The Science Behind the Claims
Read Time 11 minutes ~ 2100 words
If I didn’t have my own personal experience , I would be skeptical of the headlines about the mental health benefits of nature.
Here’s how I tried to sort through the evidence on nature, well-being and mental health.
As a psychiatrist, I frequently get asked by patients – and friends and co-workers – about various supplements, online apps, programs, or therapies claiming to treat various health conditions.
The mental health field seems particularly prone to these types of claims. This is likely due to both how common mental health problems are in society, and the complex and poorly understood root causes of many psychiatric conditions.
However, because I “experimented” on myself – observing differences in how I feel before and after contact with nature – I became curious about evidence for nature (you can read my first post for more on this).
Balancing the Headlines with Evidence
I am a psychiatrist and my research training is in clinical epidemiology. In my academic work I am a skeptic. I tend to be cautious when reading claims of mental health benefits of what may be considered complementary and alternative medicine approaches.
No doubt there is some fluff out there about the benefits of nature. This is true with many claims promoting health benefits with simple sounding approaches to complex topics as psychological wellbeing.
However, behind the headlines and pitches for nature cures there actually is some science. Actually, there is quite a lot of science. And as we’ll see, there is some fairly convincing evidence that nature can “cause” improvements in mental health.
An overview of the scientific evidence for the health benefits of nature found contact with nature to be associated with:
- Improved quality of life, life satisfaction, happiness, and well-being
- Mental health conditions – symptoms of depression, anxiety, stress, attention-deficit hyperactivity
- Physical health – general health, mortality, pain
- Medical conditions – blood pressure, obesity, heart failure, diabetes
In this post, I will review the evidence to find out if nature is truly making people happier and healthier.
This is a big topic with plenty of active research. Therefore, I started with the best evidence I could find related to quality of life, well-being, and mental health symptoms and focused on adults.
There will be some future posts on Nature Brain about nature’s impact on children and seniors. We’ll also have future posts on topics physical health or medical conditions.
An Epidemiological Approach
In my academic work as an epidemiologist I frequently answer questions of causation – whether one thing is responsible for a change in another.
In medicine, there are a few ways to try to establish causation. There are several methods used to investigate causation and a general ranking of these approaches is sometimes used to assess the level of evidence.
The first approach is the tried and true scientific experiment. You expose one group to one condition – more time in nature – and compare it to another group – spending time in a non-nature setting.
You can then assess for differences between these groups on some outcome such as happiness or reported stress.
In the medical field experiments – usually referred to as randomized controlled trials – are considered the strongest evidence for causation.
Multiple experiments on the same topic can sometimes be combined in a technique called meta-analysis. It can be used summarize the results from multiple studies to get an overall effect.
The results of meta-analyses are often presented as effect sizes. Some of the results I found for this post used effect sizes to assess the how big or strong the associations between nature and mental health is (more information on effect sizes is available here if you are interested).
You don’t need the gory details about effect sizes but a little information here might help.
Larger effect sizes generally mean “bigger” effects. Effect sizes of less than 0.1 are considered small effects, 0.3 are medium or moderate effects (which are the typical size of effects observed with mental health treatments) and effect sizes of 0.5 or larger are usually considered large or strong.
So with that out of the way, let’s get on to what I actually found!
The Experimental Evidence for Nature
I approached this question as I would any other in my research. First, started with trying to identify the highest quality evidence (meta-analyses and experiments). Then, I planned to climb my way down the evidence ladder if needed.
Finding Evidence for Nature
To find this evidence I searched Google Scholar and Pubmed (two online sources for identifying medical research literature). I plugged in terms for using terms for nature, ecotherapy and meta-analysis (although not the most rigorous search it is a pretty good place to start).
Around 1,000 hits came back from the search. As is usually the case, many of the results were off topic. However, I did find several studies that were relevant to my question.
From this initial list I summarized what I think were the best studies summarizing nature’s effects on well-being and benefits for mental health conditions like depression.
To help understand the results in a bit more detail, I grouped the results into two groups. The first includes happiness and well-being.
The other group included other mental health symptoms and conditions like depression or anxiety. While there is some overlap between these topics, there are also important differences.
Here’s what I found.
Nature’s Effect on Happiness and Well-being
The first study was by McMahon and Estes who completed a review of experimental studies of nature. They identified 30 separate studies that assessed the effects of nature on both positive moods and negative moods.
Individuals assigned to spend time in nature had a moderate improvement in positive mood – measured by an effect size of 0.31 – or a moderate, positive association with positive mood.
The effect on reducing negative moods was -0.12, or a small reduction in negative moods associated with contact with nature.
