Air pollution could affect trajectory of stroke

Air pollution has previously been associated with an increased risk of stroke, but what about its impact on the trajectory of a stroke once it occurs? This was the subject of a recent study from Chinese and US researchers, who published their results in the journal Neurology.

The study involved 318,752 people in the UK Biobank database with an average age of 56 who did not have a history of stroke or heart disease at the start of the study. Researchers looked at people’s exposure to air pollution based on where they lived at the start of the study and the participants were followed for an average of 12 years. During that time, 5967 people had a stroke. Of those, 2985 people developed cardiovascular diseases and 1020 people later died. People exposed to high levels of air pollution were more likely to have a first stroke, post-stroke cardiovascular disease or death than people not exposed to high levels of pollution.

After adjusting for other factors that could play a role, such as smoking and physical activity level, researchers found that for each 5 µg/m³ increase of fine particulate matter (PM2.5, which includes fly ash from coal combustion), the risk of transitioning from being healthy to having a first stroke increased by 24% and from being healthy to dying the risk increased by 30%. Those who had a stroke during the study had an average exposure of 10.03 µg/m³ of PM2.5, compared to 9.97 µg/m³ for those who did not have a stroke. The researchers also found that the pollutants nitrogen oxide and nitrogen dioxide were associated with an increased risk of stroke and death.

“We found that high levels of air pollution were associated with increased risks of transitions from being healthy to a first stroke, cardiovascular events after stroke and death, but with a stronger effect on the transition from being healthy to having a stroke,” said study author Dr Hualiang Lin, from Sun Yat-sen University. “These results indicate that understanding and reducing the effects of air pollutants on different transition stages in stroke will be beneficial in managing people’s health and preventing the occurrence and progression of stroke.

“More research is needed, but it’s possible that decreasing exposure to heavy levels of air pollution could play a role in reducing the progression of stroke. People can reduce their exposure by staying indoors on heavy-pollution days, reducing their outdoor exercise, wearing masks to filter out particulate matter and using air purifiers.”

Lin noted that the results do not prove that air pollution causes stroke, cardiovascular disease or death; they only show an association. A limitation of the study was that air pollution exposure was assessed only at the beginning of the study and only based on where participants lived.

Image credit: iStock.com/Tunatura

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