Co-exposure to high PM2.5 and extreme heat exacerbates cognitive decline in middle-aged and elderly Chinese people

Cognitive impairment is an increasingly public health concern. However, limited evidence exists regarding the combined effects of fine particulate matter (PM2.5) and extreme heat exposure on cognitive function. Here, data from 3042 adults aged ≥45 years without baseline cognitive impairment across four waves (2011–2018) of the China Health and Retirement Longitudinal Study were collected, and Cox proportional hazards models with time-dependent covariates (counting process format) were used to estimate hazard ratios (HRs) for combined exposure of heat and PM2.5. Over the follow-up period, 763 participants of 3042 were diagnosed with cognitive impairment. Per 10 μg/m³ increase in PM2.5 (HR = 1.342, 95% confidence intervals (CI): 1.288–1.399) and higher cumulative exposure to extreme heat (HR = 1.032, 95% CI: 1.001–1.063) were independently associated with increased risk of cognitive impairment. Furthermore, participants with joint exposure to high PM2.5 and high heat had a 76% greater risk of cognitive impairment (HR = 1.959, 95% CI: 1.343–2.857), compared to those with low PM2.5 and high heat (HR = 1.111, 95% CI: 0.795–1.553). Subgroup analyses further revealed heterogeneity in the associations, with stronger risks observed among participants aged <65 years, men, and residents in the central region. These findings highlight the urgent need for integrated environmental and public health strategies to mitigate the cognitive impacts of air pollution and climate-related heat stress.