Two studies published this year by researchers at six universities and the National Institute on Aging provide the first evidence of such benefits in an older population.
One report, published in the Proceedings of the National Academy of Sciences, found that the risk of dementia declined significantly in women 74 and older following a decade-long reduction in two types of air pollution: nitrogen dioxide, a gaseous by-product of emissions from motor vehicles, industrial sources, and natural events such as wildfires; and fine particulate matter, a mix of extremely small solids and liquids arising from similar sources.
A second report in PLOS Medicine, relying on the same sample of more than 2,200 older women, found that lower levels of these pollutants were associated with a slower rate of cognitive decline.
There are several theories about how air pollution affects the brain. Extremely tiny particles — a human hair is at least 30 times as large as the largest particle — may travel from the nasal cavities to the brain via the olfactory (smell) system, putting the brain’s immune system on high alert. Or, pollutants may lodge in the lungs, causing an inflammatory response that spreads and leads to the brain.
Also, pollutants can damage the cardiovascular system, which is essential to brain health. (Links between air pollution, stroke, and heart disease are well established.) Or tiny particles can cross the blood-brain barrier, wreaking direct damage. And oxidative stress may occur, releasing free radicals that damage cells and tissue.
