Frailty, a geriatric syndrome characterized by increased vulnerability due to age-related decline and chronic diseases, poses a significant public health challenge, especially in rapidly aging populations like China. This syndrome is associated with increased risks of hospitalization, falls, depression, and mortality. While studies have shown a protective association between overall greenness (measured by Normalized Difference Vegetation Index, NDVI) and frailty, the impact of specific greenspace structures remains less understood. This research aims to fill this gap by investigating the relationship between various structural characteristics of greenspaces and frailty among a large cohort of older Chinese adults. The study's importance lies in its potential to provide evidence-based insights for urban planning and environmental design, ultimately contributing to improved health outcomes and healthy aging in older populations. Understanding the impact of greenspace structures, beyond simple vegetation density, could lead to more effective strategies for promoting healthy aging and mitigating frailty in urban environments. The design and layout of green spaces can impact their effectiveness. This study explores the relationship between specific structural characteristics of greenspaces and frailty, offering valuable information for urban planning and promoting healthy aging.

Existing literature has established a link between greenness and various health outcomes, including frailty. Studies using NDVI, a measure of vegetation density, have demonstrated the positive effects of residential greenness on reducing frailty-related problems, possibly through mechanisms such as increased physical activity, improved cognitive function, enhanced social cohesion, and reduced stress. However, these studies primarily focused on overall greenness rather than the specific structural characteristics of greenspaces. This research aims to address this gap by exploring the association between three key structural aspects of greenspaces—area-edge, shape, and proximity—and frailty. Previous research suggests that different structural characteristics of green spaces may impact health outcomes through various pathways. For instance, larger and more connected green spaces might promote physical activity, while complex shapes could enhance psychological well-being and stress reduction. Thus, this study advances previous research by focusing on the nuanced relationship between the structural characteristics of green spaces and the risk of frailty.

This study utilized data from the 2008-2014 China Longitudinal Healthy Longevity Survey (CLHLS), a nationally representative survey of older adults in China. The study sample included 8776 individuals after excluding those with missing data on demographics, frailty index, and NDVI. Greenspace structure was quantified at the county level using satellite imagery and landscape indices derived from the Advanced Land Observing Satellite (ALOS) data. Three indices were employed: the largest patch index (LPI), representing area and edge; the mean shape index, reflecting shape complexity; and the patch cohesion index, indicating proximity and connectivity. Frailty was assessed using the frailty index (FI), a composite score based on 39 self-reported items related to physical, cognitive, and psychological health. Both cross-sectional and longitudinal analyses were performed. Cross-sectional analyses used linear and logistic regression to examine the associations between greenspace indices and FI at baseline, controlling for potential confounders such as age, sex, socioeconomic status, and lifestyle factors. Longitudinal analyses, employing generalized estimating equations (GEE), investigated the changes in FI over time in relation to greenspace indices. Sensitivity analysis was conducted using alternative landscape indices to evaluate the robustness of the findings. Subgroup analyses were performed to assess potential effect modification based on sex, age, literacy, residential location, marital status, and changes in FI.

Cross-sectional analyses revealed significant negative associations between higher values of LPI, shape index, and cohesion index and frailty. Participants in the highest quartile of each index had substantially lower odds of being frail compared to those in the lowest quartile. Specifically, individuals in the highest quartile of LPI, shape, and cohesion had 32%, 35%, and 37% lower odds of frailty, respectively. These associations were particularly strong among females, centenarians, illiterate individuals, city residents, unmarried individuals, and those with a higher baseline FI. However, these significant associations were not observed in the longitudinal GEE analysis, which did not show a significant association between greenspace structure and changes in frailty over time. Sensitivity analyses using alternative landscape indices yielded similar results, reinforcing the robustness of the findings. The analysis also included NDVI, which showed an association with reduced frailty in cross-sectional analysis but not longitudinally.

The cross-sectional findings of this study suggest a protective association between residential greenspace structures and frailty among older Chinese adults. Larger, more complex, and more connected greenspaces may contribute to lower frailty risk, potentially through several mechanisms. These include increased opportunities for physical activity, improved psychological well-being, reduced exposure to air pollution, and enhanced social interaction. The stronger associations observed in certain subgroups (females, centenarians, etc.) might reflect differential vulnerability to frailty or differential access to and utilization of greenspaces. The lack of significant associations in longitudinal analysis could be attributed to several factors, including attrition (high death rate in the study group), limitations of the study design, or unmeasured confounding. The findings highlight the potential benefits of strategically designing and planning greenspaces, especially in urban areas, to promote healthy aging and mitigate frailty.

This study provides valuable evidence supporting the association between residential greenspace structures and lower frailty risk among older Chinese adults, particularly in cross-sectional analyses. While the longitudinal association remains inconclusive, the findings underscore the importance of incorporating greenspace structural characteristics into urban planning initiatives aimed at promoting healthy aging. Future research should investigate the underlying mechanisms linking greenspace structures and frailty, address the limitations of longitudinal analyses, and explore the interaction between various greenspace features and other factors influencing frailty.

This study has several limitations. The significant attrition in the longitudinal analysis due to deaths and loss to follow-up might have impacted the findings. The use of county-level data on greenspace structure, rather than individual-level data, could have introduced ecological fallacy. The study did not consider the specific types of vegetation or the amount of time individuals spend in greenspaces. The cross-sectional design prevents establishing causality, and the possibility of confounding factors remains.