Discovering the many health benefits of nature

Many people intuitively know that taking a walk in nature is beneficial, but significant research in recent years has confirmed this. Natural sights and sounds can reduce stress, improve mood, and improve overall mental health.

One of the best summaries of some of these benefits is the 2015 paper “How might contact with nature promote human health? Promising mechanisms and a possible central pathway” by Ming Kuo. These excerpts from Kuo discuss several ways nature improves health, with supplemental source links:

“The sights and sounds of nature also have important physiological impacts. Window views and images of nature reduce sympathetic nervous activity and increase parasympathetic activity (e.g., Gladwell et al., 2012; Brown et al., 2013), restore attention (e.g., Berto, 2005), and promote healing from surgery (Ulrich, 1984). Sounds of nature played over headphones increase parasympathetic activation (Alvarsson et al., 2010). These sympathetic and parasympathetic effects drive the immune system’s behavior (Kenney and Ganta, 2014), with long-term health consequences.

Didehydroepiandrosterone (DHEA) increases after a forest walk (Li et al., 2011); DHEA has cardio protective, anti-obesity, and anti-diabetic properties (Bjørnerem et al., 2004). Similarly, time in nature increases adiponectin (Li et al., 2011), which protects against atherosclerosis, among other things, and the immune system’s anti-cancer (so-called “Natural Killer,” or NK) cells and related factors. NK cells play important protective roles in cancer, viral infections, pregnancy, and other health outcomes (Orange and Ballas, 2006).

Chronically elevated blood glucose carries multiple health risks, including blindness, nerve damage, and kidney failure (Sheetz and King, 2002). The powerful effects of a walk in a forest on blood glucose are particularly striking.

Two 2-h forest walks on consecutive days increased the number and activity of anti-cancer NK cells by 50 and 56%, respectively, and activity remained significantly boosted even a month after returning to urban life — 23% higher than before the walks (Li, 2010). Moreover, extended time in a forest decreased inflammatory cytokines implicated in chronic disease by roughly one-half (Mao et al., 2012). Urban walks have no such effect.”

According to the American Psychological Association, “green spaces near schools promote cognitive development in children and green views near children’s homes promote self-control behaviors. Adults assigned to public housing units in neighborhoods with more green space showed better attentional functioning than those assigned to units with less access to natural environments. And experiments have found that being exposed to natural environments improves working memory, cognitive flexibility and attentional control.” APA also suggests that “children who lived in neighborhoods with more green space had a reduced risk of many psychiatric disorders later in life.”

Additionally, “contact with nature is associated with increases in happiness, subjective well-being, positive affect, positive social interactions and a sense of meaning and purpose in life, as well as decreases in mental distress.”

There’s even some evidence that time in nature can make people more cooperative and generous. Interactions with nature can positively influence behaviour, academic performance and social skills in children, something that could be reflected in school curricula (e.g., environmental experience components) and could have broader benefits, such as reducing bullying in schools.  

Another study found that “participants who listened to nature sounds like crickets chirping and waves crashing performed better on demanding cognitive tests than those who listened to urban sounds like traffic and the clatter of a busy café.”

There is also consistent evidence from birth cohort studies that higher greenness during pregnancy is positively associated with birth weight.

Nature and Forest Therapy is a burgeoning activity across the world. “Forest therapy is based on forest bathing, or shinrin-yoku, a Japanese practice that has garnered attention for its ability to immerse people into their natural environment. It helps people take a deep breath and rediscover our true essence, to remember our purpose and how we can serve the world. By immersing ourselves in nature and engaging our senses, we can reap the many benefits of forest therapy such as improved immune function, cardiovascular and respiratory health, and reduced stress and depression.”
​
“The results of studies performed on the physiological effects of Shinrin-yoku show that forest environments could lower concentrations of cortisol, lower pulse rate, lower blood pressure, increase parasympathetic nerve activity, and lower sympathetic nerve activity compared with city settings. The results of the physiological measurements suggest that Shinrin-yoku can aid in effectively relaxing the human body, and the psychological effects of forest areas have been correlated with the various physical environmental factors of forest. The studies of Shinrin-yoku provide valuable insights into the relationship between forests and human health.

Incorporating nature into cities has long been known to provide health benefits of improved air quality and reduce the urban heat island effect. There’s even evidence that natural landscapes in cities can help reduce crime rates.

“Comparing buildings with different levels of vegetation, those with high levels of vegetation recorded 52% fewer total crimes, 48% fewer property crimes, and 56% fewer violent crimes than buildings with low levels of vegetation. Even modest amounts of greenery were associated with lower crime rates.”

