Interview/ Kathy Willis, professor of biodiversity, the University of Oxford, and author, Good Nature
The practice of forest bathing is a mindful, meditative experience where we allow our senses to become attuned to nature by spending time walking through woodlands. Numerous studies have shown that immersing ourselves in the natural world in this way can have significant health benefits, but could we ever bring this practice to a clinical setting?
The answer to that question is the subject of the new book Good Nature by Kathy Willis, professor of biodiversity at the University of Oxford. In it, she draws on the available evidence to show not just the health benefits of being surrounded by nature, but also the quantitative data that shows how doctors could prescribe time in the natural environment.
In this interview, she explains how specific types of nature can help us relax and even improve our gut microbiome. Edited excerpts:
What is the mechanism in the body by which seeing plants and nature can have not just a psychological impact, but a physiological one, too?
When you look at the colour green―and green and white leaves in particular are good―we've got three pathways that are affected through that visualisation. (It's an automatic response. We have nothing to do with it. So, for example, it'll be a change in your hormone levels, your adrenaline hormone will go down or your heart rate variability is enhanced.) The first pathway affects the autonomic nervous system, so your heart rate and your blood pressure goes down. The second one is your endocrine system―your hormones―and, for example, you get a change in your salivary amylase levels, which is one that shows stress levels are reduced. The third one is your psychological index, which is the sort of thing that a psychiatrist will do to show people feel calm and a lot less anxious.
Is this response something thatwe have evolved?
It may well be, and it's quite interesting because we have a particular response to different shapes of horizons. Think about an open landscape with a few oak trees, or a conifer outline, which is pointy, versus an angled and squared urban outline. What studies have shown is that when we look at the horizon, our eyes are picking out the fractal dimension (the complexity of an image's detail), and we automatically tend to go for fractal dimensions which are mid complexity (1.3). I've done it many times with audiences, and people put their hand up to say which horizon makes them feel most relaxed. People always choose the more open landscape with a few scattered trees on it, which is 1.3.
Those tree shapes are reminiscent of savanna [landscape], and there was a really nice study where they showed photos of different landscapes to teenage children and young adults from West Africa. They would live their whole life in tropical rainforest and hadn't travelled, and yet they still picked the open savanna landscape as the one that they most liked.
I guess all the senses must be impacted in some way by just being surrounded by nature?
Yes, but the point is that it's not all nature, it's specific types. The chapter that most surprised me was the one on smell. Before I started researching smell, I just assumed you walk somewhere, breathe in a nice scent and then breathe it out again. But actually, when you breathe in a plant scent, those molecules are volatile organic compounds (VOCs) that pass across your lung membrane into your blood. So if you walk in a pine forest you have higher levels of pinene in your blood and that is interacting with the same biochemical pathways as taking a prescription drug for [a] particular thing [such as anxiety].
Really interesting studies have been done... when you breathe in, particularly from the Cupressaceae family and the cedar family. [In experiments, when people inhale VOCs from these trees] it not only reduces their adrenaline hormone, but elevates the natural killer cells in their blood. And the natural killer cells are the things that attack cancers or viruses.
There's a lovely study published in Oncotarget, a cancer journal. [In it] they had looked at people who lived close to Cupressaceae forest versus those who live further away―the ones that live beside the forests were much healthier, with much less occurrences of many autoimmune type diseases. [Also] they entered a group into a Cupressaceae forest and measured their nature killer cells. After the five-hour walk, they had really elevated natural killer cells in their bloods [but] even more important was that seven days later, they still had greatly elevated natural killer cells in their blood. So there's not only short-term, but also long-term benefits.
Are there any other bodily systems that are affected by nature?
We' ae learning so much about the gut and the gut flora, and how [it is affected by] going into a more biodiverse environment. Even just walking on the edge of the park, the more biodiversity you have at different levels, the higher the environmental diversity of that microbiome. And when you're in it, in the same way as smell, your body takes on the signature of the environment it's in.
They showed it beautifully with Finnish nursery children. In a study, [they observed children playing in] three nursery playgrounds―one had concrete, one had matting, and in the third one soil brought in from the Boreal forest. Over 28 days, the children played in the different areas, and then [the researchers] measured their gut microbiome, their skin [microbiome] and then they measured the inflammatory markers in their blood. Those that played in the Boreal forest [soil] saw a completely new gut microbiome after 28 days, but not only that, these children also had this statistically significant reduction in inflammatory markers.
And then they showed the same with adults who had a green wall in their office versus no green wall. These plants and this biodiversity is seeding the environment that these people are in and they are adopting that signature as a result of it. Given only 7 per cent of our flora is inherited, the rest is driven by the environment, wherever we are, we should all really be heading towards the bushy edges.