Introduction Proximity to vegetated green space has been linked to better physical and mental health. However, the relationship between residential greenness and cognitive function and its decline among older adults is not clear in large cohort studies.
Methods Our study used the 2000, 2002, 2005, 2008 and 2011 wave of the Chinese Longitudinal Healthy Longevity Survey. We calculated the Normalised Difference Vegetation Index (NDVI) using a 500 m radius around participants’ residential addresses. Mini-Mental State Examination (MMSE) was applied to measure cognitive function. Our study included the cross-sectional analysis using the linear regression, and logistical regression, and also the longitudinal analysis using the linear mixed effects regression, and mixed effects logistic regression. Our study also conducted a sensitivity analysis using the survey-weighted regression. Additionally, our study participants were categorised into those living in areas of positive and negative changes in NDVI in relation to MMSE. All regression models were adjusted for a range of covariates.
Results Among 38 327 participants at baseline, the mean MMSE score was 21. Annual average NDVI ranged from −0.11 to 0.76. In the cross-sectional analysis, each 0.1-unit increase in NDVI was associated with a 0.23-point increase in MMSE score (95% CI 0.16 to 0.29) in the linear regression, and an OR of 0.94 (95% CI 0.92 to 0.96) of having cognition impairment in the logistic regression. In the second analysis, looking at changes in NDVI and MMSE score, compared with the participants living in areas with an increase in NDVI, those living in areas with a decrease in greenness had an OR of 1.25 (95% CI 1.18 to 1.34) of a decrease in MMSE, and an OR of 0.90 (95% CI 0.84 to 0.96) of an increase in MMSE. In the longitudinal analysis, we found a significantly weak association (coefficient 0.069, 95% CI 0.0048 to 0.13) in the linear mixed effects regression, but not in the mixed effects logistic regression.
Conclusion We found evidence of an association between higher residential greenness and better cognitive function among older adults. Our finding provides insight into neurodegeneration and has implications for preventing dementia and Alzheimer’s disease in China.
- residential greenness
- Normalised Difference Vegetation Index
- cognitive function
- Mini-Mental State Examination (MMSE)
- environmental epidemiology
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Contributors AZ and JSJ conceived and designed the study design, conducted statistical analysis and drafted the manuscript. AZ, CB, C-DW and JSJ developed the exposure assessment for residential greenness. CW, LY, XS and YZ provided inputs on CLHLS data structure. All the authors contributed to the interpretation of findings, provided revisions to the manuscript and approved the final manuscript.
Funding This study was supported by the Bill & Melinda Gates Foundation (Grant number: OOP1148464). The data analyzed in this paper were provided by the Chinese Longitudinal Healthy Longevity Study (CLHLS) which has been jointly supported by National Natural Sciences Foundation of China (71490732) and the National Key R&D Program of China (2018YFC2000400).
Disclaimer The funders of the study had no role in study design; collection, analysis and interpretation of data; or manuscript drafting.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval The study protocol was approved by the Institutional Review Board, Duke University (Pro00062871), and the Biomedical Ethics Committee, Peking University (IRB00001052-13074). Paper-based informed consent was signed and collected from all participants.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available on reasonable request.
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