Polluted air might increase stroke risk

The risk of death due to stroke is associated with exposure to high concentrations of air pollution about 2 hours before death, Japanese investigators report.

Because this risk appears to be independent of 24-hour particulate matter levels, they suggest that air quality standards be based on hourly data, as well as 24-hour levels.

Particulate matter, or PM, is the term used to describe the tiny particles emitted by automobiles, especially diesel vehicles, informs Reuters.

According to Forbes, the researchers tracked levels of air pollutants -- including nitrogen dioxide, particulate matter, and photochemical oxidants -- on an hourly basis in each of the 13 areas.

They found that between the months of April and September, the risk of hemorrhagic stroke -- when a blood vessel bursts in the brain -- more than doubled two hours after high hourly rates of particulate matter (in excess of 200 micrograms per cubic meter) were observed.

This effect was not found for ischemic stroke, when arteries in the brain become blocked. The researchers propose this may be because the time lag between the start of an ischemic stroke is longer than that for a hemorrhagic stroke.

Previous research showed that the effects of air pollution act quickly on the body, the authors said, with inhaled particles detectable in the blood within 60 seconds.