Health in All Policies: The Impact of the Healthy City Pilot Policy on Cognitive Health and Cognitive Health Inequality Among Older Adults in China—Evidence from Difference-in-Differences and Double Machine Learning

Background Cognitive decline among older adults is an important public health concern in the context of population aging. Although cognitive health in later life is shaped by broader social and environmental conditions, limited evidence exists on whether health-oriented urban governance can improve cognitive health and reduce cognitive health inequality. This study evaluated the impact of China’s Healthy City pilot policy on cognitive health and cognitive health inequality among older adults. Methods Data were drawn from the 2013, 2015, 2018, and 2020 waves of the China Health and Retirement Longitudinal Study, combined with city-level socioeconomic data and Healthy City pilot information. The final sample included 28,193 observations from adults aged 60 years and above. Cognitive health was measured using CHARLS cognitive assessment items, and cognitive health inequality was measured using the cognitive health relative deprivation index. Difference-in-differences models with city and year fixed effects were used to estimate policy effects. Double machine learning with Lasso and five-fold cross-fitting was also used to account for high-dimensional covariates and nonlinear relationships. Mechanism and heterogeneity analyses were conducted. Results The Healthy City pilot policy significantly improved cognitive health and reduced cognitive health inequality. In the fully adjusted difference-in-differences model, the policy increased cognitive health by 0.677 points and reduced the cognitive health relative deprivation index by 0.018. Double machine learning produced similar estimates, with effects of 0.6678 on cognitive health and − 0.0182 on the cognitive health relative deprivation index. Robustness checks supported the stability of the findings. Mechanism analyses suggested that the policy reduced inequality through improved clean energy use, increased social participation and physical activity, reduced smoking, and enhanced digital inclusion. The effect was stronger among older individuals, men, older adults without children, and those living in western China, but weaker among older adults with ADL impairment. Conclusions The Healthy City pilot policy improved cognitive health and reduced cognitive health inequality among older adults in China. Health-oriented urban governance may promote cognitive health equity through living environments, health behaviors, social participation, and digital inclusion. Future healthy city and healthy aging strategies should emphasize cognitive health promotion and targeted support for vulnerable older adults.