Ambient air pollution exposure and cognitive aging; mediators and possible pathways: a systematic review on the epidemiological studies.
This systematic review investigates the mediating factors in the relationship between ambient air pollution exposure and cognitive aging. We identified 16 studies examining 72 unique exposure-mediator-outcome associations for six pollutants (PM2.5, PM10, NO2, NOX, black carbon, and PM1 components). The most studied pollutant was PM2.5 (65% of analyses). Cognitive outcomes included memory, cognitive processing speed, and clinically diagnosed conditions such as dementia incidence. Potential mediators spanned mental health outcomes (depression, anxiety, stress), lung function (FEV1, FVC, PEF), vascular diseases (stroke, hypertension), inflammation (CRP), metabolic factors (type 2 diabetes), sleep, and neuroanatomical changes. The quality of mediation analysis reporting was generally good, but most studies had some risk of bias, particularly in outcome assessment and confounding adjustment. Cardio and Cerebro-vascular diseases emerged as a potential key mediator. Mental health outcomes, sleep, and lung function also showed mediating potential, but further research is needed to confirm these findings. This review highlights the need for rigorous causal mediation analyses and standardized reporting to better understand the complex pathways linking air pollution to cognitive aging, in order to identify targeted preventive measures to reduce the negative impact of ambient air pollution on cognitive health.