Over an eight-year period, there were 12 per cent fewer deaths among women who lived in the greenest surroundings than among those who lived in the least green areas, according to the study published in the journal Environmental Health Perspectives.
Improved mental health, measured through lower levels of depression, was estimated to explain nearly 30 per cent of the benefit from living around greenery.
"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 apparent benefit from high levels of vegetation seems to be connected with improved mental health."
When the researchers looked at specific causes of death among the study participants, they found that associations between more greenery and fewer deaths were strongest for respiratory disease-related deaths and cancer deaths.
Women in the greenest areas had a 34 per cent lower rate of respiratory disease-related mortality and a 13 per cent lower rate of cancer mortality compared with those with the least green environments.
Those findings are consistent with the idea that greenery buffers air pollution and noise and provides 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 possible co-benefit—improving health—that presents planners, landscape architects, and policy makers with an potential tool to grow healthier places," said James.
Previous studies have suggested that exposure to vegetation was related to lower mortality rates, but those studies were felt to be limited in scope, and some had contradictory findings. The new study is the first in the United States to take a nationwide look at the link between greenness and mortality rates over a period of several years.
The study incorporated data on 108,630 women enrolled in the Nurses’ Health Study across the country in 2000-2008. Researchers accounted for other mortality risk factors, such as age, socioeconomic status, race and ethnicity, and smoking.
Researchers mapped home locations and used high-resolution satellite imagery to determine the level of vegetation within 250m and 1,250m of homes. They then followed the women between the years 2000 to 2008, tracking changes in vegetation and participant deaths. During the study, 8,604 of the women died.
The study was funded by the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health.