Evidence is accumulating that breathing in very small particles (Fine particulate matter PM2.5) over a long time is associated with an increased risk of dementia. The association suggests that the particles may actually be a cause of dementia, perhaps especially if the particles are coated with neurotoxic chemicals. These particles come from traffic (diesel more than petrol-powered vehicles), coal-fired power plants, agricultural emissions, and bush fires (US ‘wildfires’). It’s thought that the particles can enter the brain via the olfactory nerve in the nose which connects directly to the brain following the path available for large molecules such as pheromones. These particles, and the inflammatory products they trigger may usually be cleared from the brain by the ‘glymphatic’ system. Problems with that system (e.g. due to obstructive sleep apnoea) have also been shown to be associated with higher risk of dementia.

Exposure to these particles is associated with many other poor health outcomes.

I wrote a post about Alzheimer’s disease and pollution in May 2020, and about the glymphatic system in May 2021.