NEUROTOXIC SMOG: A SYSTEMATIC REVIEW AND META-ANALYSIS OF LONG-TERM AMBIENT AIR POLLUTION EXPOSURE'S IMPACT ON MRI BIOMARKERS OF BRAIN STRUCTURE

Abstract

Introduction: Air pollution is a major global health threat, linked to millions of deaths and a rising burden of cognitive decline. Long-term exposure to PM2.5 is associated with increased risk of Alzheimer’s disease, vascular dementia, and stroke, highlighting the need to identify which brain regions are most affected. This study aims to investigate the impact of chronic smog exposure on specific brain structures by analyzing MRI-detectable markers of neurodegeneration.

Method: This meta-analysis assessed the association between long-term ambient air pollution exposure and structural brain changes, specifically focusing on neuroimaging markers. A literature search was conducted across databases like Pubmed, Google Scholars, DOAJ until March 11, 2025, using keywords such as ‘neuroimaging,’ ‘white matter,’ ‘ambient air pollution,’ and ‘brain volume changes.’ Cross-sectional studies were included. Study quality was evaluated using the ROBINS-I tool, and statistical analysis was conducted using R. The study protocol was registered on PROSPERO (CRD420251030714).

Results: Out of 173 screened studies, 9 were eligible for inclusion. The pooled analysis of air pollution and white matter hyperintensity (WMH) revealed a significant association, with an odds ratio (OR) of 1.40 (95%CI: 1.27–1.54), indicating a strong link between air pollution and WMH. No significant heterogeneity was observed (p = 0.55). Subgroup analysis showed that PM2.5 exposure significantly increased WMH (OR = 1.39, 95%CI: 1.21–1.61). For brain volume, the analysis demonstrated a significant reduction associated with air pollution (OR = 0.8659, 95%CI: 0.8300–0.9033). The regression test for funnel plot asymmetry showed no significant bias (z = 0.9684, p = 0.3329). Air pollution was positively correlated with WMH (r = 0.62) and negatively with cognitive function (r = –0.95).

Conclusion: Chronic air pollution exposure is strongly linked to white matter damage, brain atrophy, and cognitive decline, underscoring its role in accelerating neurodegeneration and the urgent need for targeted public health interventions.