How Trees Make Us Healthier & Happier

You know that refreshed feeling you get after walking through a forest, a park, or even just a tree-lined street? Somewhere among the rustling leaves, your bad mood lifts away, and you feel calmer, clearer, and revitalized. It’s not just your imagination: being around trees is actually good for you, and we’ve got the science to prove it. 

Studies show that exposure to natural, green environments, and particularly trees, can have profound, measurable effects on our physical and mental health. Here are a few of the ways that trees make you healthier and happier.

1. Trees Clean and Cool the Air

If there’s one thing you already know about trees, it’s that they are the earth’s great air conditioners and purifiers. In fact, trees are what make the earth a human-friendly habitat. They produce the very oxygen you breathe, while cleansing CO2 and air pollutants from the atmosphere. One of the reasons you feel so good after walking through the trees is all of that fresh oxygen revitalizing every cell in your body.

Good air quality is increasingly hard to come by in our industrialized age. A startling 2018 report from the World Health Organization found that 90% of the world’s children are breathing toxic air, threatening their neurodevelopment and putting them at higher risk of asthma and cardiovascular problems later in life. Pregnant women who are exposed to polluted air are more likely to have premature, lower-weight babies.(1) 

But trees can help absorb those air toxins and reverse these troubling trends. One study found that, in 2010 alone, the trees in the U.S. removed 17.4 million tonnes of air pollution, helping to prevent 850 deaths and 670,000 cases of acute respiratory symptoms.(2) Studies show that when there are more trees nearby, child asthma rates are lower(3) and average birth weights are higher.(4) And when there are less trees, things get worse: in one region where a forest pest destroyed 100 million trees, there was a notable increase in mortality related to lower respiratory and cardiovascular illness.(5) 

By absorbing greenhouse gasses, as well as cooling the air through water evaporation, trees are also our best defense against climate change. We tend to think of climate change as a global problem, but it’s a local problem, too. Cities with less tree canopy coverage are vulnerable to the “urban heat island” effect, which can increase local temperatures by up to 15 degrees, according to a study by the Texas Tree Foundation. More people in the U.S. die from heat each year than from all other natural disasters combined, and climate change will only make things worse. A study by the NRDC predicts that by 2040, the U.S. will see 30,000 heat deaths a year. 

Hotter air also traps toxic air pollutants, exacerbating the poor local air quality and snowballing the urban heat island effect. But trees can help solve both these problems. The Texas Tree Foundation study concluded that planting 250,000 trees in Dallas could cool local temperatures enough to provide significant energy savings and health benefits for the city. If more cities did the same, those local benefits can also become global.

2. Trees Are Therapeutic

As the saying goes, “It’s impossible to walk in the woods and be in a bad mood at the same time.” Being among the trees has a natural restorative effect on the nervous system, relieving stress and lifting our spirits. In Japan, “forest bathing” has long been considered a form of therapy, and recent studies bear this out. Forest bathers show a significant increase in positive emotions and parasympathetic nervous system activity, with significant decreases in stress indicators such as negative emotions, blood cortisol levels, blood pressure, heart rate, and sympathetic nervous system activity.(6,7,8)

What is it about being in the trees that’s so relaxing and uplifting? One of the best working theories is known as attention restoration theory.” The idea is that, while urban environments grab our attention with direct stimulation, natural environments engage our attention in a more relaxed, effortless way, lulling the mind into a meditative state. Brain scans seem to confirm this: EEG recordings show that people’s brains are less frustrated and more engaged and meditative while walking through natural, green environments, compared to urban environments.(9)

Humans evolved within green spaces, after all, our brains and nervous systems fine-tuned to the natural world. The biophilia hypothesis proposed by Harvard evolutionary biologist Edward O. Wilson suggests that this may have left us with an innate craving for nature. When we touch base with the natural world, we are soothed and comforted, as if restored to our native settings. 

These stress-relieving effects have profound implications not just for individuals, but for whole communities. Studies show that communities with access to more green space are less stressed and show less fear and aggressive behavior.(10,11) This translates into happier, more peaceful neighborhoods. Studies in Chicago,(12) Baltimore,(13) and New Haven(14) have shown that just a 10% increase in tree coverage is correlated with a 10-15% reduction in crime -- even after controlling for other influential factors, such as socioeconomic status, poverty, unemployment, and education. 

