Association between long-term exposure to air pollutant mixture and the risk of Alzheimer’s disease among older people: a prospective cohort study in China

Alzheimer's disease (AD) has garnered significant attention in recent years. However, evidence of the association between air pollutant mixture and AD from prospective studies has not been systematically explored. We aimed to examine the associations of combined exposure to nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), and particulate matter (PM) with diameters of ≤ 2.5 μm (PM2.5) or ≤ 10 μm (PM10) with AD, and to further investigate the potential modifiable effects of lifestyle factors and air pollution. Our study was based on the Zhejiang Province Major Public Health Surveillance (ZJMPHS) Program. The concentrations of five air pollutants were estimated via the empirical Bayesian kriging (EBK) spatial interpolation method, and we applied a weighted joint air pollution score (JAPS) to evaluate their combined effects. AD was ascertained according to the Diagnostic and Statistical Manual of Mental Disorders and Statistics (DSM-IV) and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association-Alzheimer's Criteria (NINCDS-ADRDA). The Cox proportional hazards models were used to explore the associations between air pollution and AD. A total of 10,055 participants aged ≥ 60 years were included in the analysis. During a follow-up period of 34,764 person-years, 879 AD cases were identified. SO2, PM2.5, and PM10 were positively associated with AD, with HRs of 1.11 (95% CI, 1.09, 1.14), 1.03 (95% CI, 1.02, 1.05) and 1.03 (95% CI, 1.02, 1.04), respectively. High JAPS (based on the median) was related to higher risk of AD (HR = 2.16, 95% CI: 1.87, 2.51). The extremely high JAPS (based on the third percentile) significantly increased the risk of AD (HR = 2.31, 95% CI: 2.01, 2.65). Significant (or borderline) interactions between JAPS and exercise (p = 0.009) and living alone (p = 0.058) were found, which both amplify the incidence density of AD in extremely high JAPS. This study suggested that high concentration of air pollutant mixture could increase the risk of AD. Moreover, it is important to weigh the impact of exercise under extremely high air pollution and pay attention to those who live alone.