Moving about the world is an essential part of the experience of being human.

Movement, and most especially lots of regular walking, is good—indeed, great—for body and brain. I want to go far beyond these simple and relatively uncontroversial contentions and investigate the potential wider benefits of walking—to ask how walking affects mood, mental health,and brain function.Regular walkers (myself included) claim that, deprived of the opportunity to walk for even a few days, we feel sluggish and tired and often a little bit down and that the self-administered cure is simple—to go out for a good walk. Thrillingly, there is now an emerging body of science that supports this anecdotal feelingand indicates that walking, especially in regular doses, often in nature, does actually improve how we feel. Think of all those blustery, rainy long walks that at the time might have felt arduous but at the end left you feeling elated. A good walk boosts how you feel and much more besides.

Hippocrates famously claimed that “walking is the best medicine.” Yet in our modern world, most of us spend all day indoors sitting down, which can have terrible consequences for our health and well-being. We spend less time outdoors than ever before. One major study in the U.S. showed that people spent 87 percent of their time in the artificial environment of offices, houses, shops,and other buildings.Some have even claimed (only somewhat exaggeratedly, in my view) that “sitting is the new smoking.” The sentiment behind this statement is straightforward: our bodies are built for regular movement and profit from it. Sedentary life is fundamentally unhealthy, leading to a decline in muscle volume and strength. Moreover, long periods of inactivity produce not dissimilar changes in the brain.

One interesting study recently found that lack of activity is even associated with a change in personality, and by this I mean a change for the worse. Overall, lower levels of physical activity were associated with changes in three of the “Big Five” factors of personality (these are openness, conscientiousness, extroversion, agreeableness, and neuroticism, easy to remember as OCEAN). Lower levels of physical activity were associated with declines in openness, extroversion,and agreeableness, suggesting a “detrimental” pattern of long-term personality change. Even minimal levels of activity were found to have a moderating effect on personality changes. 

Those individuals who were the most inactive were the ones most likely to show these negative personality changes. The pathway channeling such negative changes is unclear but is likely to involve the usual increases in illness and lack of well-being associated with prolonged inactivity, the limitations to activities of daily living associated with inactivity, changes in general cognitive function, and perhaps even changes in mood. Given what we know, it’s highly likely that a simple behavioral change—lots of walking—would be a viable way of reversing negative changes in personality resulting from a sessile life.

Standing leads to immediate changes in blood pressure, blood flow throughout the body, and the rate at which we consume energy and generate heat (our metabolic rate). Walking entrains changes across widespread brain and body systems, from the production of new molecules all the way to behavior. Regular up-tempo walking is a simple and straightforward way of exercising the heart, and this in turn provides great benefits for the head-heart axis, because about 20 percent of the output of the heart is directed toward the oxygen- and energy-hungry brain. Similar effects occur in the gut, which is also oxygen and energy hungry. The cure is right in front of us: to get up and walk.

Walking is one thing. Where we walk is quite another.

As more and more of us live in towns and cities, green spaces will only become more essential for our well-being. Building design, especially in northern and inclement regions, has, in some respects, historically taken account of this fact. Cloisters in university buildings, monasteries, and other locations allow people to walk outdoors while protected from the elements. Cloisters are sometimes referred to by their ritual and processional purpose—deambulatorium, obambulatorium, ambitus—the solemn Latin descriptors of the architectural elements of a monastery, all derived from the root ambio—“I walk in a circle.” They are also often called, appropriately enough, ambulatories. And of course, cloisters are usually constructed around a garden, ensuring a tamed element of nature is at the center of the walk. 

Walled gardens, dating from early times, are another way of bringing tamed nature within a building perimeter, yet allowing safe walking outdoors. In The Decameron, Giovanni Boccaccio writes of one such garden that“its outer edges and through the center ran wide walks as straight as arrows, covered with pergolas of vines which gave every sign of bearing plenty of grapes that year.... The sides of these walks were almost closed in with jasmine and red and white roses, so that it was possible to walk in the garden in a perfumed and delicious shade, untouched by the sun, not only in the early morning, but when the sun was high in the sky.” Modern building design incorporating cloisters, awnings, courtyards, and other features could make outdoor walking and exposure to nature easily achievable. Similarly, indoor walks around nature-bearing and displaying atriums could provide people with this feeling of connectedness to the natural world. Views from windows that provide glimpses of the sky and of trees could also enhance well-being markedly.

