Systematic review of nonlinear associations between the built environment and walking in older adults.

backgroundIn the context of global population aging, walking has become a key form of daily physical activity for older adults. Walking supports social participation and independence, and contributes significantly to both physical and mental health. However, there is still no broad consensus on which built environment factors influence older adults’ walking, or how these factors exert their effects.

methodsThis study systematically searched five databases: MEDLINE, Web of Science, PubMed, Scopus, and Embase. Inclusion and exclusion criteria were defined using the PICOS framework. The review followed PRISMA guidelines, and studies were summarized according to their characteristics, methodological features, and built environment variables. The 46 included studies were assessed for quality using the National Institutes of Health’s Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. Based on this evaluation, a quantitative analysis identified 11 built environment factors with strong consensus regarding their influence on walking activity among older adults.

resultsThis study systematically reviewed 46 empirical studies to examine the impacts and mechanisms of the built environment on walking activity among older adults. The results indicate that the availability of retail stores, perceived safety, and aesthetic appeal significantly promote walking. In contrast, factors such as population density, residential density, land-use mix, intersection density, green view ratio, sidewalk density, distance to parks, green spaces, and plazas, as well as transit stop density, exhibit nonlinear effects. The nonlinear relationships involving sidewalk density and the distance to parks, green spaces, and plazas remain contested. Specifically, the following thresholds warrant attention: the optimal range of population density remains inconclusive and requires further validation; land-use mix is most effective within 0.55–0.7; intersection density is optimal at 25–65/km2; a streetscape green view index of about 24% yields the greatest effect; residential density of 10,000–25,000 households/km2 provides the strongest support for walking; sidewalk density of approximately 6 km/km2 is particularly relevant; the acceptable maximum walking distance to parks, green spaces, or plazas is 1–1.3 km; and transit stop density is preferable at 6–7 stops/km2. In addition, sufficient neighborhood shops and convenience facilities are needed to strengthen motivation for walking. Safety and aesthetic appeal play a key role in promoting walking by enhancing environmental perception and psychological sense of safety.

conclusionsFuture research should adopt more longitudinal designs to overcome the limited causal inference of cross-sectional studies and to explore methods for controlling self-selection bias. In addition, future studies should strengthen the investigation of nonlinear relationships between the built environment and walking activity among older adults, with a focus on fine-grained analyses at the micro level. Integrating AI, big data, and machine learning for dynamic prediction and mechanism modeling will further help to uncover the complex interactions between the built environment and walking behavior. The findings of this study are consistent with the World Health Organization’s (WHO) core concept of “age-friendly cities” and provide actionable theoretical and practical guidance for human-centered, age-friendly urban design.