Living Near Greenspace Slows Cognitive Decline

Researchers examined the relationship between midlife residential greenness and cognitive decline later in life, taking into account the impacts of socioeconomic position, rural/urban residency, and apolipoprotein E (APOE)-ɻ4 status. Their findings were published in the Environmental Health Perspectives.

Background

Cognitive decline is a major feature of Alzheimer’s disease and related dementia (ADRD), a collection of brain illnesses that cause memory loss and cognitive decline. ADRD can start decades before symptoms manifest.

To prevent dementia, research into new risk factors for cognitive decline is essential. According to studies, residential greenness may enhance cognitive function by lowering stress, restoring focus, reducing air pollution, promoting physical exercise, and fostering social connections.

But the majority of research is cross-sectional. Dementia risk is significantly influenced by midlife risk factors such as vascular problems, psychological stress, and physical inactivity. The allele APOE-ɛ4 is a noteworthy genetic risk factor.

More investigation is required to validate the long-term correlation between midlife residential greenness and cognitive decline, as well as to determine the best interventions for various populations, such as socioeconomically disadvantaged groups and APOE-ɛ4 carriers.

About the study
When the Nurses’ Health Study (NHS) was first launched in 1976, it included 121,700 female nurses in 11 US states who were between the ages of 30-55. Today, the study covers the whole nation. With almost 90% follow-up, participants completed biannual health surveys.

Women 70 years of age or older who had never had a stroke participated in an institutional review board-approved study, which examined cognitive function between 1995 and 2001.

92% of 22,715 eligible women took part in the study at first, and more than 90% did so for the three follow-ups that were conducted until 2008. 16,962 women who had at least one cognitive testing were included in the analysis.

Between 1986 and 1994, midlife greenness exposure was assessed within 270- and 1,230-meter buffers surrounding residential properties using the Normalized Difference Vegetation Index (NDVI).

Six tests were used in telephone interviews to evaluate cognitive function, and verbal memory and general cognition composite z-scores were used. Covariates included body mass index (BMI), mental health, physical activity, air pollution, mental health, and social engagement in addition to socioeconomic level (SES).

After hierarchically adjusting for age, SES, mental health, and antidepressant usage, midlife greenness and cognitive decline were evaluated using linear mixed models.

The interaction terms examined how SES, urbanization, and APOE-ɛ4 status affected effect modification. Sensitivity studies addressed modifications and removed recent movers and subjects with low baseline cognitive function.

The APOE-ɛ4 status was ascertained using buccal or blood samples. The mediation analysis examined the impacts of greenness on cognition through physical activity, social interaction, air pollution, and mental health using SAS and R software.

In conclusion
Based on global cognition scores, a larger midlife exposure to greenness was linked to better baseline cognitive performance and a slower pace of cognitive decline in this large prospective research of women.

Stronger correlations were discovered in the study among APOE-̻4 carriers and in low-SES and high-density communities. A mediation analysis revealed that a portion of the relationship between midlife greenness and cognitive results could be explained by mental health.

According to these results, midlife greenness may be a controllable factor in lowering the incidence of dementia, especially for people who are more genetically predisposed to the condition and live in underprivileged areas.

For more information: Midlife Residential Greenness and Late-Life Cognitive Decline among Nurses’ Health Study Participants, EHP, https://doi.org/10.1289/EHP13588