Size of air pollution particles affects risk of death from stroke

The size of air pollution particles may affect a person’s risk of dying from a stroke, according to new research.

The study compared submicron particulate matter (PM1), fine particulate matter (PM2.5) and respirable particulate matter (PM10), using electronic medical records in China to identify over 3.1 million hospitalizations for stroke.

After adjusting for factors such as age, sex, socioeconomic status, diabetes and high blood pressure, researchers found each 10 μg/m3 increase in annual average exposure to particulate matter was associated with increased risk of dying of stroke when hospitalized, with a 24% greater risk for exposure to PM1, an 11% greater risk from PM2.5, and a 9% greater risk from PM10.

The risks were stronger in people with ischemic stroke, caused by a blood clot, than in people with hemorrhagic stroke, caused by bleeding in the brain. The greatest risk of death from stroke was in people with ischemic stroke and exposure to the smallest air pollution particles, PM1.

Yet researchers also found that a reduction in PM10 would have the largest impact on reducing overall deaths from stroke, reducing the number of hospital deaths by 10% for short-term exposure and 21% for long-term exposure.

‘Air pollution has been previously linked to a greater risk of stroke, and stroke is a leading cause of death worldwide,’ said study author Hualiang Lin, PhD, of Sun Yat-sen University in Guangzhou, China. ‘What is lesser known is how the different sizes of particulate matter affect that risk. Our research found that the size of air pollution particles may affect a person’s risk of dying from stroke.’

Researchers identified individual levels of air pollution exposure for each participant by using their home addresses and an air pollution data source that records daily concentrations of different types of particulate matter.

Lin said it is important to note that the study results do not prove that air pollution causes stroke deaths, they only show an association.

‘Our study includes measurements of PM1, which may be small enough to be inhaled deeply into lungs, pass through lung tissue, and circulate in the bloodstream,’ said Lin. ‘Obtaining a deeper understanding of the risk factors of all particulate matter sizes and the magnitude of their possible effects may help reduce the number of deaths and improve the outcomes for people with stroke.’

The study has been published in an online issue of Neurology, the medical journal of the American Academy of Neurology.

Photo by Robina Weermeijer