Most people like being surrounded by nature. Even if it’s just a walk through a suburban city park or puttering about in a backyard garden, we’re drawn to green spaces filled with grass, trees, and leafy vegetation. They make us feel better. But the way we describe the effects of green space is all very amorphous and abstract and general, isn’t it? We “feel good” sitting on the grass. “It’s nice” to take a walk along a forest path. The office “doesn’t feel right” without a potted plant on the desk. Those sorts of benefits are great on a subjective level for the people experiencing them, but they aren’t very persuasive to others. If you want your ambivalent spouse to help grow the big garden you’ve always wanted, or your skeptical friends to start going on hikes with you, more specific and measurable reasons might be just the ticket.
So let’s dig deeper. Let’s explore the specific ways in which green spaces improve our lives:
A Japanese therapy called “forest bathing” involves spending deliberate time in nature (usually forests, hence the name) and actually boosts immune function. Natural killer cells are critical for proper function of the innate immune system; one of their most important functions is to eliminate tumors. And just a single day trip to a forest park can increase NK cell number and activity, as well as upregulate anti-cancer proteins, for up to a full week. In every forest bathing study, in fact, participants enjoy this increased natural killer cell (NK cell) activity and anti-cancer protein function.
If I’m ever stressed out and nothing’s helping, I’ll head out to the hills for a quick hike. Not a long one, not a grueling one. Just a quick jaunt to nature. Almost invariably, it works. I’m able to reset my stress response, get a handle on my sympathetic nervous system, and calmly address the source of the stress. So it’s no surprise that neighborhood green spaces are associated with healthier cortisol levels in deprived urban communities in Scotland and forest bathing therapy has been used to lower cortisol levels.
We tend to focus on physical health, but mental health (which isn’t really separate from physical health) is arguably more reliant on regular exposure to green space. Among both rural and urban Wisconsin residents, high levels of neighborhood green space were consistently linked to lower levels of anxiety, depression, and stress. And in case you’re thinking of moving, consider that people who move to “greener” urban neighborhoods enjoy improved mental health in the subsequent years than people who move to “less green” urban areas.
A week-long evergreen forest retreat reduced hypertension in elderly Japanese, while a control group taking a similar retreat in the city experienced no benefits to blood pressure. Heck, even in 10 year old kids living in urban areas, low levels of nearby green space were associated with higher blood pressure. No one’s blood pressure is immune to the lack of green space, and kids might even be more susceptible.
Now, this could very well merely be a correlation. But the presence of green space is fairly often linked to reductions in all-cause and stroke mortality. In a cohort of 575,000 urban Ontario residents aged 35 and older, for example, living near greenery reduced mortality. Same for ischemic stroke survivors and North Floridians.
In a recent study out of the Netherlands, proximity to urban green space was associated with improvements in both longevity and healthy longevity. So not only were people living longer, they were living longer and more healthfully: compression of morbidity. Controlling for income level did not alter the effect.
People enjoy working out in nature. They prefer to walk through a park to along a boring suburban street. They’d rather hike than slog on a treadmill. Tabata kettlebell swings are somehow more tolerable when done in fresh air with trees overhead and grass underfoot. The closer you are to a green space, the more likely you are to be physically active. Better still, green spaces promote the precise type of physical activity we so desperately lack these days: walking.
Exercise isn’t just good for the body, but also the mind; we often forget this. A 2011 meta-analysis broke down the psychological benefits of outdoor workouts. Compared to indoor workouts, outdoor workouts resulted in greater revitalization, increased energy, and more positive engagement, along with less depression, anger, confusion, and tension.
That’s an attractive assumption to make, but even though physical activity is consistently higher in greener neighborhoods, adjusting for this only slightly attenuates the relationship between green space and health. It’s not just the physical activity. It’s not even mostly the physical activity.
Diabetics who go on forest bathing trips enjoy lower blood sugar and improved HbA1c. And in Australians, living near green space was independently associated with a lower risk of type 2 diabetes. Not even controlling for demographics, income level, diet, activity level, culture, or health eliminated the link.
When you go camping, your sleep typically improves and instead of staying up past midnight, you might find yourself nodding off shortly after dark and waking up refreshed like never before. According to the conventional Primal explanation, the lack of artificial lighting is allowing your natural circadian rhythm to dictate your sleep habits. That’s certainly a huge part of it, but what if the presence of green vegetation is also playing a role? A recent study found evidence of such an effect, with urban dwellers living near green spaces reporting healthier sleep habits.
