Introduction
Several recent reviews have concluded that, while certainly not a panacea, exposure
to nature and outdoor activities can improve mental health for at least some symptoms,
causes, patients, and circumstances (1–6). They are particularly relevant for the
psychological components of chronic disease syndrome, namely depression and dementia
(7–9). Outdoor exercise plays a role, in addition to outdoor environments (10–12),
but nature-based outdoor activities yield benefits additional to those of exercise
alone (13–17). Outdoor therapies can also assist in overcoming some types of chronic
pain (18). They are valuable at all ages, from children (19, 20) to seniors (21, 22),
and for those with both minor and severe clinical symptoms (23). All of these have
substantial economic implications (6, 24, 25).
Currently, however, outdoor therapies have limited deployment, especially in wealthy
urbanized nations where they are most valuable. Government health agencies, and private
health insurers, run educational and marketing campaigns, but these are for voluntary
patient-funded activities. There are various school and youth adventure education
programs (19, 20), but these are preventive rather than therapeutic. A few countries
have trialed so-called green prescription programs (26), but too small and short to
be effective. Some privately run programs may be more successful (27), but they are
targeted to specific market sectors, unconnected with mainstream health care. None
of these yet provide for routine diagnosis and prescription of outdoor therapies,
for patients who present themselves at their general practitioners with mental health
concerns. Here, therefore, we consider what additional research may be required to
achieve this. There are both social and technical aspects.
The key social obstacle is that outdoor therapies are not yet perceived as mainstream
medicine. Even though the practical delivery of outdoor therapies is very similar
to widely prescribed physiotherapies and psychotherapies, outdoor therapies are not
yet available through publicly or insurance-funded medical diagnosis, prescription,
and providers. They are offered principally by private providers, who are forced to
adopt business and marketing models more closely aligned to discretionary activities
such as the fashion and beauty industry. Historically, similar social obstacles were
also faced, and overcome, by many other components of modern health-care systems.
It takes time, institutional change, and technical information for them to become
routine (1, 6).
Here, we focus on the technical obstacles and the research required to overcome them.
Recent reviews agree that knowledge of the therapeutic links between nature exposure
and mental health is currently only at proof-of-concept stage, and research is now
required to elucidate dose–duration–response relationships (1, 4, 6). We endorse this
view and propose two additional areas of research. The first additional area is to
differentiate (a) patient symptoms and personality traits and (b) characteristics
of therapies, to prescribe specific therapies that match particular patients and conditions.
The second is to test the social levers needed to persuade individual patients to
adopt and follow through with courses of outdoor therapies once prescribed.
Characteristics of Patients and Therapies
Research to date has shown that nature exposure can provide a wide range of mental
health benefits, related to attention and cognition, memory, stress and anxiety, sleep,
emotional stability, and self-perceived welfare or quality of life (1–9, 13, 15–17).
As yet, however, there have been no systematic comparisons, cross-testing different
outdoor therapies for different mental health conditions. Individuals differ greatly
in their psychological and physical capabilities and interests, for different outdoor
activities. Some individuals may not be keen to try any outdoor therapies at all.
Some patients and conditions may not respond to any outdoor therapies. For those patients
and conditions that do respond, different types and intensities of outdoor therapies
may prove more effective for different individuals and mental health conditions.
We propose, therefore, that we need to consider these differences explicitly as we
establish data on dose, duration, and response, so as to generate a portfolio or menu
of outdoor therapies that can be matched to individual patients. Quantifying any individual’s
mental health, so as to measure their responses to outdoor therapies, requires a suite
of parameters. We can differentiate patients on the basis of symptoms, personality
traits or types, capabilities, and interests. These are analogous to factors such
as patient body weight, allergies, and drug sensitivities in the use of pharmaceutical
treatments, and are equally important. To take just one example, some individuals
have sensation-seeking personalities (28), whereas others do not.
Previous research has included many types and intensities of nature exposure, ranging
from views from a window (29) to adventure sports involving skill, thrill, and risk
(30–33). We can differentiate therapies on the basis of: duration, repetition, and
frequency; features of the natural environments concerned; patient activity, including
type, degree of physical exercise, and degree of potential risk; and emotional components,
such as thrill, fear, or joy (30–33).
