How does nature affect mental health?
I love going for a walk in any kind of natural environment. I enjoy the exploratory aspect, for the most part, but there is also something intensely soothing about being near trees. Recently, when there were lots of articles about the Japanese practice of shinrin-yoku (forest bathing) in the UK news, I did a bit of digging in the research literature.
Before we start, let’s note that there are very few studies in this area of research that talk about walking rather than any other type of physical exercise – say, using your arms to roll a wheelchair. However, a lot of studies have explored the effects of simply viewing nature (even virtually) as opposed to moving around in it, and those effects are generally positive too. These results are therefore probably generalisable to other forms of physical movement in natural environments.
There are lots of physiological effects of taking a walk in nature. For example, it lowers blood pressure (in men, compared to walking in an urban area [i]) , lowers stress hormones (in men, compared to walking in an urban area [ii]) and improves lung function (in elderly women, compared to walking in an urban area [iii]. Yes, it did take me a while to find a study that wasn’t only about men, how did you guess?
So, a forest walk is better for your physical health than a city walk, which will surprise no-one who has lived or worked in a big city. Are there also psychological effects?
An aside about the state of your mind
There are lots of different perspectives in psychology and philosophy about what exactly the mind is. The current dominant perspective in the psychological world is a type of monism (see e.g. Spinoza’s Ethics): the brain and the mind are one and the same thing, so that a change in the state of the brain is the same thing as a change in the state of the mind.
We can contrast this to dualism (see e.g. Déscartes’ Mediations on First Philosophy), where the mind is a non-physical entity that is separate from the brain, so that a change in the state of the brain does not imply a change in the state of your mind.
I hope you haven’t got a headache yet, because I want to introduce you to a third view, embodiment.
In embodiment, the brain is simply a part of the mind, which arises out of the interaction of the body with the world. Varela, Thompson, and Rosch say that this interaction is of two sorts. One is the raw interaction of sensing and responding to the world, and the other is the cultural and biological context in which that raw interaction takes place. A change in the body or the wider context can therefore effect a change in the mind - for example, a child using toys to act out a story as they are reading will remember and understand the story better than a child who just reads.
What does this have to do with walking children in nature? My point is that if, like me, you are an adherent of the embodiment view of the mind, it might be entirely pointless to draw a distinction between physiological and psychological effects of being in nature. All we’re really doing is looking at different levels of explanation. Nonetheless...
We learned a few weeks ago that an increase in stress hormones can have a negative effect on memory. We know that forest walking can decrease stress hormones, from the Park et al. study above. Does that mean it also has a good effect on memory? Yes! Berman, Jonides and Kaplan [iv] asked their participants to remember strings of numbers and recite them backwards (the backwards digit span task, if you’re feeling fancy) before and after a walk. They sent some of their participants on a walk in a city, and some in a park, and found that the people who’d been on a walk in the park got better at the backwards digit span task, while the people who’d been on a walk in the city didn’t. (So there’s some extra advice if you’re jetlagged: go for a walk in park if you can!)
Sure, take a pillow if that’s your jam. I’m not the boss of you.
It’s not completely clear why walking in nature is good for us, but Kuo [vii] has a great review of 21 possible mechanisms for this effect, including:
Many plants release phytoncides, chemicals which can lower blood pressure and improve immune function.
The sights and sounds of nature can help the body heal itself.
Nature often provokes feelings of awe, which can reduce the body’s level of inflammatory cytokines (proteins the immune system produces in response to threats).
Contact with nature helps us sleep better, which has a wide range of health benefits.
Kuo suggests that most of these mechanisms have one central driving factor: improved immune function. She theorises that spending time in nature has a number of ‘active ingredients’ like phytoncides and improved air quality, which impact on the immune system directly as well as through psychological, physiological and behaviour changes (e.g. relaxation, lowered blood glucose, and better sleep), all leading to improved physical and mental health.
Be careful where in nature you walk; some parts are pointy and may not be good for your health
I was lucky enough to grow up in the countryside, and to consistently have had access to natural environments even as an adult living in a city. Not everyone has these privileges. Aside from campaigning for the provision green spaces even in places that are largely populated by poor people and people of colour (I’m looking at you, Los Angeles), what can you do if you’re far away from natural environments or lack the resources to get to them?
Maas and colleagues [viii] found that some of the link between access to green spaces and physical and mental health is explained by social interaction – for example, being able to interact with others makes you feel less lonely, which in turn makes you feel happier. They didn’t actually test whether this social interaction was happening in the green spaces, though, which means that just hanging out with other people (even in an urban environment) might be a key to improving your health, perhaps by helping you feel less lonely.
One other option is virtually experiencing nature, i.e. Youtube. A bit of googling led me to a rich seam of virtual nature walks like this one.
Watching videos of natural environments has positive effects on mental health [ix], though they’re not as strong as the effects you’d get from the real thing, and it’s not clear whether there are also positive effects on physical health. However, if you’re far away from nature, housebound, have hay fever, or just don’t fancy going out because the weather’s horrible, it’s probably worth watching one of those videos instead of an episode of The Good Place – or maybe as well as an episode; it’s a great show.
[i] Li, Q., Otsuka, T., Kobayashi, M., Wakayama, Y., Inagaki, H., Katsumata, M., ... & Suzuki, H. (2011). Acute effects of walking in forest environments on cardiovascular and metabolic parameters. European Journal of Applied Physiology, 111(11), 2845-2853.
[ii] Park, B. J., Tsunetsugu, Y., Kasetani, T., Kagawa, T., & Miyazaki, Y. (2010). The physiological effects of Shinrin-yoku (taking in the forest atmosphere or forest bathing): evidence from field experiments in 24 forests across Japan. Environmental Health and Preventive Medicine, 15(1), 18.
[iii] Lee, J. Y., & Lee, D. C. (2014). Cardiac and pulmonary benefits of forest walking versus city walking in elderly women: a randomised, controlled, open-label trial. European Journal of Integrative Medicine, 6(1), 5-11.
[vi] Park, B. J., Furuya, K., Kasetani, T., Takayama, N., Kagawa, T., & Miyazaki, Y. (2011). Relationship between psychological responses and physical environments in forest settings. Landscape and Urban Planning, 102(1), 24-32.
[viii] Maas, J., Van Dillen, S. M., Verheij, R. A., & Groenewegen, P. P. (2009). Social contacts as a possible mechanism behind the relation between green space and health. Health & Place, 15(2), 586-595.