Living in Areas With More Greenery May Boost Cognitive Function

Summary: Living near green spaces improves processing speed, cognitive function, and attention in addition to improving mental health, researchers report.

Source: Boston University

Cognitive function at middle age is a strong predictor of whether a person may develop dementia later in life.

Now, a new study led by a Boston University School of Public Health (BUSPH) researcher has found that increasing greenspace in residential areas could help improve cognition function in middle-aged women and that this association might be explained by a reduction in depression, which is also a risk factor for dementia.

Published in the journal JAMA Network Open, the study found that exposure to greenspace around one’s home and surrounding neighborhood could improve processing speed and attention, as well as boost overall cognitive function.

The results also showed that lowered depression may help explain the association between greenspace and cognition, bolstering previous research that has linked exposure to parks, community gardens, and other greenery with improved mental health.

“Some of the primary ways that nature may improve health is by helping people recover from psychological stress and by encouraging people to be outside socializing with friends, both of which boost mental health,” says Dr. Marcia Pescador Jimenez, study lead and corresponding author, and assistant professor of epidemiology at BUSPH.

“This study is among the few to provide evidence that greenspace may benefit cognitive function in older ages. Our findings suggest that greenspace should be investigated as a potential population-level approach to improve cognitive function.”

For the study, Pescador Jimenez and colleagues from BUSPH, Harvard T.H. Chan School of Public Health, Brigham and Women Hospital, Harvard Medical School, and Rush Medical College estimated residential greenspace with a satellite image-based metric called the Normalized Difference Vegetation Index (NDVI).

They measured psychomotor speed, attention, learning, and working memory among 13,594 women aged 61 on average and primarily White, from 2014 to 2016.

The women were participants in the Nurses’ Health Study II, the second of three studies that are among the largest investigations into the risk factors for chronic diseases among US women.

Adjusting for age, race, and individual and neighborhood socioeconomic status, the researchers found that greenspace exposure was associated with psychomotor speed and attention, but not learning or working memory.

In addition to depression, the researchers also examined the potential roles of air pollution and physical activity in explaining the association between greenspace and cognitive function, and they were surprised to only find evidence of depression as a mediating factor.

“We theorize that depression might be an important mechanism through which green space may slow down cognitive decline, particularly among women, but our research is ongoing to better understand these mechanisms,” Pescador Jimenez says.

“Based on these results, clinicians and public health authorities should consider green space exposure as a potential factor to reduce depression, and thus, boost cognition. Policymakers and urban planners should focus on adding more green space in everyday life to improve cognitive function.”

While the study shows evidence of this association, the greenspace metric that the researchers used to measure greenspace exposure does not differentiate between specific types of vegetation. In a new project, Pescador Jimenez will apply deep learning algorithms to Google Street View images to better understand which specific elements of greenery, such as trees or grass, could be the driving factors for health.

The researchers also hope that their study is replicated among other racial/ethnic populations and assesses associations with cognitive decline over longer periods of time.

“The distribution of green spaces in cities is not uniform,” says Pescador Jimenez. “Increasing everyday access to vegetation across vulnerable groups in urban cities is a crucial next step to achieve health equity.”

Abstract

Residential green space and cognitive function in a large cohort of middle-aged women

Importance

Green space can decelerate cognitive decline by supporting physical activity, psychological restoration, or reducing exposure to air pollution. However, existing studies on the association of green space with cognitive decline are limited.

Objective

To examine whether residential green space was associated with cognitive function in middle-aged women.

Design, Setting, and Participants

Starting in 1989, the Nurses’ Health Study II enrolled 116 429 female nurses aged 25 to 42 years residing in the US. In 2014 to 2016, 40 082 women were invited to complete an online cognitive battery. This cohort study analyzed women who had data on both green space exposure and cognitive measures. Data analysis was conducted from June to October 2021.

Exposures

Residential exposure to green space was assessed using the Normalized Difference Vegetation Index, a satellite-derived indicator of the quantity of ground vegetation. Landsat satellite data at 270-m and 1230-m buffers around each participants’ residential addresses in 2013 were used.

Main Outcomes and Measures

In 2014 to 2016, cognitive function was measured using a self-administered online battery, the Cogstate Brief Battery, consisting of 4 tasks measuring psychomotor speed, attention, learning, and working memory; 3 composite scores, averaging together all tasks, psychomotor speed/attention, and learning/working memory, were created. In addition, the study evaluated potential mediators, including air pollution, depression, and physical activity.

Results

The analytical sample included 13 594 women, of whom 13 293 (98%) were White. Mean (SD) age was 61.2 (4.6) years. In models adjusted for age at assessment, race, childhood, adulthood, and neighborhood socioeconomic status, green space was associated with higher scores on the global Cogstate composite (mean difference per IQR in green space, 0.05; 95% CI, 0.02 to 0.07), and psychomotor speed/attention (mean difference in score, 0.05 standard units; 95% CI, 0.02 to 0.08). This difference in scores is similar to the difference observed in women 1 year apart in age in the data. By contrast, there was no association between green space and learning/working memory (mean difference, 0.0300; 95% CI, −0.0003 to 0.0500).

Conclusions and Relevance

These findings suggest that increasing residential green space may be associated with modest benefits in cognition in middle-aged women.