3. Trees Help Us Think

One of the benefits of the “attention restoration” effect is that it helps clear your head and refresh your thinking. The same way your computer works better after closing all of your tabs and rebooting, your mind works better after it’s had a meditative rest. Studies by psychology professor Marc Berman show that a walk through the park can improve attention and memory.(15) The results are even stronger for people with depression.(16)

This effect also has profound implications for attention and learning in children. The term “nature deficit disorder” was coined to describe the human costs of alienation from nature as our culture moves increasingly indoors. Drawing on the growing body of research that shows the importance of nature exposure for mental health, the idea links nature deprivation with attention, learning, and behavior problems in children.

Although nature deficit disorder isn’t a medical term, there is plenty of research to show that kids think better when they are exposed to green, natural environments. Studies have shown that children with attention deficit disorder focus better after walking through the park.(17,18) Another study showed that high school students performed better on tests and had better goals and behavior when their school environment included more trees.(19)

4. Trees Boost Disease-Resistance

We already know that trees support our long-term health by improving air quality and reducing stress. Long-term exposure to pollutants and chronic stress are both linked with eventual heart health problems. So it shouldn’t be too surprising that exposure to more trees is linked with fewer cases and better outcomes for cardio-metabolic conditions, including heart disease, stroke, diabetes, and hypertension.(5,20,21,22) One study found that having just 10 more trees per city block was linked with better self-rated health in ways “comparable to an increase in annual income of $10,000, or being 7 years younger.”

What might be more surprising is that trees have also been shown to boost immune function. Research on forest bathers shows that spending time in the trees increases disease-fighting natural killer cells and anti-cancer proteins in the blood.(23,24) Researchers are still exploring how this happens, but one possible mechanism is the phytoncides, or wood essential oils released by trees. At least two studies have found that these phytoncides enhance natural killer cell activity, in part by decreasing stress hormones.(25,26) These immune-boosting effects lasted more than a week after forest exposure.

At Naturelo, we’ve always appreciated the healing power of nature. That’s why we support the organization One Tree Planted, dedicated to planting more trees around the world. Every time you buy Naturelo supplements, you can feel good knowing that you’re helping us make the world a little greener, healthier, and happier by planting more trees. Nature gives us so much -- the least we can do is give back.

References:

1. “Air pollution and child health: Prescribing clean air.” World Health Organization, 2018.

2. Nowak, D. J., et al. “Tree and forest effects on air quality and human health in the United States.” Environmental Pollution, 2014.

3. Lovasi, Gina & Quinn, J.W. & Neckerman, K.M. & Perzanowski, Matthew & Rundle, Andrew. (2008). “Children living in areas with more trees have lower prevalence of asthma.” Journal of epidemiology and community health. 62. 647-9. 10.1136/jech.2007.071894.

4. Dzhambov, A.M., et al. “Association between residential greenness and birth weight: systematic review and meta-analysis.” Urban Forestry & Urban Greening, Vol. 13 Iss. 4, 2014.

5.  Donovan GH, Butry DT, Michael YL, et al. “The relationship between trees and human health: evidence from the spread of the emerald ash borer.Am J Prev Med. 2013;44(2):139-145. doi:10.1016/j.amepre.2012.09.066

6. Lee, J., Park, B.-J., Tsunetsugu, Y., Ohra, T., Kagawa, T., Miyazaki, Y. (2011). “Effect of Forest Bathing on Physiological and Psychological Responses in Young Japanese Male Subjects.” Public Health. 125(2): 93-100.

7. Park, B.-J., Tsunetsugu, Y., Kasetani, T., Kagawa, T., Miyazaki, Y. (2010).” The Physiological Effects of Shinrin-Yoku (Taking in the Forest Atmosphere or Forest Bathing): Evidence from Field Experiments in 24 Forests Across Japan.” Environmental Health and Preventative Medicine. 15(1):18-26.

8. Lee, J., Park, B.-J., Tsunetsugu, Y., Kagawa, T., Miyazaki, Y. (2009). “Restorative Effects of Viewing Real Forest Landscapes, Based on a Comparison with Urban Landscapes.” Scandinavian Journal of Forest Research. 24(3): 227-234.

