UW study shows pollution linked to heart attacks
It looks at diesel, other particulates in the air
By TOM PAULSON
P-I REPORTER
A nationwide research project coordinated out of Seattle has provided
further evidence that exposure to air pollution raises the risk of
heart attacks, heart disease and stroke.
"We've found this risk to be even stronger than previously
recognized," said Dr. Joel Kaufman, a University of Washington expert
on environmental health who led the study published in today's New
England Journal of Medicine.
The results, though derived from a large research project involving
only older women, almost certainly apply to men as well, Kaufman
said.
The study was focused on exposure to a common but invisible, fine
particulate form of air pollution produced by diesel exhaust, coal-
fired power plants and many other sources. The UW scientists looked at
36 cities with wide variation in the levels of these air pollutants.
Many cities routinely test for air concentrations of these particles,
known as PM2.5s. This refers to their size, which is less than 2.5
microns -- or less than one-tenth of the diameter of a human hair.
Many scientists believe it is, in part, the small size of these
particles that make them so toxic.
"Seattle was included, and we're about in the middle range in terms of
levels," Kaufman said. The lowest average level measured by the study
was in Honolulu, at 3.4 micrograms (one millionth of a gram) per cubic
meter. The highest was Riverside, Calif., at 28 micrograms. Seattle
had PM2.5 air levels of 11 micrograms.
"That's not terrible, but it's still in the higher range in terms of
risk," Kaufman said. Levels of exposure to fine particulates vary
within a city, he noted, which the researchers also considered when
looking at an individual's health outcomes.
"Our findings show that both what city a woman lived in, and where she
lived in that city, affected her exposure and her disease risk," said
Kristin Miller, a UW doctoral student in epidemiology and first author
of the journal report.
The UW scientists found that an increase of 10 points in the PM2.5
levels increased a woman's risk of a heart attack or other
"cardiovascular event" by 24 percent and risk of death from heart
disease by 76 percent.
The link between air pollution and disease, especially cardiovascular
disease, has been shown in numerous earlier studies, Kaufman noted.
But most of the earlier research was retrospective, he said, based on
reviewing death certificates and estimating the deceased's past
exposure to pollution.
"Because these findings have direct impact on clean-air regulations,
they are often fiercely challenged by critics in industry," Kaufman
said.
"Preventing these effects requires reducing the pollution at the
source."
The implications of this connection could be very significant.
"More than one out of three deaths in the United States are due to
cardiovascular disease -- it's the leading cause of death," Miller
said. "If the annual average concentration of fine particulate air
pollution can be reduced, it would potentially translate on a national
scale to the prevention or delay of thousands and thousands of heart
attacks, strokes and bypass surgeries, not to mention fewer early
deaths."
An editorial from researchers at the Harvard School of Public Health
and Brigham and Women's Hospital accompanies the UW study. The authors
suggest public-health interventions to address this problem and
upgrading the federal standards to reduce fine particulate matter
pollution.
The Environmental Protection Agency tightened its daily limit for fine
particulate pollutants in September. But it left the average annual
limit untouched, allowing a concentration of fifteen-millionths of a
gram for every cubic meter of air.
The strength of the UW findings, researchers say, comes from more
accurate air-pollution measurements in recent years and a massive
treasure trove of biomedical data available through a multipurpose
research project, involving more than 65,000 women, known as the
Women's Health Initiative Observational Study.
The Women's Health Initiative, funded by the National Institutes of
Health and administered by the Fred Hutchinson Cancer Research Center,
was started in 1991 to look at the health effects of hormone therapy
in post-menopausal women. Because of its extraordinarily large number
of participants and statistical power, it has since been used to try
to answer many other, broader questions of health and disease.
Although the data is now fairly convincing showing the link between
fine particulate air pollution and heart disease, the UW scientist
said it remains unclear exactly how these tiny particles in such small
doses are able to so vigorously attack the heart.
"Do these particles get into the (blood) circulation, or do they have
an effect in the lungs that propagates downstream?" Kaufman said. "We
really don't know, and we need to figure this out."
Another unknown is which type of PM2.5 particles are the worst, he
said. Studies done in cities with varying levels of air pollution have
shown an increase of heart attacks correlating with increases in
diesel exhaust, Kaufman said. But a study of wood smoke in Seattle
showed no such correlation between high levels of wood smoke and heart
attacks, he said.
"We've seen that the arteries constrict after exposure to diesel
exhaust," Kaufman said. "I think it's a particularly bad actor, but we
don't have the smoking gun yet."
Evidence of the link between heart problems and pollution dates back
at least to a 1952 disaster in London known as the "Great Smog." A
cold December fog trapped coal smoke in an inversion, killing
thousands of people (8,000, by one estimate) and prompting new clean-
air regulations.
LEARN MORE
To determine the average annual concentration of fine particulate
matter for a particular city or county, visit the EPA's Air Trends Web
site and look for "PM 2.5 Wtd AM" in the tables provided. The most
recent data available from the EPA are from 2005. epa.gov/airtrends/
factbook.html
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