Ambient air pollution exposure and cognitive aging, mediators and possible pathways: A systematic review on the epidemiological studies.

In 30 seconds

This systematic review examined epidemiological evidence on factors that may mediate associations between ambient air pollution and cognitive aging. It included 16 studies covering 72 exposure–mediator–outcome associations across six pollutants; PM2.5 accounted for 65% of analyses. Outcomes included memory, processing speed and dementia incidence. Cardiovascular and cerebrovascular diseases emerged as potential mediators, while mental health, sleep and lung function also showed possible mediating roles. Most studies had some risk of bias, and the authors called for more rigorous causal mediation analyses and standardized reporting.

Key findings

• The review included 16 studies and 72 unique exposure–mediator–outcome associations involving six pollutants.
• PM2.5 was the most studied pollutant, accounting for 65% of analyses.
• Cardiovascular and cerebrovascular diseases emerged as potential mediators; mental health, sleep and lung function also showed mediating potential.
• Most studies had some risk of bias, particularly in outcome assessment and confounding adjustment.

Why it matters

Understanding pathways linking air pollution with cognitive aging may help clarify how exposure relates to outcomes such as memory decline and dementia, and could inform future preventive research. The review suggests vascular conditions may be important intermediates, but evidence for this and other proposed pathways remains uncertain. Better causal analyses and consistent reporting are needed before these mechanisms can be established.

What to keep in mind

Most included studies had some risk of bias, especially in outcome assessment and confounding adjustment; the review also notes that further research is needed to confirm proposed mediators.