June 27, 2018

A study of the stress-reducing powers of wilderness explores “levels of nature.”

By Alex Hutchinson for www.OutsideOnline.com

One of the things I love about my neighborhood in Toronto is that I’m a block away from the Humber River, a historic fur-trading route that flows into Lake Ontario. Back in 1954, after Hurricane Hazel flooded homes in the valley, the city expropriated a bunch of land and turned it into a linear park meandering through the city, with tens of miles of bike trails and gravel paths running alongside the river.

This happens to be the same neighborhood where I grew up, so I’ve seen the parkland change over the years, from vast swaths of heavily manicured and pesticide-ridden lawn to a more natural mix of forest and unkempt savannah. These days, running on the trails, it’s much easier to imagine you’re in the middle of nowhere. And if you hop into a canoe, you can effectively leave the city behind (as long as you don’t paddle too close to the sewage plant near the mouth of the river).

Playing in my local pseudo-wilderness has always been fun. But it may be more than that. In recent years I’ve started paying attention to a stream of research suggesting that these kinds of natural settings have powerful—and measurable—physical and mental benefits. There have been numerous studies over the past decade or two that follow a similar basic pattern: Ask someone how they feel, test some physiological parameters, then send them to wander around in a forest for an hour and see if their physical and mental health improves compared to a similar walk in the city. The general answer is yes, it does. So the next question is: Why?

new study in the journal Behavioral Sciences, from researchers at Indiana and Illinois State universities, joins the attempt to unravel which factors are most crucial to nature’s restorative benefits. The study compares three different “levels of nature”—a wilderness setting, an urban park, and an indoor exercise club—to see how they affect levels of stress, as measured by a psychological test plus a saliva test for the stress hormone cortisol and an enzyme called alpha-amylase.

The theory is that wilder nature will have more powerful effects, and the researchers offer a few possible reasons for this hypothesis. One is psycho-evolutionary theory, which “posits that natural environments are effective at reducing levels of stress because they offer specific attributes that our species viewed as having inherent survival qualities, such as water and spatial openness.” Another is attention restoration theory, which argues that the irregular shapes and patterns in nature exert a “softly fascinating stimulation” that draws your attention gently, allowing your mind to wander and recover from the near-constant effort of directing your attention in urban life.

The study, which was led by Alan Ewert of Indiana University, involved buttonholing people on their way into the three sites and convincing them to fill out a questionnaire and drool into a sample tube before and after their visits. A total of 105 people participated, most of whom planned to walk or jog in the parks or on the treadmill. The wilderness setting was a 1,200-acre forest called Griffy Lake Nature Preserve; the 33-acre urban park had a playground, walking paths, and grass fields; and the gym was a standard fitness center.

The results were suggestive but not overwhelming. Visitors to all three sites reported decreases in their perceived worries and demands. In addition, visitors to the park and wilderness area had increased levels of joy; and visitors to the wilderness area were the only ones to have a significant decrease in cortisol levels. That’s consistent with the “levels of nature” hypothesis, much like another recent study that saw greater improvements in insulin sensitivity and oxidative stress in Korean women who spent a half-day in a “wild forest” compared to a “tended forest.” But (to pick up on a theme from one of my latest columns) neither of these studies was randomized, so it’s impossible to account for the fact that people who choose to visit a wild place may be qualitatively different from those who choose to head to the gym or the “tended forest.”

Still, even if the answers aren’t yet clear, I think these are the right questions to be asking. A few years ago, I wrote about a really neat study that linked a database of all 530,000 trees planted on public land in Toronto with detailed neighborhood-level health data. After controlling for factors like income, education, and age, the researchers estimated that every additional ten trees on a block corresponded to a one-percent increase in the self-reported health of the street’s residents. “To get an equivalent increase with money, you’d have to give each household in that neighborhood ten thousand dollars—or make people seven years younger,” the lead researcher, University of Chicago psychology professor Marc Berman, told me.

In a separate set of experiments, Berman and his colleagues have been trying to figure out what specific visual cues, like curved edges, color saturation, or randomness, we respond to in nature. Even when you scramble images so that you can’t tell if you’re looking at “natural” scenes, these low-level visual features still predict how people will respond. Most recently, in a study published last month, the researchers used journal entries to draw a link between the proportion of non-straight edges in an image and thoughts relating to the themes of “nature” and “spiritual and life journey.”

All of this gets a bit esoteric, of course. But it was on my mind a few days ago, because my wife and I were visiting friends who lived in the downtown core, a few blocks from the 43rd-floor condo where we lived for year. As we walked back to the subway, my wife pointed down one of the busy streets and said “Remember when that used to be our running route?” There are a billion reasons I prefer running along the Humber, like cleaner air, softer surfaces, and no traffic. But I’ve always felt there was something more, too. I don’t really need to know exactly what that something is to appreciate it—but maybe having a better understanding of how we respond to nature will encourage us to take it more seriously, to ensure that we preserve wild spaces even within cities, and to make the time to visit them regularly.

My new book, Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance, with a foreword by Malcolm Gladwell, is now available. For more, join me on Twitter and Facebook, and sign up for the Sweat Science email newsletter.