Finland — Low environmental levels of fine and ultrafine particulate matter,as well as carbon dioxide, increase the risk of stroke, but the heightened riskoccurs only during warm weather months, Finnish researchers report.
Previous research has linked air pollution with a higher risk of fatal andnonfatal stroke, according to a report in the rapid access issue of the journalStroke. However, the Finnish study is the first, to the authors’ knowledge, toexamine the impact on stroke risk of ultrafine particulate pollution, defined asmolecules with a diameter of less than 2.5 microns.
Dr. Jaana Kettunen, from the National Public Health Institute in Kuopio, andcolleagues compared air pollution levels from 1998 to 2004 with the number ofstroke deaths among elderly subjects living in Helsinki, a city known to haverelatively little air pollution.
A total of 1,304 stroke deaths in the warm season and 1,961 in the coldseason were logged in during the study period.
During the warm season, every 6 microgram per cubic meter increase incurrent-day levels of fine particulate air pollution was associated with a 6.9percent increase in deaths from stroke. The corresponding stroke death rate forprevious-day fine particulate increases was 7.4 percent. However, particulateair pollution had no effect on stroke during the cold season.
Previous-day levels of ultrafine particles plus carbon monoxide were alsolinked to stroke mortality. However, Kettunen commented in a statement, “theseassociations were less robust” than those seen with fine particulatepollution. “Coarse particles were not statistically significantlyassociated with stroke deaths,” she added.
“Our results suggest that the levels of combustion-originating particlesrather than coarse particles explain the association between particulate matterand stroke,” the authors conclude. “Thus, regulatory efforts should befocused on reducing emissions of combustion particles.”