“These results suggest that vegetation is indeed related to criminal activity across the city, and that vegetation abundance is associated with lower crime rates for assault, robbery, and burglary. The association of vegetation with crime rates for these offense types remains even after accounting for the relationship of socioeconomic indicators of disadvantage, including poverty and educational attainment.”

Further, walks in forested, but not urban areas, reduce the levels of health risk factors, specifically inflammatory cytokines (Mao et al., 2012), and elevated blood glucose (Ohtsuka et al., 1998). Inflammatory cytokines are released by the immune system in response to threat, and have been implicated in diabetes, cardiovascular disease, and depression.

Tree-lined streets and small city parks can offer little bits of nature for urban residents. photo by Lance Brisbois

One other factors contributing to nature’s healing properties are the smells and ions associated with nature. “Many plants give off phytoncides — antimicrobial volatile organic compounds — which reduce blood pressure, alter autonomic activity, and boost immune functioning, among other effects.

The air in forested and mountainous areas, and near moving water, contains high concentrations of negative air ions, which reduce depression among other effects. These environments also contain mycobacterium vaccae, a microorganism that appears to boost immune functioning.” 

Being on or near water in nature also has many benefits, in what some call the “Blue Mind Theory.”

​Sun exposure, with some basic safety precautions (avoid sunburn and don’t look directly at the sun!) generally has many health benefits too. Getting outdoors and seeing sunlight first thing in the morning is one of the best ways to regulate circadian rhythms and develop healthy sleep patterns. Vitamin D is created by sunlight on the skin, and food and supplement sources of vitamin D are not nearly as bioavailable. More than 40% of Americans are estimated to have a Vitamin D deficiency.

Throughout the COVID-19 pandemic, outdoor activities were seen as much safer than indoor ones. Risks of spreading COVID and many other illnesses are significantly lower outdoors with fresh air and sunlight. Today, most people spend too much time indoors, inactive, and looking at blue-light screens.

Air quality is often significantly worse indoors compared to outdoors, with volatile organic compounds, mold, and particulate matter from things like paint, carpet, plastics, and other materials. Simply opening windows and adding indoor plants can help improve indoor air quality.

Another interesting affect of nature is the activity of viewing fractals. Fractals, or repeating patterns, are abundant in nature, such as in tree branches and snowflakes. Viewing fractals has been shown to reduce stress and help people heal more quickly.

examples of fractals in nature. Image source: https://medium.com/re-write/exploring-fractal-patterns-e161081f9723

Cardio and strength training can also be done outdoors combining the benefits of both. Instead of a treadmill, stationary bike, or stair-climbing machine, try hiking, biking, or jogging in a local park.

Getting out in nature with friends and family can provide much-needed human connectedness and socialization in a culture of increasingly isolated and lonely individuals. Nature can also, on the other hand, provide people a way to get out and away from the stresses created by the hustle & bustle of modern life.

Time in nature often provides us with a sense of awe. “The physiological experience of awe – goosebumps, dropped jaws, caught breath – is wonderful in itself, but research suggests that regularly feeling wonder can have a range of benefits for our physical and mental wellbeing as well as increasing our compassion, generosity and critical thinking ability.”

With all of these benefits, it’s no surprise that some doctors are now prescribing time outdoors for a variety of physical & mental health ailments, including the Park Rx and Prescription Trails programs.

On a broader scale, populations with easy access to nature tend to be healthier. Iowa is the most physically-altered (least natural) state. It is likely not a coincidence, then, that Iowa has some of the least-healthy counties in the U.S., and the second-highest cancer rate. Integrating nature back into the landscape of Iowa could help us become healthier, happier, and safer.

County health rankings for Iowa. Source: https://www.countyhealthrankings.org/health-data/iowa?year=2024

Other links & resources on this topic:

• American Hiking Society - Hiking Trails in America: Pathways to Health
• HEALTH BENEFITS OF CONTACT WITH NATURE A Literature Review Prepared By Sara Perrins and Dr. Gregory Bratman of the University of Washington for the Recreation and Conservation Office.
• CDC Improving Public Health through Public Parks & Trails: Eight Common Measures
• Outdoor Recreation, Health, and Wellness: Understanding and Enhancing the Relationship
• Parks, Trails, and Health Workbook: A Tool for Planners, Parks & Recreation Professionals, and Health Practitioners
• Children & Nature Initiative