Surround yourself with trees, and your heart will thank you for it!

We tend to surround ourselves with what brings us comfort.  It might be your favorite music, your favorite color, your favorite art, and even your favorite pillow or type of sheets when you go to bed.  What if your source of comfort actually made you healthy?  Where you live and what you do with your property is an important choice that can affect your heart health.

We’ve been told for some time that plants have psychological and physical benefits–just look at this page of studies!  A new study (2021) correlates the proximity of living near trees, to arterial stiffness.  According to a 2010 textbook, “Arterial stiffness describes the rigidity of the arterial wall. In the last decade, there has been increasing interest in the potential role of arterial stiffening in the development of cardiovascular disease in adults.”  In addition, the 2015 book Early Vascular Aging states, “Arterial stiffness is a hallmark of arterial aging. As with all other organ systems, changes in the vascular system are induced over time.”  This is very important, because cardiovascular disease (CVD) is the leading cause of death worldwide.  Although many associate CVD with genetics, “recent estimates suggest that up to 70%–80% of CVD burden could be attributed to non-genetic environmental factors, such as lifestyle choices, socioeconomic status, air pollution, lack of surrounding greenness (2), and residential characteristics (2018 study). Indeed, emerging evidence has shown that living in greener areas results in improved health and is associated with lower mortality (2016 study on mortality of women, 2016 study on green spaces and mortality), and reduced CVD risk (2019 study, 2012 study).”

How does the “proximity to greenness” cause these positive effects?  Is it because vegetation promotes exercise or a healthier lifestyle?  Or because it reduces stress?  Trees do have the ability to filter and block particulate matter, and it has been shown that people living in greener areas were exposed to lower levels of volatile organic compounds (2020 study).The 2021 study focused on reduction of pollution, particularly ozone and PM, due to plants and trees in specific radii around the home, and the effect of the reduced pollution on the participants’ arterial data.

What is proximity to greenness?  The study used satellite-derived normalized difference vegetation index (NDVI) for a 200-m and 1-km radius around each participant’s home; the 200 m range was directly around the home, while the 1 km radius indicated walking distance.  Data on ambient levels of pollutant concentrations were retrieved from regional EPA-validated monitoring stations in the Louisville, KY region, that report daily pollutant levels.  The data included PM2.5, PM10 and ozone. 

Here are some specific results: 

• At smaller radii (200 m) buffer around the home, inverse associations between standard deviation of NDVI and augmentation pressure, aortic pulse pressure, and aortic systolic pressure were observed (as greenness goes up, arterial stiffness goes down). 
• Significant positive associations between several arterial stiffness metrics and pollutants in low greenness areas were observed, whereas the association between pollutants and arterial stiffness measures was not significant in areas of high greenness (as greenness goes down, arterial stiffness goes up).
• Arterial stiffness was only associated with NDVI at the 200-m radius, but not the 1-km radius, giving support to the theory that because roadways are sources of pollutants, street trees within a 200-m radius around the individuals’ residence would be more relevant in blocking exposure to pollution. 
• It was shown that ozone, but not PM2.5, was significantly associated with higher augmentation index (increased arterial stiffness). This suggests that ozone-induced effects on arterial stiffness are independent of PM2.5 exposure and potentially stronger.
• In addition to modifying the effects of air pollution, proximity to greenness may improve cardiovascular health by decreasing mental stress. Exposure to natural outdoor environments has been found to be associated with better mental health and could facilitate stress reduction (2017 study), and neighborhood greenness is associated with lower levels of self-perceived stress and depression (2018 study), particularly in older adults. In our work, we have found that higher levels of residential greenness are inversely associated with urinary levels of the stress hormone—epinephrine (2018 study). Hence, it seems plausible that some of the effects of greenness on arterial stiffness may be mediated by a reduction in mental stress. 

How can we apply these findings to our own lives?  Since “greenness” is good for our bodies, plant as many trees and shrubs as possible, and encourage your neighbors to do so as well, by letting them know how good it is for them and the neighborhood.  The 200 meter radius is equivalent to 656 feet, which when converted to square feet (656 x 656) is equivalent to 2.3 acres.  That is a big green space that not many people own for their own property, but when spread out over a neighborhood or nearby park, it is certainly achievable.  If you live near a busy highway or road, definitely plant as much green area on the border of your property as you can. 

Some tree species are better than others at absorbing pollution, because as we’ve mentioned in other posts, some plants take in ground-level ozone, while other plants emit isoprene, a VOC that reacts with other atmospheric chemicals to create ozone. (Scientific American).  You definitely want the former type!   Here are some tips:

• A free online tool called i-Tree Species helps you to select the best plants depending on desired hardiness (after all, if the plant won’t live in your area it won’t do much good to introduce it), mature height and environmental factors such as air pollution removal and air temperature reduction, among other factors.
• In one recent study, Barbara Maher and colleagues at the University of Lancaster tested the ability of nine tree species to capture PM in wind-tunnel experiments. Silver birch, yew and elder trees were the most effective at capturing particles, and it was the hairs of their leaves that contributed to reduction rates of 79%, 71% and 70% respectively. (bbc.com)
• Conifers, such as pines and cypresses, are the best pollution filters, while London plane, silver maple and honey locust ranked above average too, according to Jun Yang, an urban ecologist at the Center for Earth System Science, Tsinghua University in Beijing. (bbc.com)
• If you have the opportunity to give input for city-wide greenery initiatives, be aware that taller species of trees can trap pollutants in areas, so sometimes shrubs are better when narrow streets are surrounded by tall buildings. 
• If you do have a large property or even a city park to design, remember to diversify the species so that certain pests or adverse conditions like too much or too little rain will not wipe out the whole property.  

In all, green spaces mean gold stars for your heart health, so it’s time to start seeing green!