Growing evidence suggests that time spent in greenery is good for us
Need a quick mood boost that holds the promise of greater health and well-being?
A simple nature stroll may do the trick — and spending maximum time in or near greenery may make you healthier and more disease-resistant.
Recent studies bolster the presumed health benefits of spending time in greenery — no exercise is needed, all you need do is take a walk in the woods.
And if you’re an urban dweller, don’t fret — even strolling down a tree-lined sidewalk or through a public park “counts” as time in green space.
Research in this realm dates back a decade or more, and the evidence in favor of spending time in or near greenery keeps growing.
We’ll examine two recent evidence reviews, earlier Japanese studies of “forest bathing”, and an intriguing U.S. Forest Service study — then we’ll explore possible reasons why time spent in and around greenery would be beneficial.
Evidence review supported the value of “green time”
Last year, researchers from the University of San Francisco published a comprehensive 2017 review that encompass more than 60 studies — and its results support the benefits of time spent in green spaces (Hansen MM et al. 2017).
They selected studies that focused on the physical and psychological effects nature therapy or forest bathing, including heart rate, disease states, and the health of participants nervous and endocrine systems.
Encouragingly, they found significant credible evidence that exposure to nature reduces heart rate and blood pressure and increases relaxation — even when that exposure consisted of simply viewing videos of the forest or ocean.
Time spent in or looking at natural scenes also increased feelings of safety and calm — and benefited adults with depression and/or alcohol addiction.
New review further supports the health benefits of green spaces
Earlier this year, researchers from Britain’s University of East Anglia (UEA) published the results of their review of the existing evidence on this topic.
The study’s lead author — Caoimhe Twohig-Bennett, from UEA’s Norwich Medical School — explained the motivation behind their evidence review: “Spending time in nature certainly makes us feel healthier, but until now the impact on our long-term wellbeing hasn’t been fully understood.”
For the purposes of the study, the team defined “green space” as undeveloped, open areas full of natural vegetation, and these spaces included not only forests and fields, but also urban parks and even greenery along streets.
They set out to compare the health of people with little to no access to green spaces to that of people who spent the most time within greenery — or near it (Twohig-Bennett C et al. 2018).
The British team analyzed health and lifestyle data from more than 140 studies that involved close to 300 million people from 20 countries, including the U.S., the UK, France, Spain, Japan, Germany and Australia.
And the results of their analysis linked greater time spent near greenery — or spending substantial time in green spaces — to reduced risk of diabetes, heart disease, and premature death.
Better yet, greater exposure to greenery was linked to better overall health and to improved quality and quantity of sleep.
Dr. Twohig-Bennett, added this key point: “... one of the really interesting things we found is that exposure to greenspace significantly reduces people’s levels of salivary cortisol — a physiological marker of stress."
As study co-author Prof Andy Jones said, “... exposure to health-promoting environments is increasingly recognized as both preventing and helping treat disease. Our study shows that the size of these benefits can be enough to have a meaningful clinical impact.”
American-Canadian study suggests “green” and “blue” spaces benefit older adults
Three years ago, researchers from the Universities of Minnesota and British Columbia collaborated on a study in older adults.
They wanted to see whether seniors benefit from proximity and access to small green features such as a bench in a flower garden, or “blue” spaces that feature running or still water, such as a koi pond.
The researchers interviewed low-income adults ranging in age from 65-86 who lived in Vancouver, B.C. and had a range of chronic conditions and overall health (Finlay J et al. 2015).
And their results showed that natural environments reduced or prevented feelings of isolation, loneliness and boredom.
In addition, time near blue or green spaces boosted participants’ feelings of accomplishment and purpose.
Jessica Finlay, lead author of the study, expressed their findings this way: “We discovered how a relatively mundane experience, such as hearing the sound of water or a bee buzzing among flowers, can have a tremendous impact on overall health.”
As she said, “Accessibility to everyday green and blue spaces encourages seniors to simply get out the door. This in turn motivates them to be active physically, spiritually and socially, which can offset chronic illness, disability and isolation.”
Studies of “forest bathing” paved the research path
The Japanese practice of shinrin-yoku or “forest bathing” first appeared in the 1980s and is backed by a growing body of evidence that links it to numerous health benefits that.
Forest bathing isn’t about working out in nature — it’s simply walking in a forest and focusing on your natural surroundings.
Research suggests that forest bathing can reduce stress, lower blood pressure, boost immune health, and more.
Let’s examine three studies that blazed the trail of research in this realm.
Japanese research team conducted experiments during which subjects walked either in a wooded area or an urban environment, then switched environments (Park BJ et al. 2010).
