Residential green spaces and neurodegenerative diseases in middle-aged and older adults: a systematic review and dose-response meta-analysis

BACKGROUND: The potential protective role of residential green space against neurodegenerative diseases (NDs) is a topic of growing interest, yet evidence remains inconsistent. This systematic review and meta-analysis aimed to synthesize the current evidence on this association in middle-aged and older adults. METHODS: We searched PubMed, Embase, Web of Science, and the Cochrane Library through March 15, 2025, for observational studies that evaluated the association between objectively measured residential green space and the incidence of NDs in middle-aged and older adults. Risk of bias was assessed using the Newcastle-Ottawa Scale (NOS) and the ROBINS-E tool. Random-effects models were used to pool multivariate-adjusted risk estimates comparing the highest versus lowest exposure categories. Subgroup analyses were conducted by disease type (Alzheimer's disease, Parkinson's disease, and cognitive impairment) and other study characteristics. In addition, a dose-response meta-analysis was performed to explore the potential nonlinear relationship between residential green space exposure and NDs risk. The certainty of evidence was assessed using the GRADE framework. RESULTS: A total of twelve studies involving over 1.7 million participants were included. Higher residential green space exposure was associated with a lower risk of NDs (pooled HR = 0.85, 95% CI: 0.79-0.91). Subgroup analyses suggested that the inverse association was generally consistent across different disease types, although the magnitude of association varied. The dose-response analysis indicated a nonlinear association, with risk reductions observed at increasing levels of green space exposure, followed by a plateau at higher exposure levels. However, this association was accompanied by extremely high and unexplained statistical heterogeneity across studies (I² > 90%). CONCLUSIONS: Our findings suggest a potential protective association between residential green space and NDs. This conclusion must be interpreted with extreme caution, as the overall certainty of the evidence was rated "Very Low" due to profound inconsistency and a serious risk of bias in the primary studies. Methodologically rigorous longitudinal research with improved exposure assessment is urgently needed to provide more definitive evidence. TRIAL REGISTRATION: The study protocol received prospective registration in the International Prospective Register of Systematic Reviews (PROSPERO; registration number: CRD420251020592).