Exercise Under Particulate Matter Exposure: Neurotrophic Responses and Functional Brain Outcomes

Whether particulate matter (PM) exposure modifies the brain-related benefits of exercise remains unresolved. This focused narrative review examined exercise-related neurotrophic responses, centred on brain-derived neurotrophic factor (BDNF), alongside cognitive and brain outcomes under particulate or traffic-related pollution. PubMed and Web of Science Core Collection were searched, and 37 reports, comprising 33 main and four indirect reports, were synthesised by biological outcome level and response pattern. Circulating BDNF responses were heterogeneous; vascular endothelial growth factor (VEGF) and insulin-like growth factor 1 (IGF-1) provided complementary peripheral evidence. Human experiments and population studies reported attenuation in selected cognitive, dementia and imaging contrasts, alongside retained favourable activity associations, uncertain modification and potential activity-related buffering. Central molecular evidence from inhalation experiments was limited; selected animal improvements arose after intravenous particle administration or in an airway-instillation model with cerebral ischaemia/reperfusion, constraining translation to exercise during ambient inhalation. Differences in comparators, interaction scales and exposure measurement, together with potentially overlapping cohorts, limited inference. Neurotrophic and functional findings should be interpreted in relation to the measured outcome and study comparison: a change in peripheral BDNF alone does not establish brain benefit under PM exposure. The evidence supports neither a uniform loss of exercise benefit nor a general concentration threshold for reversal to harm. Studies measuring neurotrophic markers and central or functional outcomes together, with activity-specific exposure and exercise-intensity assessment and appropriate exposure-by-exercise comparisons, are needed to test how these responses relate.