Exposure to vegetation and mortality rates in women

Women live longer in areas with more green vegetation, according to new research funded by the National Institute of Environmental Health Sciences. 

The study, published online on April 14, 2016 in the journal Environmental Health Perspectives claims that women with the highest levels of vegetation, or greenness, near their homes, appear to have a 12 percent lower death rate compared to women with the lowest levels of vegetation near their homes.

It also suggests several mechanisms that might be at play in the link between greenness and mortality rates. 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.

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. This study, conducted by scientists at Harvard T.H. Chan School of Public Health and Brigham and Women’s Hospital in Boston, examined greenness around the homes of 108,630 women in the long-term Nurses’ Health Study. The researchers mapped home locations and used high resolution satellite imagery to determine the level of vegetation within 250 meters and 1,250 meters of homes. They then followed the women from 2000 to 2008, tracking changes in vegetation and participant deaths. During the study, 8,604 deaths occurred.

The scientists also looked at characteristics that can otherwise contribute to mortality risk, such as age, race, ethnicity, smoking, and socioeconomic status. This enabled them to be more confident that vegetation plays a role in reduced mortality, rather than these factors. If participants moved or the vegetation near their homes changed during the study, the scientists took those changes into account in their study.

They consistently found lower mortality rates in women as levels of trees and plants increased around their homes. This trend was seen for separate causes of death, as well as when all causes were combined. When researchers compared women in the areas with highest greenness to women in the lowest, they found a 41 percent lower death rate for kidney disease, 34 percent lower death rate for respiratory disease, and 13 percent lower death rate for cancer in the greenest areas.

"We were surprised to observe such strong associations between increased exposure to greenness and lower mortality rates," said Peter James, of the Harvard T.H. Chan School of Public Health's Department of Epidemiology, who co-authored the study. "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."

"We know that planting vegetation can help the environment by reducing wastewater loads, sequestering carbon, and mitigating the effects of climate change," James concluded. "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."

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