NeuralCipher Research overview
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BackgroundParkinson's disease (PD), multiple sclerosis (MS) and motor neurone disease (MND) are progressive and debilitating diseases that are increasing in prevalence globally. Some primary studies show an increased risk from long-term outdoor air pollution exposure, while others contradict this association.MethodsA systematic review and meta-analysis were undertaken to assess the associations of long-term (≥1 year) outdoor air pollution exposure with PD, MS and MND incidence. We searched eight databases for publications up to July 2025. Primary case-control, cohort, cross-sectional or ecological studies investigating the association between long-term air pollution exposure and adult (>18 years old) PD, MS, or MND incidence were included. Meta-analyses were carried out using random-effects models with assessment of heterogeneity, meta-bias and shape of the exposure-response functions. PROSPERO (CRD42023417961).ResultsOf 42 papers included, 26, 3 and 3 were meta-analysed for PD, MS, and MND outcomes, respectively. 19 studies from North America, 12 from Europe and 10 from Asia were meta-analysed. For every 5 μg/m3 and 15 μg/m3 increase of Particulate Matter 2.5 (PM2.5) and PM10 concentration, estimated (95% Confidence Interval) PD risk was 10% (1.10; 1.03-1.19) and 18% (1.18; 1.01-1.38), respectively but effects varied across settings (Prediction Interval: 0.80-1.52 for PM2.5 and 0.41-3.36 for PM10), with the largest estimated risk for PM2.5 in Asia (1.19; 1.01-1.41). There was no clear evidence that PM2.5 (1.01; 0.77-1.32) or nitrogen dioxide (NO2, 0.98, 95% CI: 0.95-1.01) were associated with MS risk or PM2.5 with MND risk (1.07, 95% CI: 0.86-1.33).ConclusionThis systematic review reports increased PD risk from long-term PM2.5 and PM10 exposure. No association was observed for MS and MND from a very limited evidence base. The neurodegenerative diseases investigated here are rare and therefore alternatives to insufficiently powered cohort studies are needed to strengthen the evidence on risk.
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