Abstract
Enhanced immune functioning in response to biodiversity may explain potential health benefits from exposure to green space. Using unique data on urban forest biodiversity at the zip code level for California measured from 2014 to 2019 we test whether greater diversity of street trees is associated with reduced death from cardiovascular disease. We find that urban forests with greater biodiversity measured via the Shannon Index at the genus level are associated with a lower mortality rate for heart disease and stroke. Our estimates imply that increasing the Shannon Index by one standard deviation (0.64) is associated with a decrease in the mortality rate of 21.4 per 100,000 individuals for heart disease or 13% and 7.7 per 100,000 individuals for stroke or 16%. Our estimates remain robust across several sensitivity checks. A policy simulation for tree planting in Los Angeles based on our estimates suggests that if these relationships were causal, investment in planting for a more biodiverse set of street trees would be a cost-effective way to reduce mortality related to cardiovascular disease in urban areas.
Highlights
Cardiovascular diseases, including heart disease, stroke, and hypertensive disease, are among the most preventable causes of death in the U.S and worldwide [1,2,3] and cost the U.S $199 billion in health care costs and $131 billion in lost job productivity annually [4]
Our results begin with a graphical assessment of how differences in urban forest biodiversity correlate with heart disease and stroke mortality rates
What is the shape of the raw relationship between urban forest diversity and mortality for heart disease and stroke? Fig 3 shows binned scatter plots of mortality rate per 100,000 people against the zip code’s Shannon Index
Summary
Cardiovascular diseases, including heart disease, stroke, and hypertensive disease, are among the most preventable causes of death in the U.S and worldwide [1,2,3] and cost the U.S $199 billion in health care costs and $131 billion in lost job productivity annually [4]. Prescription drug treatment of cardiovascular disease has improved, shifting the policy focus to prevention [3]. Cost-effective ways to prevent cardiovascular may be situated outside traditional health care systems. Though they have existed in principle since at least the 19th century, “green prescriptions,” or nature-based health interventions, are garnering attention and may help prevent cardiovascular disease [5]. A short walk through a forest lowers blood pressure [6] and living in greener areas is associated with a reduced risk of cardiovascular diseases [7].
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