Air pollution is linked to an increased risk of stroke, a large global study in the British Medical Journal suggests.
Scientists say even short-term spikes in pollution were mirrored by a rise in strokes – particularly in low and middle-income countries.
The work builds on earlier studies linking pollution to cardiovascular risk.
UK experts say although pollution is lower in the developed world, it may still pose a significant risk.
Parts of the UK are breaching pollution limits set by the European Union in 2010.
And the UK government says some major cities may well continue to do so until at least 2025.
The European Environment Agency warns that air pollution can lead to major illness and contribute to premature deaths.
The latest study looked specifically at the risk of stroke. Scientists from Edinburgh University scoured the results of 94 studies covering 28 countries across the world.
They say the trends were consistent – a short-term rise in pollution was associated with a rise in the number of people admitted to hospital for strokes and in stroke deaths.
The link was the strongest in low and middle-income countries and on the day people were exposed to high pollution.
The review looked at a range of possible pollutants – from gases such as sulphur dioxide, nitrogen dioxide and carbon monoxide to fine soot particles known as PM 2.5.
Dr Anoop Shah, lead author of the study, said: “This study now demonstrates that even short-term exposure to air pollution can trigger disabling strokes or death from stroke.
“One of the key differences between risk of stroke due to air pollution and other risk factors such as smoking or high blood pressure is that the whole general population is exposed.
“As such, this increased risk of stroke is in the general population and not just those previously thought to be at high risk.”
But Dr Shamim Quadir at the Stroke Association said more work was needed to establish how strong this link is and whether or not air pollution could be considered as a risk factor for stroke.
The British Heart Foundation, which funded the study, says there is an urgent need for the UK government to meet pollution targets.
It says failure to do so could be putting hundreds of thousands of people at risk – though further research is needed to confirm this estimate.
The charity suggests people with heart conditions or lung disease should monitor air pollution where they live and work.
Story courtesy of BBC News