According to an extensive new report by the Committee on the Medical Effects of Air Pollutants (COMEAP), air pollution contributes to an acceleration of the cognitive decline often associated with aging and the risk of developing dementia. Experts argue that this is likely caused by tiny toxic particles seeping into the bloodstream from the lungs, irritating blood vessels and disrupting circulation in the brain. Also, in rare cases, extremely small air pollution particles can cross the blood-brain barrier and directly damage neurons.
Scientists have known for decades that air pollutants, by narrowing and thickening blood vessels, can contribute to cardiovascular disease, stroke and other circulatory problems. Eventually, these processes could lead to vascular dementia, a condition caused by damage to the brain’s blood vessels.
“We believe there is a strong case for the effects of air pollutants on the cardiovascular system to have a secondary effect on the brain. We think it is likely that this effect could lead to brain damage,” the report’s authors wrote. “Therefore, we consider the association between air pollutant exposure and effects on cognitive decline and dementia to be likely to be causal in terms of this mechanism.”
According to the researchers, the most dangerous types of air pollutants are probably PM2.5, which have a diameter of less than 2.5 micrometers (about three percent of the width of a human hair). Although only a small proportion of these tiny particles can directly pass the blood-brain barrier, their indirect and prolonged effects can still lead to health problems such as dementia. In addition, air pollution could also stimulate immune cells in the brain, leading to neuronal damage.
“Epidemiological evidence suggests an association between exposure to ambient air pollutants and both the risk of developing dementia and the acceleration of cognitive decline. [However,] the epidemiologic literature is inconsistent as to which pollutant is most associated with these effects,” the authors concluded.
In order to clarify the association between pollution and dementia, more research is needed, including epidemiological studies on cognitive decline and dementia, imaging and pathological studies, as well as research on how the human brain handles different types of particles.
The full 291-page report can be downloaded here.
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By Andrei Ionescu, Earth.com staff writer