Middle-aged and older adults who breathe polluted air in towns and cities can be at increased risk of dementia and strokes, researchers have warned.
Normal pollution levels – fine particles from traffic fumes, factory and power station emissions and wood fire smoke – in major cities caused hidden brain strokes while shrinking the brain by the equivalent of one year’s worth of ageing, they said.
This “fine particulate matter” with a diameter of 2.5 millionth of a metre, known as PM2.5, travels deep into the lungs and previous research has linked it to strokes and heart attacks.
Now a new study has shown long-term exposure to these airborne pollutants can cause damage to brain structures and impair thinking and memory abilities in middle-aged and older adults.
It found evidence of smaller brain structure and a type of “silent” ischemic stroke, resulting from a blockage in the blood vessels supplying the brain, in more than 900 patients taking part in a heart study.
Researchers looked at how far the patients aged over 60 who did not have a stroke or dementia lived from busy roads.
They then used satellite images to assess prolonged exposure to ambient PM2.5.
Dr Elissa Wilker, a researcher in the cardiovascular epidemiology research unit at the Beth Israel Deaconess Medical Centre in Boston in the US, said: “This is one of the first studies to look at the relationship between ambient air pollution and brain structure. Our findings suggest that air pollution is associated with insidious effects on structural brain ageing, even in dementia and stroke-free individuals.”
The evaluation included total cerebral brain volume, a marker of age-associated brain atrophy; hippocampal volume, which reflects changes in the area of the brain that controls memory; and white matter volume, which can be used as a measure of pathology and ageing.
The study, published in the journal Stroke, found that an increase of only two microgrammes per cubic metre of air in PM2.5, a range commonly observed across US cities, was associated with being more likely to have ischemic stroke and smaller cerebral brain volume, equivalent to approximately one year of brain ageing.
Dr Wilker added: “These results are an important step in helping us learn what is going on in the brain.
“The mechanisms through which air pollution may affect brain ageing remain unclear, but systemic inflammation resulting from the deposit of fine particles in the lungs is likely important.”
Dr Sudha Seshadri, professor of neurology at Boston University School of Medicine, said: “This study shows that for a two microgramme per cubic metre of air increase in PM2.5, a range commonly observed across major US cities, on average participants who lived in more polluted areas had the brain volume of someone a year older than participants who lived in less polluted areas. They also had a 46 per cent higher risk of silent strokes on MRI.
“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 more at the impact of air pollution over a longer period; its effect on more sensitive MRI measures [and] on brain shrinkage over time; and other risks including of stroke and dementia.”