HEADLINES:
R/€ Air pollution could be stroke of bad luck
September 23, 2006 Edition 1
The risk of death from a stroke is linked to exposure to high concentrations of air pollution two hours before death, Japanese scientists say.
Because this risk appears to be independent of 24-hour particulate matter levels, they suggest air quality standards be based on hourly data.
Particulate matter, or PM, is the term used to describe the tiny particles emitted by cars, especially diesel ones.
Dr Shin Yamazaki of Kyoto University, and associates collected data from the 13 largest cities in Japan regarding concentrations of suspended PM and ambient temperature from 1990 to 1994.
During that period, 17 354 residents age 65 or older died from haemorrhagic strokes, and 46 370 died from ischaemic strokes, the type caused by blood clots.
According to their analyses in the journal Occupational and Environmental Medicine, the odds ratio of death from ischaemic stroke was increased with temperatures above 30°C. In contrast, the risk of death due to bleeding in the brain was higher in cold weather.
However, during summer, high one-hour concentrations of PM7 increased the risk of death from haemorrhagic stroke 2,4-fold, an association independent of 24-hour PM7 concentrations. Death due to ischaemic stroke was not associated with one-hour PM7 levels.
Yamazaki's team suggest this discrepancy may be due to the longer interval from ischaemic stroke onset to death, or to the fact that inhaled particles raise blood pressure, a risk factor for bleeding in the brain.
They propose that, if hourly measures of air quality are unavailable, stricter standards for 24-hour mean levels of suspended particulate matter may be an effective substitute. - Reuters
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