Harvard T.H. Chan School of Public Health
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| Photo by Will Collette |
The study found
that women who lived in the greenest surroundings had a 12% lower overall mortality
rate than those living in homes in the least green areas.
The study suggests several mechanisms that might be at play in
the link between greenness and mortality.
Improved mental health, measured
through lower levels of depression, was estimated to explain nearly 30% of the
benefit from living around greater vegetation. Increased opportunities for
social engagement, higher physical activity, and lower exposure to air
pollution may also play an important role, the authors said.
"We were surprised to observe such strong associations
between increased exposure to greenness and lower mortality rates," said
Peter James, research associate in the Harvard Chan School Department of
Epidemiology. "We were even more surprised to find evidence that a large
proportion of the benefit from high levels of vegetation seems to be connected
with improved mental health."
Previous studies have suggested that exposure to vegetation was
related to lower mortality rates, but those studies were limited in scope, and
some had contradictory findings. The new study is the first to take a
nationwide look at the link between greenness and mortality over a period of
several years.
The study incorporated data on 108,630 women enrolled in the
Nurses' Health Study across the United States in 2000-2008.
The researchers
compared the participants' risk of mortality with the level of vegetation
surrounding their homes, which was calculated using satellite imagery from
different seasons and from different years.
The researchers accounted for other
mortality risk factors, such as age, socioeconomic status, race and ethnicity,
and smoking behaviors.
When the researchers looked at specific causes of death among
the study participants, they found that associations between higher amounts of
greenness and lower mortality were strongest for respiratory-disease and cancer
mortality.
Women living in areas with the most vegetation had a 34% lower rate
of respiratory disease-related mortality and a 13% lower rate of cancer
mortality compared with those with the least vegetation around their homes.
These more specific findings were consistent with some of the proposed benefits
of greener areas, including that they may buffer air pollution and noise
exposures and provide opportunities for physical activity.
"We know that planting vegetation can help the environment
by reducing wastewater loads, sequestering carbon, and mitigating the effects
of climate change. Our new findings suggest a potential co-benefit--improving
health--that presents planners, landscape architects, and policy makers with an
actionable tool to grow healthier places," said James.