Residential Green Space Linked to Better Cognitive Function

Dr Marcia Pescador Jimenez

Exposure to green space may boost cognitive function, new research suggests.

Results of a large prospective study show increasing exposure to residential green space was associated with significantly higher scores on cognitive function measures in middle-aged women compared with women who had less exposure.

This association may be explained by a reduction in depression, researchers note. Scores for overall cognition and psychomotor speed/attention among women with high green-space exposure were equivalent to those of women an average of 1.2 years younger, they add.

"Despite the fact that the women in our study were relatively younger than those in previous studies, we were still able to detect protective associations between green space and cognition," lead author Marcia Pescador Jimenez, PhD, assistant professor of epidemiology, Boston University School of Public Health, Massachusetts, told Medscape Medical News.

"This may signal the public health importance of green space and the important clinical implications at the population level," she said.

The findings were published online April 27 in JAMA Network Open.

Better Psychomotor Speed, Attention

Recent studies on the benefits of green space have shown a link between higher exposure and reduced risks for schizophrenia and ischemic stroke. Other studies have explored the link between green space and dementia and Alzheimer's disease.

Cognitive function in middle age is associated with subsequent dementia, so Jimenez said she and her colleagues wanted to analyze the effect of residential green space on cognitive function in middle-aged women.

The study included 13,594 women (median age, 61.2 years) who are participants in the ongoing Nurses' Health Study II, one of the largest studies to examine risk factors for chronic illness in women.

To calculate the amount of green space, researchers used the Normalized Difference Vegetation Index (NDVI), a satellite-based indicator of green vegetation around a residential address. The data were based on each participant's 2013 residence.

After adjusting for age at assessment, race, and childhood, adulthood, and neighborhood socioeconomic status, green space was associated with higher scores on the global CogState composite (mean difference per interquartile range in green space, 0.05; 95% CI, .02 - .07) and psychomotor speed and attention (mean difference in score, 0.05 standard units; 95% CI, .02 - .08) scales.

There was no association between green-space exposure and learning and working memory. Investigators also found no differences based on urbanicity, suggesting the benefits were similar for urban versus rural settings.

Specific to Cognitive Domains

"We were surprised to see that while our study found that higher levels of residential green space were associated with higher scores on processing speed and attention and on overall cognition, we also found that higher levels of residential green space were not associated with learning/working memory battery scores," Jimenez said.

"This is actually in-line with previous research suggesting differing associations between green space and cognition based on the cognitive domain examined," she added.

About 98% of participants were White, limiting the generalizability of the findings, the researchers note. There was also no information on proximity to or size of green space, or how much time individuals spent in the green space and what kinds of activities they engaged in.

Jimenez said projects examining the amount of time of green-space exposure are underway.

In addition, the researchers found lower rates of depression might contribute to the cognitive benefits associated with green-space exposure, explaining 3.95% (95% CI, .35% - 7.55%) of the association between green space and psychomotor speed/attention and 6.3% (95% CI, .77%-11.81%) of the association between green space and overall cognition.

Reduced air pollution and increased physical activity, which are other factors often thought to contribute to the cognitive benefits of green space, were not significant in this study.

"Interesting and Novel"

Commenting on the findings for Medscape Medical News, Payam Dadvand, MD, PhD, associate research professor, Barcelona Institute for Global Health, Spain, called the finding that depression may mediate green-space benefits "quite interesting and novel."

"The results of this study, given its large sample size and its geographical coverage, adds to an emerging body of evidence on the beneficial association of exposure to green space on aging, and in particular, cognitive aging in older adults," said Dadvand, who was not involved with the research.

The study was funded by the National Institutes of Health. Jimenez and Dadvand have reported no relevant financial relationships.

JAMA Netw Open. Published online April 27, 2022. Full article

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