Growing evidence supports greater health benefits for people who live in ‘green’ neighborhoods – those with more tree canopy and street level vegetation specifically on the block where they live. A new study from researchers at the University of Miami Miller School of Medicine and the School of Architecture adds to this emerging recognition– finding a 28 percent lower risk for depression and 18 percent decreased risk for Alzheimer’s disease compared with residents of blocks low in greenness.
Interestingly, the association was even more pronounced in low-income areas. An increase from one standard deviation below to one standard deviation above the mean greenness level was associated with 37 percent lower odds of depression. In contrast, the risk decreased by 27 percent in medium-income neighborhoods and by 21 percent in high-income neighborhoods. The difference between low- and high-income neighborhoods was statistically significant for depression and trended toward significance for Alzheimer’s disease risk.
The findings were published online March 1 in the International Journal of Environmental Research & Public Health.
“One of the thoughts is in a lower-income neighborhood, you may have fewer resources to escape the impacts of your immediate neighborhood or block-level environment,” said lead study author Scott Brown, Ph.D., research assistant professor of public health sciences and architecture, and project director of the UM Built Environment, Behavior, and Health Research Team.
“People might be less likely on average to own a car compared to people in higher income neighborhoods. And they may be less likely to have a gym membership or go to a park in a different part of the city to maintain their levels of physical activity and social interaction.”
Even though some initial research suggested improvements in cognitive function associated with more neighborhood vegetation, “to our knowledge no one has looked at block-level greenness in relation to either of these two mental health outcomes,” Brown said.
Investigators focused on depression and Alzheimer’s disease because of their critical public health importance. “The World Health Organization considers depression one of the chronic conditions most likely to lead to disability in the world," Brown said. "Also, Alzheimer’s disease is currently in the No. 6 position for leading causes of death in the United States.”
Brown, along with José Szapocznik, Ph.D., professor of public health sciences, architecture, psychology, and educational and psychological studies; Joanna Lombard, M.Arch., professor of architecture and public health sciences; and their colleagues studied a population-based sample of 249,405 U.S. Medicare beneficiaries aged 65 years and older living in Miami-Dade County in the same location in 2010 and 2011. Medicare provides zip-plus-4 residential location data for recipients, which allowed researchers to pair mental health outcomes with block-level census data and to determine greenness based on the Normalized Difference Vegetation Index using satellite imagery.
The findings of the study could help physicians counsel at-risk patients with more specific recommendations based on where they live. “Oftentimes in the doctor-patient encounter there is a recommendation to exercise more in addition to the other recommendations,” Brown said. “But it may be important to know about the environment where the person lives.” Miami-Dade Parks offers programs at low cost or no cost for low-income populations, for example. “So there may be ways the physician can help the patient discover where it is they can engage in physical activity.”
Maria Nardi, director of Miami-Dade County Parks, Recreation and Open Spaces, participated as a co-author interpreting findings of the current research.
The investigators adjusted for age, gender, race/ethnicity and neighborhood income levels in their overall findings linking block-level greenness to better mental health outcomes. The current findings also align with previous work from Brown’s team showing greater improvements in obesity-related conditions such as diabetes, hypertension and hyperlipidemia among Medicare recipients living on blocks with greater greenness.
The new findings also support studies from other researchers, including a similar study in Wisconsin.
More research is needed to determine the extent to which these findings in South Florida can be generalized to areas with more seasonal variation in foliage, Brown said. More work also is needed to replicate the findings, particularly the decreased risk for Alzheimer’s disease, “which is a novel, first-ever finding.” Grants from the U.S. Department of Housing and Urban Development, the Health Foundation of South Florida and the Parks Foundation of Miami-Dade County supported the study.
In addition, building on their current research, the UM researchers recently received funding from the Robert Wood Johnson Foundation’s Evidence for Action (E4A) program to assess the impacts of greening interventions, such as tree planting, on cardiovascular health in Miami-Dade County neighborhoods over the past seven years. This work could provide further evidence to support expanding Miami-Dade’s tree canopy, an initiative already under way through Miami-Dade’s Million Trees Miami program.