Reference
Jimenez MP, Elliott EG, DeVille NV, et al. Residential green space and cognitive function in a large cohort of middle-aged women. JAMA Netw Open. 2022;5(4):e229306. doi:10.1001/jamanetworkopen.2022.9306
Study Objective
To investigate whether exposure to residential green space is associated with cognitive function in middle-aged women
Key Takeaway
Residency in an area with increased green space was associated with better cognitive function in middle-aged female nurses and should be further investigated as a potential population-level approach to improving cognitive function.
Design
Prospective, observational cohort study
Participants
The cohort used in this study is part of the ongoing Nurses’ Health Study II (NHS II).1 Beginning in 1989, the NHS II enrolled female nurses aged 25 to 42 years at the time of enrollment (N=116,429).
Between 2014 to 2016, investigators invited 40,082 NHS II participants to participate in the current study, of which 14,151 completed the self-administered cognitive exam (Cogstate Brief Battery).
The total sample at the time of analysis (2021) was 13,594 (mean age 61.2 years).
All study participants lived in the United States, and researchers adjusted for socioeconomic status; 98% of participants were white.
Study Parameters Assessed
The Cogstate Brief Battery is a self-administered test that includes 4 tasks designed to be a sensitive indicator of early cognitive deficits. Using this validated test, investigators computed 3 composite scores:
- A psychomotor speed/attention score
- A learning/working memory score
- An overall cognition score
Additionally, data from the Normalized Difference Vegetation Index, which assesses green space via satellite imaging, was used to determine each participant’s residential green space.
Primary Outcome
The study looked at participants’ scores on the Cogstate Brief Battery, which is a computer-based cognitive assessment tool that can be used to measure cognition.
Key Findings
This study found that increasing green space is associated with higher scores for overall cognition and psychomotor speed/attention. However, there was no difference in learning or working memory.
An increase by 1 interquartile range (IQR) in green space exposure within a 270-m (886-feet) buffer zone was associated with higher scores on psychomotor speed/attention composite (β, 0.04; 95% CI, 0.02 to 0.07) and overall cognition (β, 0.04; 95% CI, 0.01 to 0.06). Adjustment for individual childhood and adulthood socioeconomic status did not significantly change the results. These associations were still positive when the buffer zone was changed to 1,230 m (3/4 of a mile) (β, 0.04; 95% CI, 0.02 to 0.07) and (β, 0.04; 95% CI, 0.02 to 0.06).
The association between green-space exposure and learning/working memory composite was positive but not statistically significant using the 230-m or 1,230-m buffer zones (β, 0.03; 95% CI, –0.00 to 0.05) and (β, 0.02; 95% CI, –0.01 to 0.04).
Transparency
The study was funded by National Institutes of Health grants to Dr Jimenez, Dr Weuve, and Dr James. Dr Weuve reported receiving personal fees from the Alzheimer’s Association and personal fees from the Health Effects Institute outside of this work.
Practice Implications & Limitations
Human exposure to nature as green space, and the ramifications thereof, has become increasingly interesting to researchers. Perhaps the consideration that nature, in and of itself, is foundational to the human experience and, therefore, would be expected to impact the human body in numerous ways, is rightly compelling in an age when 55% of the world’s population lives in urban areas and with 68% of the world population projected to live in urban areas by 2050.2 Researchers are investigating the importance of exposure to green space and the connection to neurological health as access and exposure to nature and wild areas potentially become less accessible to a growing global population increasingly residing in urban areas.
The last few decades have yielded a growing body of data supporting numerous positive neurological associations with exposure to green space, including the impact on cognition in children,3,4 recovery time from surgical events,5 dementia,6 mental health,7 and more. When working with patients experiencing issues with cognition and mental health, etc., practitioners may rightly consider asking patients about access to and time spent in nature and, depending on their answer, encouraging them to increase their time in nature.
It should be noted that the Normalized Difference Vegetation Index (NDVI), though valuable as a research tool to inform green space within study parameters, has its own challenges. Researchers recently reported that it “may do a poor job of fully characterizing the human experience of being exposed to trees and plants, because scenes with the same normalized difference vegetation index value can appear different to the human eye."8 Despite being a powerful tool, the NDVI cannot discern the full reality of study participants’ experience with and exposure to nature as green space.9 For example, urban dwellers may intentionally seek green space opportunities, and this would confound the results.
Follow-up studies should investigate the effect of actual behaviors and time spent in natural settings. Furthermore, this study should help inform urban planners who are in a position to influence the amount of green space in cities and neighborhoods as the population in these areas increases.
Lastly, this study is limited by its narrow patient population, as it essentially assesses only middle-aged, white, female nurses. This study may also be of limited relevance to individual practitioners as it was not designed to determine if habitually exposing oneself to green space improves cognition. It demonstrates only the effect of residing closer to green space, something that individual practitioners have little influence over.
