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Being green might not be easy (just ask Kermit the Frog), but being surrounded by green may help people live longer. According to a study published recently in Environmental Health Perspectives, American women living closest to high levels of environmental vegetation or “greenness” enjoy a 12% lower rate of dying from non-accidental causes than women living in less green areas.
Women living with a high density of greenness “directly accessible” outside their home (within a 1,000-foot radius) were, according to the study, less likely to die from respiratory disease, cancer, and kidney disease than women who had to walk roughly three quarters of a mile to reach a similar density of greenness. Living close to greenness, especially for long periods of time, was associated with reduced exposure to air pollution, as well as greater physical and social activity and better mental health. The lower mortality rate was the same regardless of age, race, socio-economic or smoking status, and whether the women lived in urban or rural areas.
Researchers with the Harvard T.H. Chan School of Public Health and Brigham and Women’s Hospital used data from surveys sent to Nurses Health Study (NHS) participants. Established in 1976 with funding from the National Institutes of Health, the NHS began surveying more than 120,000 nurses every two years about oral contraceptive use, and expanded the surveys to include smoking, menopause, diet and nutrition, quality of life, cancer, and a variety of diseases. Nurses were selected for the long-term study because their medical training helped them answer complex questions about women’s health. (A Nurses Health Study II was started in 1989, and a third that includes both male and female health workers was launched in 2010.)
Entitled Exposure to Greenness and Mortality in a Nationwide Prospective Cohort Study of Women, the study combined NHS survey responses with images from the MODerate-resolution Imaging Spectroradiometer (MODIS) sensor on Terra, a NASA satellite that studies Earth’s land surface, oceans and atmosphere. One of MODIS’s tasks is to measure “vegetative density” – or levels of natural greenness – all over the globe.
Greenness is ranked according to the Normalized Difference Vegetation Index (NDVI), which measures how plants absorb and reflect light; the more infrared light that is reflected, the healthier the vegetation. NHS participants’ addresses were matched by longitude and latitude (called geocoding) to the level of greenness surrounding their homes, as determined by the NDVI.
The study analyzed non-accidental causes of death for the 8,600 NHS participants who died between 2000 and 2008, and looked for links to greenness exposure. According to the report, higher levels of greenness around each participant’s address were associated with lower rates of respiratory disease, kidney disease and cancer.
Reductions in respiratory and cancer deaths are attributed to the observation that greenness lessens air pollution exposure (plants can absorb pollutants) and encourages physical activity, both of which are associated with lower risks of these diseases; increased physical activity is associated with a lower risk for kidney disease as well. Higher exposure to greenness has been consistently linked to lower levels of stress, depression, and anxiety, and studies have shown that views of nature may provide positive psychological benefits.
According to the report, its findings suggest that “green vegetation has a protective effect,” and the association between greenness and lower mortality presents landscape architects, policy-makers, and urban planners with an “actionable tool” to increase green spaces and “grow healthier places.” While Kermit the Frog makes peace with being the color of leaves (“It’s beautiful,” he finally admits, “and it’s what I want to be”), Evanstonians can enjoy all the spring greenness in this Tree City and the possibility that it may be adding years to our lives.