Association between urban green space coverage and incident Alzheimer’s disease among older adults in metropolitan South Korea: a population-based retrospective cohort study

Background Urban green space (UGS) may support cognitive health in later life, but longitudinal evidence from rapidly aging Asian cities remains limited. We examined the association between officially designated UGS coverage and incident Alzheimer's disease (AD) among older adults in metropolitan South Korea. Methods This population-based retrospective cohort study used the Korean National Health Insurance Service database linked to health screening data. We included 95,822 adults aged 65 years or older residing in seven metropolitan areas who underwent health screening in 2009–2010. UGS coverage in 2010 was defined as the proportion of officially designated parks and open green spaces within each residential district and categorized into quartiles. Participants were followed from January 1, 2011, until incident AD, death, or December 31, 2023. Cox proportional hazards models estimated adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs). Results During follow-up, 21,733 incident AD cases occurred, with incidence rates of 24.71, 21.04, 19.14, and 22.17 per 1,000 person-years across Q1–Q4. In the fully adjusted model, higher UGS coverage was associated with modestly lower AD risk (aHR 0.96 [95% CI, 0.92–0.999] for Q2, 0.90 [0.86–0.94] for Q3, and 0.94 [0.90–0.97] for Q4; P for trend < 0.001). Conclusions Higher UGS coverage was associated with a lower risk of incident AD among older adults in urban South Korea. These findings support further investigation of urban green infrastructure as a potentially modifiable environmental factor for cognitive health in aging populations.