Why mention D.A.R.E., the Drug Abuse Resistance Education (D.A.R.E) 1 program that was rolled out in 1983 as the model program to prevent children and youth from using drugs in a blog for NCH2? Because as researchers we are often asked why there is a need for more research on the health benefits of engaging with nature when it seems so clear that nature is good for us. Research is needed because there are many unanswered questions about who benefits from engaging with nature, and why, what “nature” means to different people, and what the best practices are for helping diverse people gain the beneficial effects of nature. These questions are at the center of a recent article by Phi-Yen Ngyuen, Thomas Astell-Burt, Hania Rahimi-Ardabili, and Xiaoqi Feng in The Lancet Planetary Health.2
In 1983 political leaders thought D.A.R.E. was wonderful, until they didn't. Retrospective analysis showed that D.A.R.E. in its original form, did not reduce drug use or save lives, and may have increased drug use. The D.A.R.E. program has since been reconfigured and the new program has very different goals, however the journey of D.A.R.E from a $10 million/year drug prevention program to a program that “teach[s] students good decision making [sic] skills to help them lead safe and healthy lives” is illustrative of the importance of rigorous program evaluation and research. 1
Ngyuen et al. (2023) conducted a systematic review and meta-analysis of peer-reviewed papers that describe original research or evaluation of nature prescription programs. For their paper, the authors describe a nature prescription as “typically involve[ing] a health professional (e.g., a general practitioner) or social professional (e.g., a counselor or welfare officer) recommending a patient to spend a fixed amount of time a week in a natural setting, such as a park.” This definition was used to identify publications that contained information about programs that were either described by the original authors as a nature prescription program or fit the description of a nature prescription program regardless of whether the original authors used the specific term “nature prescription.”
Systematic reviews of randomized control trials are the pinnacle of the hierarchy of evidence recognized by biomedical researchers.3 The reason for this prominence is that systematic reviews use rigorous methodologies to examine the existing literature to draw conclusions about the weight of evidence from many studies. This is much stronger than relying on what any single study shows. Meta-analyses add an additional level of strength by using statistical methods to compare the results of the reviewed articles to provide an estimate of the overall size of the effect of the various interventions. Effect size tells us how large the response is, and whether the response is likely to be clinically relevant, not just whether it is statistically significant. Conducting a meta-analysis requires that the methods used by different researchers be sufficiently well described and sufficiently compatible that they can be compared directly. Systematic reviews also examine the extent to which the body of literature may be influenced by bias, either intentionally or unintentionally.
Nguyen et al. initially found 4,309 records of peer-reviewed publications that might fit the objectives of their review. They included randomized and non-randomized controlled trials. However, further winnowing using approved procedures for systematic reviews resulted in only 92 papers that were appropriate for the systematic review and 28 that could be included in a meta-analysis. Papers were excluded from the review if they described interventions such as building new green spaces, outdoor gyms, programs requiring “high levels of safety and skilled organizers (e.g., wilderness adventures)”, etc. Papers were included if the intervention “…took place in a park or was organized by a health or social institution for patients or clients and used nature-based therapy to improve health outcomes…” The analysis examined what age groups were studied, which pre-existing conditions patients had, what types of settings were used, the types of activities recommended, and the health outcomes measured (“physical, psychological, or cognitive health, and behavioral outcome”) .
Their analysis showed that nature prescriptions do lead to better outcomes than the control (usual or standard care) for systolic and diastolic blood pressure, depression and anxiety, and greater increases in daily step count. Nature prescriptions, however, did not lead to an increase in medium to vigorous physical activity, the type of physical activity needed to provide many health benefits. Additionally, while many individual papers reported improvements in many other physical health measures (e.g., improved balance, reduced pain) there was insufficient evidence to draw generalizable conclusions. Thus, those of us who advocate for nature prescriptions need to be cautious when we make claims about specific health benefits.
Nguyen et al. also report that most of the studies they examined had a high risk of bias. They found multiple sources of bias, the most obvious being that it is nearly impossible to “blind” either the researchers or the participants to the intervention they are receiving. People know where they are walking and spending time. Another source of bias is the small sample sizes used in individual studies and high numbers of people who drop out of the studies before they are completed. We must ask ourselves these high dropout rates are telling us about how nature prescriptions are implemented.
However, the strength of systematic reviews and meta-analyses, is that if multiple small studies show the same trends, we are probably onto something. Importantly for those interested in health equity, the literature is heavily biased toward people from a few populations. Most studies of nature prescriptions are done in high-income countries, most interventions took place in South Korea, the U.S.A., or Japan. Studies are also limited in their recruitment of individuals from socioeconomically disadvantaged groups, only 11% of studies recruited participants from these groups. Thus, we should question how generalizable the results are among cultures.
What does this mean for the use of nature prescriptions? Nguyen et al. have done researchers and practitioners of nature prescriptions a huge service by pointing out where we have strong evidence for the benefits of nature prescriptions, and by showing us where there are weaknesses in the evidence. If we are to build policy and programs using nature prescriptions, it is important for us to know whether those programs and policies are created in a way that will benefit the people for whom they are intended, whether they are sufficiently feasible and attractive that people will stick with them. This is why NCH2 was created around a culture of research and evaluation. NCH2 seeks to share both what we know and don’t know about the health benefits of engaging with nature, and to encourage a community that contributes to building that evidence base.