9. Aspinall, P., Mavros, P., Coyne, R., Roe, J. (2012). “The Urban Brain: Analyzing Outdoor Physical Activity with Mobile EEG.” British Journal of Sports Medicine.

10. Thompson, C. W., Roe, J., Aspinall, P., Mitchell, R., Clow, A., Miller, D. (2012) “More Green Space is Linked to Less Stress in Deprived Communities: Evidence from Salivary Cortisol Patterns.” Landscape and Urban Planning. 105(3): 221-229.

11. Kuo, F. E., & Sullivan, W. C. (2001). “Environment and Crime in the Inner City: Does Vegetation Reduce Crime?Environment and Behavior, 33(3), 343–367. https://doi.org/10.1177/0013916501333002

12. Schusker, T., et al. “Research note: Examining the relationship between tree canopy, parks and crime in Chicago.” Landscape and Urban Planning, Vol 170, Feb 2018.

13. Troy, Austin & Grove, Morgan & O'Neil-Dunne, Jarlath. (2012). “The relationship between tree canopy and crime rates across an urban-rural gradient in the great Baltimore region.” Landscape and Urban Planning. 106. 262-270. 10.1016/j.landurbplan.2012.03.010.

14. Gilstad-Hayden, K., et al. “Research note: Greater tree canopy cover is associated with lower rates of both violent and property crime in New Haven CT.” Landscape and Urban Planning, Vol 143, Nov 2015.

15. Berman MG, Jonides J, Kaplan S. “The cognitive benefits of interacting with nature.” Psychol Sci. 2008;19(12):1207-1212. doi:10.1111/j.1467-9280.2008.02225.x

16. Berman, Marc G et al. “Interacting with nature improves cognition and affect for individuals with depression.Journal of affective disorders vol. 140,3 (2012): 300-5. doi:10.1016/j.jad.2012.03.012

17. Kuo, Frances E, and Andrea Faber Taylor. “A potential natural treatment for attention-deficit/hyperactivity disorder: evidence from a national study.” American journal of public health vol. 94,9 (2004): 1580-6. doi:10.2105/ajph.94.9.1580

18. Faber Taylor, A., & Kuo, F. E. (2009). “Children With Attention Deficits Concentrate Better After Walk in the Park.” Journal of Attention Disorders, 12(5), 402–409. https://doi.org/10.1177/1087054708323000

19. Matsuoka, R.H., (2010). “Student performance and high school landscapes: Examining the links.” Landscape and Urban Planning, 97(4), 273-282.

20. Kardan, O., Gozdyra, P., Misic, B. et al. “Neighborhood greenspace and health in a large urban center.” Sci Rep 5, 11610 (2015). https://doi.org/10.1038/srep11610

21.  Ohtsuka, Y., Yabunaka, N., Takayama, S. (1998). “Shinrin-Yoku (Forest-Air Bathing and Walking) Effectively Decreases Blood Glucose Levels in Diabetic Patients.” International Journal of Biometeorology. 41(3):125-7.

22. Mao G.X., Cao, Y.B., Lan, X.G., He, Z.H., Chen, Z.M., Wang, Y.Z., Hu, X.L., Lv, Y.D., Wang, G.F., Yan, J. (2012). “Therapeutic Effect of Forest Bathing on Human Hypertension in the Elderly.” Journal of Cardiology. 60:495-502.

23.  Li, Qing. “Effect of forest bathing trips on human immune function.Environmental health and preventive medicine vol. 15,1 (2010): 9-17. doi:10.1007/s12199-008-0068-3

24. Li Q, Morimoto K, Nakadai A, et al. “Forest bathing enhances human natural killer activity and expression of anti-cancer proteins.” Int J Immunopathol Pharmacol. 2007;20(2 Suppl 2):3-8. doi:10.1177/03946320070200S202

25. Li Q, Kobayashi M, Wakayama Y, et al. “Effect of phytoncide from trees on human natural killer cell function.” Int J Immunopathol Pharmacol. 2009;22(4):951-959. doi:10.1177/039463200902200410

26. Li Q, Nakadai A, Matsushima H, et al. “Phytoncides (wood essential oils) induce human natural killer cell activity.” Immunopharmacol Immunotoxicol. 2006;28(2):319-333. doi:10.1080/08923970600809439