Air pollution could result in brain damage affecting cognitive function, according to a new study. These changes have been observed in middle-aged and older adults exposed to even moderate levels of pollution throughout the nation.

Beth Israel Deaconess Medical Center researchers, together with colleagues from the Boston University School of Medicine, examined records of more than 900 patients who participated in the Framingham Heart Study.

"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," said Sudha Seshadri from Boston University School of Medicine.

Researchers noted the distance participants lived from major roadways, as well as data from satellite images revealing the presence of particulate matter in the air. Material known as PM2.5 – particles under 2.5 microns (roughly 1/100,000 inch), which can result in significant lung damage – was of particular interest to investigators. This information was then compared to health records, including incidence of stroke in the subjects.

The study revealed a correlation between levels of air pollution and a form of silent ischemic stroke, caused by a blood clot. Silent strokes occur without the affected person's knowledge. The subjects in the study were all at least 60 years old and had no previous record of stroke or dementia. The examination detailed the volume of the hippocampus, associated with memory, as well as total brain size and the quantity of white brain matter, which tends to mark aging.

Atmospheric pollution of PM2.5 material can be caused by the burning of wood, by automobiles, factories and power plants. These tiny pieces of debris can penetrate deep into lungs, resulting in strokes and cardiac arrests. Researchers found that PM2.5 particulate matter levels equivalent to those found in the air over metropolitan areas of New York and New England result in an increase of infarcts and lower brain volumes similar to those in patients one year older than the subjects. Investigators are uncertain how air pollution can affect the brain, but they theorized the material could drive inflammation, which has been linked to reduced brain volume.

One of the shortcomings of the current study is that it was a cross-sectional study, only examining subjects at a single point in time. A longer longitudinal study, examining patients over a period of time, would be needed to provide direct evidence that air pollution can result in damages to the brain, including reductions in brain size and silent strokes.

The examination of possible brain damage caused by air pollution was detailed in the journal Stroke.

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