There were benefits noted for both exposures to real natural environments (effect size 0.37) and laboratory simulations of nature (0.26). Both wild and managed (urbanized nature) nature experiences were found to have similar effects.
I found a second review on the relationship between greenspaces and mental well-being was completed by Houlden in 2018. They identified 50 studies that explored the relationships between local greenspaces and well-being and mental health.
Increased access to local greenspaces was positively associated with life satisfaction (termed – hedonic well-being). However, greenspaces did not affect with personal flourishing (eudaimonic well-being). The relationships between mental health symptoms and greenspaces was also limited.
A more recent review by Pritchard reported on associations between nature and hedonic and eudaimonic well-being. Both eudaimonic (effect size 0.24) and hedonic well-being (effect size 0.20) were higher among individuals who spent more time in nature.
Lee reviewed the effects of forest bathing – visiting forests or engaging in viewing forests – on symptoms of depression depression. In a total of 28 studies, 21 (75%) reported some improvement in depression with forest bathing.
The relationship between nature connectedness and happiness by Capaldi found 30 studies. A positive relationship between greater happiness and increased connection with nature was observed (effect size 0.19).
Nature-based recreation includes leisure in the natural environment, and can include urban parks or wilderness settings.
A review by Lackey identified 51 studies on the mental health effects of leisure activities in nature.
They found that 88% of the studies reported improvements in mood or life satisfaction with activities in nature. Three quarters of studies reported improvements in anxiety and stress and 9 of 10 studies found improvements in happiness with nature.
In summary, the relationship between nature and well-being has been subject to large amount of study. Existing research supports small to moderate benefits associated with time in nature.
Nature and Mental Health Symptoms and Conditions
In contrast to the effects of leisure activities on mood and happiness, the effects on diagnosed mental health conditions included fewer studies in the review by Lackey.
Five of the eight studies (63%) reported benefits of recreation in nature for individuals with depression, while one study of post-traumatic stress disorder did not find any effect of nature.
Roberts provided a review of the effects of nature on depressive symptoms. These studies mainly involved healthy individuals who did not suffer from a depressive psychiatric disorder.
Four studies in the review by Lee on forest therapy among people affected by depression or other psychiatric conditions and three of the studies reported some benefits, mainly in symptoms of depression and quality of life.
Overall, the effects of short-term exposure on symptoms of depression had a moderate positive effect (effect size 0.29) in the 33 studies in the review.
There is little research on nature for mental health symptoms or disorders as compared to the number of studies on nature and well-being. However, the results so far also appear to be promising.
A Few Thoughts on the Results
A couple additional comments on what I found. Most of the reviews I found acknowledged to there being some shortcomings of research in this area.
As is often the case in research promising early findings from smaller studies often lead to larger – and better designed – studies in the future. I expect that research on this topic will grow rapidly in the coming years.
It’s important to note that nature did not appear to have any negative effects on people. This might seem obvious, but it is an important point. There are few – or no – side-effects associated with with nature. Nature is safe!
This is one consideration when making potential suggestions to people where evidence might be early or not particularly strong.
How Does Nature compare to Other Healthy Activities?
Nature activities wasn’t directly compared to other activities such as exercise and meditation. As well, both meditation and exercise can be performed in natural or outdoor environments. think that the effects of contact with nature on well-being seem similar to those found with meditation. However, both nature-related activities and meditation can include a variety of approaches so different types of nature and meditation are likely to have different benefits.
Exercise has extensive evidence for improving both well-being and mental health. Nature contact appears to be roughly equivalent to exercise on well-being although may be less effective than exercise in improving symptoms related to mental health disorders.
An important consideration is that connecting with nature likely requires less motivation than starting exercise. In this respect, nature may actually benefit more people overall given how challenging it is for many people to engage in exercise regularly.
In the future, I’ll dig deeper into whether Green Exercise (exercise activities in nature) is better than exercise indoors.
My Verdict on the Evidence: Nature Helps!
Here are my final thoughts on what I found:
- Nature has a fairly consistent positive effect on well-being and mental health
- Most studies report some benefit of contact with nature on well-being and mental health.
- The evidence is relatively strong for nature having a benefit on quality of life, well-being and happiness
- There are fewer studies of nature as a treatment for mental health disorders. This isn’t to say that nature isn’t helpful – it’s just that nature has not been studied as frequently in this situation
While we should all read the headlines with a critical eye, I think its safe to conclude that for most people increasing their time in nature is likely to improve their well-being and may improve their mental health.
In a few weeks, my next post will examine how much (or little!) time we are spending in nature and make some comparisons across different locations.
In the meantime, I welcome your comments on this post or any of the other content on Nature Brain. I hope you all get to spend some time out in nature during these challenging times!