Air Pollution Hikes Stroke Risk

The type of stroke that results when a blood clothemorrhagic stroke, which is caused by bleeding in
travels to the brain -- called an ischemic stroke --the brain, during the same "high pollution" days,
is more likely to occur on days when the airnotes Wellenius, but found no association between
contains a larger concentration of particulatethe two.
matter, according to a study published online inReducing Exposure May Lower Risk
Stroke: Journal of the American Heart Association.The air pollution in question -- particulate matter
Researchers at Beth Israel Deaconess Medicalsmaller than 10 micrometers in diameter --
Center (BIDMC) and the Harvard School of Publicincludes particles from car and truck exhaust,
Health (HSPH) examined air quality on a total ofpower plants and refineries. The measurements
37,000 days in nine cities. Risk of hospitalizationwere provided by the US Environmental
for ischemic stroke was 1 percent higher on daysProtection Agency from nine US cities:
with relatively high levels of air pollution, comparedBirmingham, Ala., Chicago, New Haven, Conn.,
with low-air pollution days, reports lead authorCleveland, Detroit, Minneapolis, Pittsburgh, Salt
Gregory Wellenius, ScD, postdoctoral fellow inLake City and Seattle.
cardiology at BIDMC.The authors analyzed hospital admissions among a
Third Cause of Death in USgroup of Medicare patients with an average age
"Although these effects sound relatively small,"of 79. Seventy-five percent of the patients were
says Wellenius, "given the large number of peoplewhite, and 61 percent were female. Their findings
exposed to air pollution and the large number ofshowed that during the course of their study,
people at risk for stroke .... the actual number ofthere were 155,503 hospital admissions for
strokes could be significant."ischemic stroke.
Stroke is the third leading cause of death in theThe final analysis demonstrated a 1.03 percent
US, affecting more than 700,000 individuals eachrise in ischemic stroke on the days with the
year.highest pollution measures.
A "consistent increased risk" for cardiac health"We don't know exactly what mechanisms are
problems associated with exposure to ambient airinvolved that trigger these cardiac events," says
particles was established in earlier research byWellenius. "However, we do know that particulates
Wellenius and coauthors Murray Mittleman, MD,in the air promote inflammation, which is a
DrPH, of BIDMC's Cardiovascular Epidemiologysignificant risk factor for cardiac events; that
Research Unit and Joel Schwartz, PhD, of HSPH.exposure to particulates can lead to changes in
"Air pollution has been shown to trigger heartheart rate and blood pressure; and that pollution
attacks and to aggravate the conditions ofcan cause changes in coaguable states (related to
patients with congestive heart failure," saysblood clotting abilities)."
Mittleman, who is also an associate professor ofThe authors say that future research will focus
medicine at Harvard Medical School.on finding out which pollutants are most toxic, as
"These new findings, demonstrating that incidencewell as which patients are at greatest risk for
of clot-based strokes also increase, [are] inhealth problems stemming from air pollution.
keeping with our earlier data showing a relationship"Taken together with previous work, these latest
between air pollution and heart and lung disorders,"results support the idea that reducing exposure to
he notes.particulate matter may reduce the risk of strokes
The researchers also looked at the incidence ofand heart attacks," they conclude.