Environment International · Jun 20, 2026

Association of long-term outdoor air pollution exposure with incidence of Parkinson's disease, multiple sclerosis and motor neuron diseases: a systematic review and meta-analysis

By Tien-Smith AZ, Absar S, Rogowski CB et al.

BACKGROUND: Parkinson'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. METHODS: A 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). RESULTS: Of 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). CONCLUSION: This 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.

doi.org/10.1016/j.envint.2026.110377Open accessPubMed 42420066Populations