Smog pollutant may be tied to stroke risk

People who live in areas with high levels of traffic-related air pollution might have a slightly increased risk of dying from stroke, Danish researchers suggest in a new study.
They found people living in urban zones with high estimated concentrations of nitrogen dioxide were 22 percent more likely to suffer a fatal stroke than people in less-polluted neighbourhoods.
Nitrogen dioxide is a component of car exhaust and is known to cause lung damage. Previous research also suggests spikes in air pollution over the course of days or weeks can trigger death and hospitalisation from stroke.
Last year, the US Environmental Protection Agency strengthened its standards to prevent brief exposures to high levels of the pollutant, but the average threshold has remained the same for decades.
The latest study, published in the journal Stroke, is one of the largest and most comprehensive to link chronic exposure to everyday levels of air pollution to strokes, said Dr Jiu-Chiuan Chen, who studies the effects of air pollution at the University of Southern California Keck School of Medicine in Los Angeles.
"Policy-makers need to realise the danger of living and walking near a high traffic area," said Chen, who was not involved in the new work.
The Danish researchers looked at data for more than 52,000 residents of two major cities in Denmark.
Over the course of a decade, nearly 2,000 participants, aged 50 to 65 at the start of the study, experienced a first-time stroke landing them in the hospital, and 142 died within 30 days.
People exposed to the highest levels of nitrogen dioxide at their homes were five percent more likely to experience a stroke than those who breathed the cleanest air. And they were 22 percent more likely to die from a stroke, report Zorana J. Andersen, of the Danish Cancer Society in Copenhagen, and colleagues.
Those numbers take into account several factors related to stroke risk, such as how heavy people were and whether or not they exercised or smoked.
But from a statistical point of view, it is still possible that chance may have played a role in the findings.
And there is no proof that nitrogen dioxide itself - and not some unknown factor - caused the rise in strokes.