A new paper, recently published in the scientific journal Stroke, begins by stating that while scientists have been long aware of the link between ambient air pollution and cerebrovascular disease, no data exists on whether this is related to structural changes in the brain.
To close this gap, a research team led by scientists from Beth Israel Deaconess Medical Centre and Boston University School of Medicine examined 943 healthy adults (aged 60 and older) who took part in the Farmingham Heart Study, and found that even moderate levels of air pollution lead to a smaller brain volume and higher incidence of covert infarcts – a type of “silent” ischemic stroke resulting from a blockage in the blood vessels supplying the brain.
Silent strokes, while in most cases largely asymptomatic and only detectable via brain scans, are associated with poorer cognitive function and dementia.
“This is one of the first studies to look at the relationship between ambient air pollution and brain structure,” says Elissa Wilker, ScD, a researcher at the Cardiovascular Epidemiology Research Unit at Beth Israel Deaconess Medical Centre. “Our findings suggest that air pollution is associated with insidious effects on structural brain aging, even in dementia- and stroke-free individuals.”
The study assessed how far the participants lived from major roadways and how exposed they were to fine particulate matter, i.e., particles with a diameter of 2.5 millionth of a metre, or PM2.5 for short. These particles come from a variety of sources, such as power plants and car exhaust, and increase one’s risk of cardiovascular events like heart attacks and stroke.
After correlating total cerebral brain volume, a marker of age-associated brain atrophy; hippocampal volume, which reflect changes in the area of the brain that controls memory; white matter hyperintensity volume, which can be used as a measure of pathology and aging; and covert brain infarcts with exposure to pollution, the team found that a 2µg increase of PM2.5 per cubic metre – a range found in most bigger cities – was associated with a 0.32% decrease in brain volume and a 46% in silent stroke incidence.
“This is concerning since we know that silent strokes increase the risk of overt strokes and of developing dementia, walking problems and depression. We now plan to look at more the impact of air pollution over a longer period, its effect on more sensitive MRI measures, on brain shrinkage over time, and other risks including of stroke and dementia.”
The new results may help researchers understand “what could be going on between air pollution and serious outcomes like stroke and cognitive impairment,” Wilker told Live Science. With some proposing inflammation as a possible mechanism behind the effect, current dearth of available data makes it hard for researchers to make any bold claims just yet.