl “KPI for data-driven assessment and benchmarking of potential development paths for nature-based health tourism in the Alpine region”.

As Alpine tourism regions are required to differentiate their tourism products to compete in an increasingly competitive and cluttered global market, the valorization of Alpine natural health resources and other unique regional assets represents a crucial success factor for tourism innovation and regional development strategies. If the resulting regional development processes follow a science- and sustainability-driven approach, each resulting health tourism product will contribute to the positioning of the Alpine region as a globally attractive health-promoting place for guests and the local inhabitants, while promoting local competence and future-proof value creation.