Living in greener neighborhoods in middle age can slow cognitive decline and memory potential, a study has found. The study showed that increased exposure to residential green spaces may help delay cognitive decline by an average of eight months per year.
This delay was more noticeable among people who carry the APOE-ɛ4 allele (version) associated with an increased risk of Alzheimer’s disease.
Dementia prevention
Research has shown that around 40% of dementia cases worldwide could be prevented or delayed by addressing modifiable risk factors associated with the condition, particularly during midlife.
The new study, led by a researcher from Boston University School of Public Health, provides a deeper look at how living near green spaces such as parks and trees during middle age may provide cognitive benefits later in life.
The study, published in the journal Environmental Health Perspectives, found that living in areas with more green space during middle age may slow a person’s annual rate of cognitive decline by about eight months.
This association was also observed among people who carry the E4 allele of the apolipoprotein E gene, a type of the apolipoprotein E gene that is a major risk factor for Alzheimer’s disease.
The rate of cognitive decline was three times slower in people carrying the gene who were exposed to more green space than in people without the gene, an important research development given that there are no known ways yet to reduce the risk of dementia in carriers of the gene.
Exposure to green space has previously been linked to better cognitive function, but this new study includes a larger cohort and longer observational period than previous analyses. It is also the first to explore how different environmental features influence the relationship between green space and cognition among carriers of the APOE E4 allele.
Given that Alzheimer’s disease and related dementias may develop as much as 20 years before the characteristic symptoms appear, it is essential to identify the groups most at risk for these conditions and what preventive measures can be implemented early in life to prevent or slow cognitive decline.
“Our findings are important because they highlight the cognitive benefits of increased exposure to green space at the population level, especially among vulnerable subpopulations such as carriers of the E4 allele of the apolipoprotein E gene,” said study lead author Dr. Maria Pescador Jimenez, assistant professor of epidemiology at Boston University School of Public Health.
the study
To examine the relationship between residential green space, cognitive function and cognitive decline, Dr. Jimenez and colleagues from Rush Medical School, the Rush Alzheimer’s Disease Center and the Harvard T.H. Chan School of Public Health used data from the Nurses’ Health Study, a survey that began in 1976 and is one of the largest investigations of risk factors for chronic disease among women in the United States.
The team focused on 16,962 nurses aged 70 or older who were enrolled in a substudy that ran from 1995 to 2001 and continued through 2008. Participants were assessed on their cognitive function via telephone questionnaires, and the researchers used a satellite-based measure of green space levels around the participants’ residential areas. Green space exposure was assessed up to nine years before the first cognitive test, and the overall cognitive assessment included five cognitive tests administered up to four times over an average of six years.
After adjusting for age and socioeconomic factors, higher exposure to green space during midlife was associated with higher levels of cognitive function, as well as slower cognitive decline, based on global cognition scores, but not verbal memory.
little exposure to green spaces
The study also explored the role of mental health in the relationship between green space exposure in midlife and cognition. While previous research has suggested that limited exposure to green space in midlife can reduce cognitive function via depression, the new data extend this relationship by suggesting that green space may be linked to cognitive decline over time via mental health.
“The findings highlight the importance of prioritizing the preservation and creation of green spaces, especially in low-socioeconomic status neighborhoods, as a means of promoting cognitive health later in life,” says Dr. Pescador Jimenez.