Exposure to green space engages our involuntary attention, the kind of soft focus where we’re seeing, hearing, and smelling sensory data without devoting huge amounts of brain power to it. This restores our voluntary attention, the kind of hard focus we require to concentrate on work-related tasks and be productive. Even brief exposure to pictures of nature scenes restores our attentional capacity – our ability to concentrate on a given task without deviating or becoming sidetracked.
Kids already know it. You set one down in a forest or park and they know exactly what to do. They’re running, jumping, climbing trees, digging for bugs, getting dirty, collecting leaves, inventing games, and sporting the biggest smiles you’ll ever see. So that’s reason enough to give children ample and regular (daily) access to green space. But there are also proven, measurable physiological and mental benefits for them, including: increased test scores in “nature-smart” kids; enhanced learning when curriculum is nature-based; reduced impact of ADHD; enhancement of self-discipline and self-control; improved cognitive function and concentration; and stress amelioration in highly-stressed kids. Kids with poor access to outdoor space are also more likely to have behavior problems. Powerful stuff, eh?
I’m not talking about human infants spawning from the roots of an old oak tree like something out of Celtic folklore. I refer to the findings of a recent study from Vancouver (hat tip to reader Wenchypoo for alerting me to it). Pregnant women in neighborhoods with ample amounts of grass, trees, and leafy vegetation gave birth to healthier babies than women in neighborhoods with less greenery. Even after researchers controlled for variables that also affect health at birth like neighborhood walkability, air and noise pollution, and income level, the association held firm. This study doesn’t confirm causality, but it’s certainly suggestive. And another study supports it, finding that urban green space was linked to lower rates of neonatal mortality.
This is a huge one that might explain the previous benefit to pregnant mothers and their babies. Grass, trees, and plants of all kinds reduce air pollution, so when you live in an area with ample green space – even an urban environment generating lots of pollution – you can breathe easier. In one recent study, researchers found that the more green space in and around a pregnant woman’s home, the lower her exposure to and inhalation of airborne pollution particulates.
While a lot of the benefits of green space are passive – you can just “be” and accrue positive effects to your health and well-being simply by being near vegetative growth – the active pursuit of experiences in nature provides further benefits. For instance, one study found that the mental health benefits associated with green space exposure were more evident in adults who were physically active in those spaces. Having a great park near your house doesn’t do much for you if you never walk through it.
So, how does this all happen? What’s so great about green space? I’ll give my little pet theory. See what you think about it.
We often forget that plants are alive. I mean, we cursorily acknowledge that they’re living, that they take in nutrients and grow and die, but we mostly think of them as passive, inanimate objects. Emerging evidence shows that plants are much more than that. They react to their surroundings. They communicate with each other using volatile airborne compounds to discuss incoming attacks from herbivores. They can “hear.” They sense gravity, and when an object is in the path of their growth can change that path to go around. They feel a sort of pain. They wield a sort of intelligence. Is it the same kind as human pain or human intelligence? No, but it’s there. They don’t have to be Tolkienesque Ents to have agency.
My wild guess is that humans can subconsciously eavesdrop on plant communication. We already know that humans can pick up on a tomato plant’s nutrient content by “listening to” its flavor-related volatile compounds. And when we’re exposed to the airborne phytoncides (wood essential oils/volatile compounds) released by trees, we enjoy increased immune function and lower stress. If you’ve ever walked through the rain forests of Washington state, for example, or the jungles of Thailand, you’ll know what I mean: you feel it. The place is alive and full of conversation. It’s in another language, and like visiting a busy marketplace in another country, you can’t quite make out the specifics, but you get the gist of what’s going on and you’re glad to have witnessed it.
That plant speak, those volatile airborne compounds, that’s a cue for our bodies. It’s the signal that we’re home, in good hands, in a good place amongst the greenery.
I know what a lot of you are thinking: correlation doesn’t necessarily equal causation. That’s true, and I’ve certainly said the same thing many times over on this blog. But there’s a difference with green space. Giving up red meat based on some correlative evidence is risky because red meat is a highly nutritious food, and besides, there’s lots of counter-evidence showing how healthy it can be. Exposing yourself to green spaces, taking walks in the park, going for hikes in the forest, planning a camping trip – these aren’t risky. These are fun activities and behaviors that you were probably going to do anyway. Even if there weren’t any established health benefits to green space, I’d still go for weekly hikes. I’d still camp with my family. I’d still go snowboarding every winter. I’d still walk barefoot in the cool dewy grass in my yard every morning.
What about you? How do you currently (or plan to) incorporate green spaces into your life?
Thanks for reading, all.
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