Fact checked byKristen Dowd

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June 19, 2024
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Increased greenness, canopy cover may have protective measures in respiratory outcomes

Fact checked byKristen Dowd
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Key takeaways:

  • Green foliage and tree canopies can act preventatively against asthma and other respiratory disease.
  • Areas known to have high pollution exposure can benefit from increased greenness.

SAN DIEGO — Greenness and foliage may have protective measures when it comes to respiratory outcomes in Bay Area communities in California, according to a poster shown at the American Thoracic Society International Conference.

These Bay Area communities are known to have high levels of exposure through environmental and industrial pollutants, including freight rail, superhighways and industrial refineries, Andrew Nguyen, MPH, research data analyst at the School of Medicine, University of California, San Francisco, and colleagues wrote.

Cali
Freight rail, superhighways and industrial refineries contribute to elevated asthma rates in Richmond, California, but access to greenness and foliage may have protective associations with respiratory outcomes. Image: Adobe Stock

The study was conducted in Richmond, California, an area surrounded by several sources of air pollutants. Researchers aimed to find out whether residing near greenness can provide protective measures that could mitigate negative respiratory health outcomes through the absorption and blockage of particles by using a variety of measures to estimate reduction of negative outcomes from fine particulate matter (PM2.5) in the Bay Area, particularly in Richmond.

Methods

Researchers used 1,539 census tracts records in the Bay Area from 2011 to 2013 and 2015 to 2017 to estimate the burden of asthma-related ED visits (EDVs) as a function of PM2.5 using mixed-effects models. The models accounted for temporal trends and within-unit autocorrelation.

They found the number of census-tract specific PM2.5 attributable EDVs by comparing observed counts with modelled estimates with no PM2.5. They then estimated the associations between greenness and foliage (normalized difference vegetation indices, or NDVI) on EDVs at the census-tract level. Using equity and equality-based scenarios in a G-computation, they were able to predict the number of attributable EDVs avoided over the study period due to increased greenness and tree canopy cover.

Results

Modeling showed that higher levels of greenness and tree canopy cover had a negative association with risk for PM2.5 and attributable asthma-related EDVs. Out of 69,428 EDVs, there was an average of 1,230 EDVs avoided. Increasing modeling by 5% and 10% of NDVI showed 2.9% and 5.8% avoidance of EDVs. Increasing model tree canopy cover by 5% and 10% led to 1.7% and 3.5% of EDVs avoided.

Modeling a 30% increase in NDVI and tree canopy cover in the most socioeconomically vulnerable areas led to smaller reductions in EDVs (1.7% and 0.5%) but larger reductions in areas such as Richmond and Oakland.

Researchers noted that access to greenness and foliage in the environment may have protective associations with respiratory outcomes in areas that have high levels of environmental and industrial pollution, such as the Bay Area. They encourage further research to examine the mechanisms that allow this association to occur.