Before and after each visit, researchers collected data looking at key indicators of stress: cortisol levels, pulse rate, blood pressure and changes in heart rate.
The results of that 2010 study show that forest environments promoted lower levels of cortisol, lower pulse rates, lower blood pressure, greater parasympathetic nerve activity, and lower sympathetic nerve activity than city environments.
In this study, Japanese researchers probed the immune-system effects of forest bathing (Qing Li 2010).
The participants were taken on a three-day trip to the forest, and scientists analyzed the levels of natural killer (NK) immune cells in volunteers’ blood after two days, three days, seven days, and 30 days.
Natural killer (NK) cells play a major role in your body’s immune system, specifically by protecting your body from virus-infected and cancerous cells.
The control group of adults went about their normal lies in urban areas, and their blood was also analyzed for the levels and activity of NK immune cells.
Blood analysis showed that NK levels in the forest group were significantly higher after just two days and remained higher than normal 30 days after the trip, suggesting that a monthly visit to the forest might provide a lasting immune benefit.
A Chinese study focused on how — compared to time spent in urban areas — forest bathing affects blood pressure, mood, and inflammation in older adults (Mao GX et al. 2012).
The participants took a seven-day trip to an evergreen forest, while the control group was sent to the city. The control group showed no significant changes, but the forest-bathers enjoyed significant improvements in blood pressure, inflammation levels, and cardiovascular health.
Loss of trees linked to adverse health outcomes
Just as spending more time in green spaces appears beneficial, loss of greenery may undermine human health.
The emerald ash borer is an insect pest that’s killed a hundred million trees across North America in recent years.
Researchers at the U.S. Forest Service wanted to see whether the massive of loss of trees to this insect had any effect on human health (Donovan GH et al. 2013).
They used statistical models to estimate the relationship between emerald ash borer presence and disease or death rates from 1990 to 2007 in 15 U.S. states — and they adjusted the results to account for a wide range of demographic factors known to affect the risk of death.
The Forest Service team was surprised to find substantial rises in the rates of cardiovascular and lower-respiratory-tract illness in counties that had lost many trees to the pest.
Further, the size of this link grew greater as the infestation progressed, especially in counties with above-average average household income.
Across the 15 states in the study, presence of the ash borer was linked to an additional 6,113 respiratory -related deaths, and 15,080 heart-related deaths.
As the Forest Service team wrote, “This finding adds to the growing evidence that the natural environment provides major public health benefits.”
Why would time around trees be beneficial?
There are at least three possible explanations for the physical and psychological benefits associated with time spent in or viewing nature.
First, we evolved in and became adapted to natural surroundings over hundreds of thousands of years, and our immersion in urban environments is very recent, brief episode.
Second, trees and other plants emit a wide range of essential oils and other compounds collectively called phytoncide, to repel germs and insects.
Examples include the sulfurous compounds in garlic (allicin and diallyl disulfide), and the terpenes in pine trees.
Interestingly, various phytoncide compounds are common components of traditional and modern medicine in Central and East Asia — possibly because phytoncides exert antioxidant and antimicrobial effects (Abe T et al. 2008).
Breathing air rich in phytoncide appears to boost immune system functions, and experiments in animals appear to confirm their benefits while excluding the placebo effect that plagues human studies.
A Japanese study found that exposure to phytoncide reduced stress responses in stroke-prone rats with high blood pressure (Kohei et al. 2004).
Likewise, a South Korean study found that a phytoncide from pine trees improved the health and bacterial make-up of weaning pigs (Zhang S et al. 2012).
As the Korean scientists wrote, “… phytoncide can elevate feed efficiency, nutrient digestibility, and improve the fecal Lactobacillus counts in weaning pigs. Our results indicated that the phytoncide could be used as a good antibiotics alternative in weaning pigs.”
Finally, compared with urban environments, forest and ocean environments abound in negative ions — with levels in in heavily wooded areas as high as double the levels found in in open and urban areas distant from trees.
Studies have shown that negative ions may benefit human health — which explains why it’s easy to find negative-ion generators on the Internet.
In contrast positive ions have been associated with several health problems — although research has yet to confirm or explain the apparent links between negative ions, positive ions, and human health and mood.
Two recent evidence reviews failed to find any substantial links between negative or positive ions and health in humans and animals (Alexander DD et al. 2013; Bailey WH et al. 2018).
However, the Chicago team behind one of those reviews did find that air especially rich in negative ions appear to alleviate depressed mood: “Negative air ionization was associated with lower depression scores particularly at the highest exposure level.” (Perez V et al. 2013)
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