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Intracerebral haemorrhage associated with hourly concentration of ambient particulate matter: case-crossover analysis
  1. S Yamazaki1,
  2. H Nitta2,
  3. M Ono3,
  4. J Green4,
  5. S Fukuhara1
  1. 1Department of Epidemiology and Healthcare Research, Graduate School of Public Health, Kyoto University, Kyoto, Japan
  2. 2Epidemiology and Exposure Assessment Section, National Institute for Environmental Studies, Tsukuba, Japan
  3. 3Environmental Health Sciences Division, National Institute for Environmental Studies, Tsukuba, Japan
  4. 4Graduate School of Medicine, The University of Tokyo, Japan
  1. Correspondence to:
 Dr S Yamazaki
 Department of Epidemiology and Healthcare Research, Graduate School of Public Health, Kyoto University, Yosidakonoe-cho, Sakyo-Ku, Kyoto 606-8501, Japan; yamazaki.shin{at}


Aims: To examine the association of hourly time lagged concentration of ambient particulate matter and death due to stroke.

Methods: Mortality data for five years (January 1990 to December 1994) were obtained from the Ministry of Health, Labour, and Welfare of Japan. Data were used only if the deceased was 65 years old or older at the time of death, if death was attributed to intracerebral haemorrhage or ischaemic stroke, and if the deceased lived in one of 13 major urban areas. Hourly mean concentrations of PM7, NO2, and photochemical oxidants were measured at monitoring stations in the 13 areas. Time stratified case-crossover analysis was used to examine the data for evidence of triggering stroke mortality.

Results: The 1-hour mean concentration of PM7 measured about 2 hours before death was associated with the risk of death due to intracerebral haemorrhage from April to September (odds ratio = 2.40, 95% CI 1.48 to 3.89, for exposure to PM7 of more than 200 μg/m3 (threshold)). The higher risk was independent of the 24-hour mean concentration of PM7. PM7 was not associated with death due to ischaemic stroke.

Conclusions: Transiently high concentrations of PM7 are associated with death due to intracerebral haemorrhage. Air quality standards or guidelines for particulate matter should be based not only on 24-hour mean concentrations, but also on hourly data.

  • air pollution
  • cerebral haemorrhage
  • mortality

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  • Published Online First 17 July 2006

  • Funding: this work was supported in part by the Ministry of the Environment, Japan

  • Competing interests: none

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