Global ambient particulate matter pollution and neurodegenerative disorders: a systematic review of literature and meta-analysis

Previous studies on particulate matter (PM) exposure and neurodegenerative disorders showed inconsistent results, and few studies systematically examined the long-term effect of PM on neurodegenerative diseases, including all-cause dementia, Alzheimer’s disease, Parkinson’s disease, vascular dementia, amyotrophic lateral sclerosis, and cognitive function decline. We systematically searched for published studies in PubMed, Embase, Cochrane Library, and Web of Science up to October 31, 2022. To facilitate a comparison of effect sizes from different studies, we standardized units across studies to a 10 μg/m3 increase for PM. Heterogeneity was assessed by Cochran’s Q test and I2 statistic. Publication bias was evaluated using funnel plots and Egger’s tests. Subgroup analysis, meta-regression, and sensitivity analysis were performed. The protocol for this review was registered with PROSPERO (CRD42021277112). Of the 3403 originally identified studies, a meta-analysis was finally performed in 49 studies. The results showed that there was a significant positive association between long-term PM2.5 exposure and all-cause dementia, Alzheimer’s disease as well as Parkinson’s disease, with pooled OR of 1.30 (95%CI: 1.14, 1.47, I2 = 99.3%), 1.65 (95%CI: 1.37, 1.94, I2 = 98.2%), and 1.17 (95%CI: 1.00, 1.33, I2 = 91.8%). A positive association between PM10 and vascular dementia was observed (OR = 1.12, 95%CI: 1.04, 1.21, I2 = 0.0%). Association between PM exposure and decreased cognitive function score was found. Our results highlight the important role of PM pollution, particularly PM2.5, in the risk of age-related neurodegenerative diseases and cognitive function decline.