AIr Pollution and Accelerated Cognitive Decline: Implications for Alzheimer's Disease Progression a Systematic Review (2020–2025)

Background: Fine particulate matter (PM₂. ₅) is now recognized as one of the most harmful urban environmental exposures for brain health. Objective: This systematic review synthesizes evidence from 2020–2025 linking long-term PM₂. ₅ exposure to accelerated cognitive decline and Alzheimer’s disease (AD) progression. Methods: PRISMA 2020-compliant search of PubMed, Scopus, Web of Science, and Embase (Jan 2020Oct 2025). Included studies quantified PM₂. ₅ exposure and reported AD-related outcomes (cognition, biomarkers, imaging, and pathology). Quality was assessed using the Newcastle-Ottawa Scale and SYRCLE tool. Results: Twenty-eight studies (17 human cohorts, 11 preclinical) were included. A 10 µg/m³ increase in PM₂. ₅ was associated with 12–34% higher dementia incidence [1-4] and faster Aβ/tau accumulation [5-8]. Key mechanisms comprised olfactory translocation, blood- brain barrier disruption, oxidative stress, and chronic neuroinflammation [9-14]. Effects were amplified in APOE ε4 carriers [15, 16]. Conclusion: PM₂. ₅ is a potent, modifiable accelerator of sporadic AD. Urgent air-quality policies and personal protection strategies are needed.