A stroke can cause lasting brain damage, long-term disability, or even death.
Short-term exposure to air pollution may be linked to an increased risk of stroke, according to a study.
The meta-analysis, published recently in the journal Neurology, defined short-term exposure as occurring within five days of the stroke.
A stroke can cause lasting brain damage, long-term disability, or even death. Signs of a stroke can range from mild weakness to paralysis or numbness on one side of the face or body.
"Previous research has established a connection between long-term exposure to air pollution and an increased risk of stroke," said study author Ahmad Toubasi, from the University of Jordan in Amman.
"However, the correlation between short-term exposure to air pollution and stroke had been less clear. For our study, instead of looking at weeks or months of exposure, we looked at just five days and found a link between short-term exposure to air pollution and an increased risk of stroke," Toubasi said.
The analysis involved a review of 110 studies that included more than 18 million cases of stroke. Researchers looked at pollutants such as nitrogen dioxide, ozone, carbon monoxide and sulfur dioxide.
They also looked at different sizes of particulate matter, including PM1, which is air pollution that is less than 1 micron (μm) in diameter, as well as PM2.5 and PM10.
PM2.5 or smaller includes inhalable particles from motor vehicle exhaust, the burning of fuels by power plants and other industries as well as forest and grass fires. PM10 includes dust from roads and construction sites.
People who had exposure to a higher concentration of various types of air pollution had an increased risk of stroke.
Higher concentrations of nitrogen dioxide were linked to a 28 per cent increased risk of stroke and higher ozone levels were linked to a 5 per cent increase, the researchers said.
Carbon monoxide had a 26 per cent increased risk and sulfur dioxide had a 15 per cent increase, they said.
The study found that a higher concentration of PM1 was linked to a 9 per cent increased risk of stroke, with PM2.5 at 15 per cent and PM10 at 14 per cent.
Higher levels of air pollution were also linked to a higher risk of death from stroke, according to the researchers.
Higher concentrations of nitrogen dioxide were linked to a 33 per cent increased risk of death from stroke, sulfur dioxide, a 60 per cent increase, PM2.5, a 9 per cent increase and PM10, a 2 per cent increase, they said.
"There is a strong and significant association between air pollution and the occurrence of stroke as well as death from stroke within five days of exposure," Toubasi said.
"This highlights the importance of global efforts to create policies that reduce air pollution. Doing so may reduce the number of strokes and their consequences," the researcher added.
The authors of the study acknowledged some limitations of the study was most of the research articles included were conducted in high-income countries, while limited data was available from low- and middle-income countries.