Pollution, Particles, and Dementia: A Hypothetical Causative Pathway
Department of Environmental Medicine, Aberdeen University, Aberdeen AB25 2ZP, UK
Institute of Occupational Medicine, Edinburgh EH14 4AP, UK
Department of Public Health, Wolverhampton University, Wolverhampton WV1 1LY, UK
Department of Environmental Science, Birmingham University, Birmingham B15 2TT, UK
Department of Mental Health, Aberdeen University, Aberdeen, EH14 4AP, UK
Author to whom correspondence should be addressed.
Int. J. Environ. Res. Public Health 2020, 17(3), 862; https://doi.org/10.3390/ijerph17030862
Received: 31 December 2019 / Revised: 24 January 2020 / Accepted: 25 January 2020 / Published: 30 January 2020
(This article belongs to the Special Issue Global Public Health and Epidemiology)
Epidemiological studies of air pollution have shown associations between exposure to particles and dementia. The mechanism of this is unclear. As these seem unlikely in terms of the very small dose likely to reach the brain in usual Western urban circumstances, we extend our 1995 hypothetical explanation of the association of air pollution with cardiac deaths as a plausible alternative explanation of its associations with dementia. Since our original proposal, it has become apparent that inflammation may be carried by blood from organ to organ by biologic microparticles derived from cell membranes. These transmit inflammatory messages to endothelial cells throughout the body as part of a general defensive response to assumed bacterial infection; particulate air pollution has recently been shown to be associated with their release into the blood. We propose that episodic release of biologic microparticles from pollution-induced lung inflammation causes secondary inflammation in the blood-brain barrier and cerebral microbleeds, culminating over time in cognitive impairment. Ultimately, by incomplete repair and accumulation of amyloid, this increases the risk of Alzheimer’s disease. Importantly, this mechanism may also explain the relationships of other inflammatory conditions and environmental factors with cognitive decline, and point to new opportunities to understand and prevent dementia.