City air damages the brain

Higher levels of fine particulate matter in cities cause the human brain volume to shrink and increase the risk of silent strokes, according to a study published in latest issue of Stroke. Such changes to the brain structure can result in dementia, depression and impaired cognitive function.

Particulate matter increases the risk of strokes. (Photo credit: D€NNI$, flickr)

Particulate matter increases the risk of strokes. (Photo credit: D€NNI$, flickr)

According to the latest report from the European Environment Agency (EEA), fine particulate manner is responsible for 430,000 premature deaths annually in Europe alone.

Until recently scientists tended to examine only the link between air pollution and lung diseases. But Elissa Wilker from the Beth Israel Deaconess Medical Center in Boston and her colleagues have now determined that fine particulate matter not only impairs the respiratory system, it even has an impact on the human brain structure.

Brain ages faster

The researchers studied more than 900 participants ages 60 years and up living various distances from major roadways and therefore exposed to different levels of fine particulate matter.

The researchers conducted brain scans on their subjects to determine total cerebral brain volume. The results revealed that subjects exposed to higher levels of fine particulate matter had on average a significantly smaller brain volume.

Decreased brain volume is a natural part of the aging process that has an impact on mental performance and learning ability. But as the study showed, increased exposure to fine particulate matter intensifies this effect: for every increase of 2 micrograms of fine particulate matter per cubic metre of air, brain volume was smaller by 0.32 per cent. This is equivalent to approximately one year of brain aging.

More silent strokes

The study also showed that people who are regularly exposed to increased levels of fine particulate matter have a higher risk of so-called silent strokes – small strokes in which the patients are typically unaware that they have suffered a stroke because they do not experience any outward symptoms.

The team at the Boston clinic found a linear relationship between fine particulate matter and silent strokes: a 46 per cent higher risk of silent strokes on MRI for every 2 micrograms per cubic metre of air increase in fine particulate matter.

Increased dementia, strokes and depression

“This is one of the first studies to look at the relationship between ambient air pollution and brain structure,” says Elissa Wilker. “Our findings suggest that air pollution is associated with insidious effects on structural brain aging, even in dementia- and stroke-free individuals.”

The study, which was published in the May issue of Stroke, demonstrates that the range of fine particulate matter commonly observed across major US cities is causing the brain to age. And yet precisely which mechanism is behind these changes to the human brain structure remains unclear.

“Systemic inflammation resulting from the deposit of fine particles in the lungs is likely important,” says Wilker.


Fine particulate matter

Particulate matter is the term used for the solid particles and liquid droplets found in the air. A type of air pollution, it can come from natural processes such as forest fires, but is oftentimes produced from human activities such as industrial smokestacks, agricultural practices, car emissions and even stoves.

Until the 1980s, only the total amount of particulate matter was measured. Then in 1987, the U.S. Environmental Protection Agency introduced the term fine particulate matter to examine the class of particles that are small enough to be inhaled and remain lodged in the body, either in the mucous membranes of the nose or throat or in the hairs in the nose. Once inside the body they reach the lower respiratory tract and cause adverse health effects.


Photo credit: D€NNI$, flickr/Creative Commons

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