Recent exposure to air pollution is linked to an increased risk of stroke, according to new research.
Researchers found a strong association between the levels of pollutants in the air and the number of people suffering a major stroke within days of exposure.
Their findings add to previous reports that long term exposure to air pollution is linked to lung, heart and circulatory diseases.
The team - led by Edinburgh researchers - analysed data from 103 studies across 28 countries, involving six million people.
They looked at exposure to polluting gases - such as carbon monoxide, sulphur dioxide and nitrogen dioxide - as well as microscopic soot particles in the air, known as PM2.5 and PM10.
Their findings reveal that even short-term exposure to these air pollutants increased the risk of hospitalisation or death from stroke in the following seven days.
The strongest adverse effects were seen on the same day of exposure to PM2.5 - particles that are 50,000 times smaller than the thickness of a human hair, which float unseen in the air.
A person’s risk of stroke increases by one percent for every extra ten microgrammes of PM2.5 in a cubic metre of air, according to the study.
The legal limit in Europe is 25 microgrammes per cubic metre but in the most polluted areas, such as central London, pollution can rise as high as 50 microgrammes per cubic metre in a 24 hour period. This would raise stroke risk by five per cent for everybody living in those areas.
The increased risk is low compared to other risk factors - such as smoking and high blood pressure - but the concern is that the whole population is exposed.
Improving air quality could help to reduce the burden of stroke in countries around the world, researchers say.
This study now demonstrates that even short-term exposure to air pollution can trigger disabling strokes or death from stroke. We hope these findings further highlight the adverse effects of pollution on health and policies will be put in place to continue to reduce atmospheric air pollution.
Strokes occur when the blood supply to part of the brain is cut off, causing brain cells to become damaged or die. It is a leading cause of disability worldwide and causes more than 40,000 deaths in the UK each year.
It is commonly caused by coronary heart disease and common risk factors include obesity, smoking and high blood pressure. Until now, there has been limited evidence for the effect of short term air pollution on stroke risk.