Some of these correspond to dose and treatment regime in pharmaceutical therapies,
whereas others are analogous to active agents. The former include: the length of each
individual period spent outdoors; the time of day when it occurs; the number of occasions
per day, week, month, or year; and the overall duration of the treatment regime. The
latter include: the ecological, esthetic, and social characteristics of the natural
setting where the outdoor activity takes place (34–36); and the type and characteristics
of the activity itself (32, 33). Activity characteristics include: physical exercise;
strength and skill; risk and thrill; social interactions involved; instructor-led
or self-paced; equipment used and safety procedures followed; emotional setting and
consequences; and social perception of the activity among the patients’ friends and
families, peers, and the general public.
Diagnosis, Design, and Implementation
Diagnostic tests, questions, and observations are needed to select, design, and prescribe
specific outdoor therapies for individual patients. Since research to date is neither
systematic nor comprehensive, an adaptive learning approach will be needed. This is
acceptable, since the risks are low. Outdoor therapies involve multiple small doses
over an extended period of treatment. Treatment regimes can easily be adjusted if
adverse effects are detected, or if the dose proves too small to be effective. The
primary positive therapeutic effects of outdoor therapies can be detected by individual
patients and described to prescribing practitioners, during the course of the therapy.
This contrasts with many other types of therapy, where the patient may only be able
to detect negative side effects. If a practitioner prescribes an outdoor therapy regime
that is too powerful for a particular patient, analogous to exceeding drug tolerance,
then the patient simply will not have the physical capability to perform it.
As more people adopt organized, well-defined, and regular outdoor therapies, this
will provide opportunities to conduct large-scale longitudinal studies, evaluating
outcomes for individuals with different personalities and prior mental health conditions.
This applies whether those organized programs are prescribed or self-adopted (27).
Participants could provide individual information to an anonymized central repository,
in return for comparative information about their place in an overall population.
This would gradually establish a data set for multivariate analysis, to identify the
most effective treatments for patients with different symptoms and personality traits.
Alternatively, meta-analyses of data sets published with more restricted studies may
yield similar results.
Meanwhile, one option is to create a menu of outdoor therapies as a basis for discussion
between patient and practitioner, to allow for a voluntary selection. There are a
number of considerations. The first is safety: what can the patient be expected to
do, without putting themselves at risk? For example, a person with cognitive impairment
might not be able to navigate outdoors without assistance. Second, what is the patient’s
physical skill and capability? For example, a person who is old, unfit, or overweight
might be unable to complete a long outdoor hike, even at slow speed under easy conditions.
Third, what are the patient’s prior skills? For example, a person might have prior
expertise in photography, plant or animal identification, or a range of adventure
recreation activities. Fourth, what does the patient know and enjoy about outdoor
nature? In particular, do they prefer passive contemplation and observation, or active
exercise?
The menu need not provide a perfect match between patient and therapy, because outdoor
therapies are easily adjustable, with low risk of adverse effects. The limiting factor
is neither diagnosis nor detailed design, but implementation: persuading patients
to commence and persevere. We suggest that simply providing people with information
about individual benefits is ineffective. More successful strategies seem to be those
that package outdoor therapies as purchasable products. The most effective bundles
include multiple social levers operating in parallel (27). Two levers are particularly
powerful. The first is social justification, to allow individuals to enjoy spending
time and funds on personal outdoor nature-based activities, without criticism from
family or friends. The second is mutual peer support, to prevent relapses under competing
pressures.
Here, we suggest two more: an immediate emotional benefit and an irrecoverable investment.
If participants feel happier after spending time in outdoor nature, they will find
ways to do so more often. And if they have paid in advance for an experience or program,
they are less likely to cancel. Commercial tourism products such as wildlife safaris,
for example, satisfy both these criteria. Products offered by some enterprises also
contribute directly to the well-being of impoverished communities and the conservation
of threatened plant and animal species, adding the social altruism lever identified
in previous research (27). In contrast to past public health initiatives relying on
untargeted education, therefore, we suggest that designing and marketing highly targeted
commercial programs may prove more effective. In slogan form: sell, do not tell.
Author Contributions
All authors contributed to research. RB wrote final text.
Conflict of Interest Statement
The authors declare that the research was conducted in the absence of any commercial
or financial relationships that could be construed as a potential conflict of interest.
The reviewer STE and the handling Editor declared their shared affiliation.