Yet this need in our lives for time outdoors and connection with nature is something we consistently seem to underestimate. This has been shown clearly by a study conducted in Ottawa. Ottawa is subject to weather extremes, with summer temperatures exceeding 86 degrees Fahrenheitand winter temperatures dropping below minus four degrees Fahrenheit. A substantial fraction of the large campus of Carleton University in Ottawa is connected via a system of extended underground tunnels to allow walking during weather extremes. Experimental psychologists examined the effect of people undertaking walks where they are exposed to nature versus walking in an enclosed environment by using this network of tunnels. They asked 150 participants to walk the same distance between two locations on the campus: either through an underground tunnel or outside along a riverbank in an urban space with plentiful trees, plants, and other features of the natural environment.

Prior to starting, participants were asked to state how they were currently feeling and then to estimate how they would feel after the 17-minute walk outdoors compared to the same walk indoors in the tunnels (using a rating scale). The results were clear: all participants substantially underestimated how the walk outdoors would make them feel relative to the walk indoors. The effect on the mood of the walk through the urban setting was compelling. There was an improvement in the individuals’ self-rated mood scores of about one-third on average, relative to individuals who undertook a walk indoors. (This study also demonstrates a persistent problem with how humans understand what affects our feelings: we are bad at forecasting how any activity is likely to make us feel—known as “affective forecasting.”)

But why does walkable green space matter so much for our well-being? What is it about nature that makes us feel better? Walking in the woods is something humans have done since time immemorial. Some cultures venerate this experience: the Japanese, for example, have the glorious tradition of forest bathing (shinrin-yoku): the practice of absorptive, enveloping walking in deep forests for the soothing properties of being connected to, and fully immersed in, the sights, sounds, and feel of nature. Forest bathing is an important manifestation of something that appears to be a universal in human experience—a veneration of nature as foundational to our lives, from early pantheistic theories, which imagine that spirits inhabit trees, woodland brooks, stones, and the like, through religions that worship the Earth Mother or deities (like the Inca goddess Pachamama) to the present-day idea of Gaia, scientist James Lovelock’s contention that we should regard the planet and all life on earth as a single, self-regulating ecosystem.

Certainly, many take the view that we need to care for nature and that nature as a source of well-being is central in our lives. There is also the great concern that human activity is having perhaps irreversible, and certainly malign, effects—from species hunted to extinction to contamination of water courses and seas with plastics, effluvia, and toxic materials to human effects on the climate of the planet itself. 

Scientific evidence also backs up our intuitive feeling that regular exposure to nature and the natural world has effects on human health and welfare which are positive, measurable, and enduring, and should be thought of as being akin to the provision of clean water, reliable electricity, public vaccination, or public hospitals. The evidence to support this can be found by measuring people’s stress levels before, during, and after their interactions with nature. The stress hormone cortisol is at the core of our “fight, flight, or freeze” response. Cortisol is released in response to the presence of stressors, with potentially positive and negative effects. In the short term, it is adaptive, mobilizing resources to help overcome stress. However, the chronic and sustained release of cortisol leads to a whole variety of problems, from the stiffening of our arteries and veins to malign effects on our mood and memory. One study in a very deprived area of Dundee, Scotland looked at how the amount of green space in a neighborhood might affect the levels of stress in residents of that neighborhood. This was measured both by perceived levels of stress (in other words, by self-report, how residents thought they were feeling) and by measuring levels of cortisol, which can be readily measured in both saliva and in the blood. The concentration of cortisol in our saliva varies across the course of the day, peaking in the early morning and decreasing toward the end of the day. People experiencing high levels of stress do not show this downward shift as nighttime approaches. In the Dundee study, researchers found that this diurnal decrease is absent, or at least relatively absent, in a deprived population who do not have regular access to and use of green spaces in their urban environment. Finding a correlation of this type is suggestive, and it matches to a similar body of evidence suggesting that exposure to nature may have important effects on human health and psychological well-being.

