Meta-analysis reveals link with long-term exposure to fine particulate matter, nitrogen dioxide, and black carbon
TUESDAY, July 29, 2025 (HealthDay News) — Long-term exposure to outdoor air pollution may increase the risk for dementia, according to a review published online July 24 in The Lancet Planetary Health.
Clare B. Best Rogowski, from the University of Cambridge in the United Kingdom, and colleagues conducted a systematic literature review and meta-analysis to assess the link between outdoor air pollution and the risk for dementia.
Based on 32 included studies, the researchers found that a dementia diagnosis was significantly associated with long-term exposure to fine particulate matter (PM2.5; 21 studies, about 24 million people; pooled adjusted hazard ratio [HR] per 5 μg/m3 increase in exposure, 1.08; 95 percent confidence interval [CI], 1.02 to 1.14; I2 = 95 percent); nitrogen dioxide (16 studies, about 17.2 million people; pooled adjusted HR per 10 μg/m3 increase, 1.03; 95 percent CI, 1.01 to 1.05; I2 = 84 percent); and black carbon/PM2.5 absorbance (six studies, about 19.4 million people; pooled adjusted HR per 1 μg/m3 increase, 1.13; 95 percent CI, 1.01 to 1.27; I2 = 97 percent). There was no significant association seen for exposure to nitrogen oxides (five studies, 241,409 people; pooled adjusted HR per 10 μg/m3 increase, 1.05; 95 percent CI, 0.97 to 1.13; I2 = 44 percent); PM10 (four studies, 246,440 people; pooled adjusted HR per 15 μg/m3 increase, 1.52; 95 percent CI, 0.80 to 2.87; I2 = 82 percent); or annual ozone (four studies, 419,972 people; pooled adjusted HR per 45 μg/m3 increase, 0.82; 95 percent CI, 0.35 to 1.92; I2 = 69 percent), with moderate to considerable heterogeneity between studies in these pooled analyses. Overall, the certainty of evidence of studies was moderate.
“Efforts to reduce exposure to these key pollutants are likely to help reduce the burden of dementia on society,” Rogowski said in a statement. “Stricter limits for several pollutants are likely to be necessary targeting major contributors such as the transport and industry sectors.”
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