Research has shown that about 40% of dementia cases worldwide could be prevented or delayed by addressing certain risk factors, especially during midlife.
A new study led by a researcher from Boston University School of Public Health (BUSPH) reveals that living near greenery, such as parks and trees, during middle age can slow cognitive decline later in life.
Published in the journal Environmental Health Perspectives, the study found that people living in greener areas during midlife may experience a slower rate of cognitive decline, equivalent to an eight-month delay.
This effect was particularly strong among people living in low-income, densely populated neighborhoods.
The study also found that people with the APOE-ɛ4 gene, which increases the risk of Alzheimer’s disease, benefited significantly from exposure to greenery.
Those with this gene experienced a threefold slower rate of cognitive decline compared to those without the gene. This is important because there are currently no known ways for APOE-ɛ4 carriers to reduce their dementia risk.
Previous studies have linked exposure to greenery with better cognitive function, but this new study included a larger group of participants and a longer observation period. It is also the first study to explore how different environmental features, like parks and trees, affect cognitive function among APOE-ɛ4 carriers.
Considering that Alzheimer’s and related dementias can develop up to 20 years before symptoms appear, it is crucial to identify vulnerable populations and implement protective measures early to slow or prevent cognitive decline.
“Our results highlight the cognitive benefits of increasing green space exposure at a population level, especially for vulnerable groups like APOE-ɛ4 gene carriers,” says Dr. Marcia Pescador Jimenez, the study’s lead author and assistant professor of epidemiology at BUSPH.
To explore the link between living near greenery and cognitive function, Dr. Pescador Jimenez and her colleagues from Rush Medical College, Rush Alzheimer’s Disease Center, and Harvard T.H. Chan School of Public Health used data from the Nurses’ Health Study (NHS). This large study began in 1976 and focuses on the risk factors for chronic diseases among U.S. women.
The team focused on 16,962 nurses aged 70 or older who were part of an NHS substudy from 1995 to 2008. The participants’ cognitive function was assessed through phone surveys, and the researchers used satellite images to measure greenery levels around their homes. They looked at greenery exposure up to nine years before the first cognitive test and conducted five cognitive tests up to four times over an average of six years.
After adjusting for age and socioeconomic factors, the study found that higher exposure to greenery during midlife was linked to better cognitive function and slower cognitive decline, especially in global cognition scores but not in verbal memory.
This association was stronger for participants in low-income, densely populated neighborhoods, suggesting that increasing greenery in disadvantaged areas could help reduce health inequalities.
“Our findings for participants in lower socioeconomic status neighborhoods support the theory of equigenic environments, which suggests that greenery might help reduce health inequalities,” Dr. Pescador Jimenez says.
The study also examined the role of mental health in the relationship between midlife greenery exposure and cognitive function. While previous research suggested that lack of greenery in middle age can decrease cognitive function through depression, this study extends the connection by suggesting that greenery might help slow cognitive decline over time through its positive effects on mental health.
“These findings emphasize the importance of preserving and creating green spaces, especially in low-income neighborhoods, to promote cognitive health later in life,” says Dr. Pescador Jimenez.
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