However, we should consider how people use the available green space. Do they visit it regularly? Do they use it for social walking, to walk the dog, to supervise children playing? This is where larger-scale studies are required and preferably studies that attempt to randomize treatment conditions so that some degree of causality can be figured out. Are your stress levels lower because you are exposed to nature, or is there some other factor? It may turn out, for example, that an extended experience of wild nature, involving long periods trekking or walking, might be a viable treatment for depression (at least in its milder forms) and perhaps even other stress- and anxiety-related conditions. Large-scale trials testing this idea have not been conducted, however.

Getting at whether or not exposure to nature has a causal effect in making you feel better—that exposure to nature generates a positive mood—requires studies that vary the dose of nature you are exposed to: Does it take a little, or a lot, and how often? The effects may be strong, weak, subtle, or indeed nonexistent; the risk of fooling yourself into thinking there is an effect when, in fact, there is none, is high.

“Attention restoration theory” is the idea that the natural environment has profound restorative effects on our well-being, and that the human experience of the natural world markedly assists in maintaining and fostering a strong sense of subjective well-being. According to psychologists, a natural environment should have three critical elements to be fully restorative: it should give you the sense of being removed from your normal life and surroundings, it should contain visual elements and sensory elements that are fascinating in some way, and it should be expansive—it should have some degree of extension. The increasing pressures of modern life tend to increase mental fatigue, but restorative experiences in nature might decrease it. This restorative effect is best mediated through a connection to natural environments, because they play an essential role in normal human functioning. 

In a study that involved 4,255 participants in the UK, researchers investigated this phenomenon of “restoration,” defined as feelings of calm, relaxation, revitalization, and refreshment as the result of visiting a natural environment in the previous week. The recalled restoration from a visit to nature was very high, with an average score of four on a scale of one to five. There was a hierarchy of locations, with coastal environments providing the greatest feeling of restoration, followed by the rural countryside, with urban green spaces coming in third. This hierarchy should perhaps be treated with some degree of caution, though—it is derived from an overall average, and many town parks were just as restorative as the open countryside. A majority of the highest socioeconomic group (53 percent) visited nature in the previous week, whereas only a minority (31 percent) of the lowest socioeconomic status group did so. The higher socioeconomic group, of course, will have, on average, better education, health status, access to nutrition, and the like.

What’s clear is that park design is a vital factor: the extent to which a park is usable, accessible, and facilitates different meaningful activities is the driver of park usage. The differences in feelings of restoration found between time spent in these various environments—the coast, the rural environment, urban parks—were not especially vast, and the study did not control for the activity that you could undertake in the differing areas. Urban green spaces can be used for tending to vegetables, as in an urban allotment; walking the dog, as in an urban park; or playing sports in urban sports fields. Easy access to nature is very important to individuals, families, social groups, and society at large, and well-designed urban green spaces can substitute for, or mimic in important ways, the effects of being in the countryside. Parks, for example, might allow wilderness areas supporting urban wildlife, insects, and birds, as opposed to carefully mown and tended grasses. Equally, the trails inscribed in these parks should, to the greatest extent possible, follow the undulations of the environment and of people’s “desire paths.”

It’s also been shown that the positive effect on mood after spending time in nature applies to a range of people of different ages, both male and female, across the globe. Perhaps more importantly, the impact of exposure to nature is comparable to other factors affecting individual happiness, including personal income levels, level of education, degree of religiosity, marital status, volunteering,and physical attractiveness.

It may not be possible to do much about one’s personal income, or indeed one’s perceived physical attractiveness, but getting out and going for a walk is something that we can all easily do. Because the evidence suggests that activity in nature has a long-lasting impact on our happiness and well-being, we should be encouraging our populations to regularly, habitually walk in nature, even if they only have access to city parks.

Excerpted from In Praise of Walking: A New Scientific Exploration, by Shane O’Mara. Copyright © 2019 by Shane O’Mara. With permission of the publisher, W. W. Norton & Company, Inc. All rights reserved.