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(Stroke. 2007;38:918.)
© 2007 American Heart Association, Inc.

Original Contributions

Associations of Fine and Ultrafine Particulate Air Pollution With Stroke Mortality in an Area of Low Air Pollution Levels

Jaana Kettunen, MSc; Timo Lanki, MSc; Pekka Tiittanen, MSc; Pasi P. Aalto, PhD; Tarja Koskentalo, MSc; Markku Kulmala, PhD; Veikko Salomaa, PhD Juha Pekkanen, MD

From Environmental Epidemiology Unit (J.K., T.L., P.T., J.P.), National Public Health Institute (KTL), Kuopio, Finland; Department of Physical Science (P.P.A., M.K.), University of Helsinki, Finland; Helsinki Metropolitan Area Council (T.K.) (YTV), Helsinki, Finland; Department of Epidemiology and Health Promotion (V.S.), National Public Health Institute (KTL), Helsinki, Finland; and the School of Public Health and Clinical Nutrition (J.P.), University of Kuopio, Finland.

Correspondence to Jaana Kettunen, National Public Health Institute (KTL), Environmental Epidemiology Unit, PO Box 95, FIN-70701 Kuopio, Finland. E-mail jaana.kettunen{at}ktl.fi

Background and Purpose— Daily variation in outdoor concentrations of inhalable particles (PM₁₀ <10 µm in diameter) has been associated with fatal and nonfatal stroke. Toxicological and epidemiological studies suggest that smaller, combustion-related particles are especially harmful. We therefore evaluated the effects of several particle measures including, for the first time to our knowledge, ultrafine particles (<0.1 µm) on stroke.

Methods— Levels of particulate and gaseous air pollution were measured in 1998 to 2004 at central outdoor monitoring sites in Helsinki. Associations between daily levels of air pollutants and deaths caused by stroke among persons aged 65 years or older were evaluated in warm and cold seasons using Poisson regression.

Results— There was a total of 1304 and 1961 deaths from stroke in warm and cold seasons, respectively. During the warm season, there were positive associations of stroke mortality with current- and previous-day levels of fine particles (<2.5 µm, PM_2.5) (6.9%; 95% CI, 0.8% to 13.8%; and 7.4%; 95% CI, 1.3% to 13.8% for an interquartile increase in PM_2.5) and previous-day levels of ultrafine particles (8.5%; 95% CI, –1.2% to 19.1%) and carbon monoxide (8.3; 95% CI, 0.6 to 16.6). Associations for fine particles were mostly independent of other pollutants. There were no associations in the cold season.

Conclusions— Our results suggest that especially PM_2.5, but also ultrafine particles and carbon monoxide, are associated with increased risk of fatal stroke, but only during the warm season. The effect of season might be attributable to seasonal differences in exposure or air pollution mixture.

Key Words: air pollution • epidemiology • mortality • particulate matter • stroke

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