Linked to Heart Attacks
Texas, June 12, 2001 (ENS) - As few as two hours after
being inhaled, tiny, invisible air pollutants can penetrate
the lungs' natural defenses and may trigger a heart attack,
says a new report. The study, which appears in today's "Circulation:
Journal of the American Heart Association," warns of particular
problems for people who are already at risk for heart disease.
from diesel buses is a major source of fine particle air
pollution in urban areas
(Photo courtesy EPA)
Previous studies have shown that long term exposure to air
particulates can initiate a chain of events that trigger a
heart attack in individuals with cardiovascular disease or
cardiovascular risk factors.
of hospital admissions and emergency department visits have
linked exposure to particulate air pollution with increased
risk of cardiovascular diseases," said study author Dr.
Murray Mittleman, director of cardiovascular epidemiology
at Boston's Beth Israel Deaconess Medical Center. "But the
current study is the first to examine short term transient
effects of air pollution on the risk of heart attack."
Between January 1995 and May 1996, researchers interviewed
772 Boston area heart attack patients about four days after
their heart attack to establish when their symptoms began.
Participants were enrolled in the Determinants of Myocardial
Infarction Onset Study, which is aimed at gathering information
about factors associated with myocardial infarction, or
Researchers compared the times heart attack symptoms began
with daily air pollution measurements collected in Boston
during the study period. They paid special attention to
levels of the smaller pollutants.
tiny particles are known as PM2.5 because they measure less
than 2.5 micrometers in diameter," explained coauthor Dr.
Douglas Dockery, professor of environmental epidemiology
at the Harvard School of Public Health. "They are so small
that they can get past the normal defense mechanisms in
the lungs and penetrate deeply into the air exchange regions,
like this one in Michigan, emit fine particle air pollution
(Photo courtesy Lake Michigan Federation)
Air pollution measurements taken at the time patients said
their heart attack symptoms began were compared to measurements
taken during control periods. Control periods were selected
24 hours apart, starting three days before the date and time
heart attack symptoms began.
The risk of heart attack was higher in patients who had
been exposed to elevated PM2.5 in the two hours before the
onset of their symptoms. The researchers also found that
a higher heart attack risk was related to a higher average
exposure over the full day before the onset of symptoms,
indicating a delayed response to the particles.
The study concluded that there was a 48 percent higher risk
of heart attack when PM2.5 concentrations increased by 25
micrograms per cubic meter of air in the two hours before
Fine particulate air pollution is produced primarily by
automobile engines, power plants, refineries, smelters and
other industries, Dockery said. Larger, more readily noticed
particles of airborne dust and debris from farming, construction
work and mining are far less likely to trigger heart attack,
sources like this Michigan steel mill are also sources of
(Photo courtesy EPA)
Some recent data suggest that exposure to high levels of
PM2.5 may cause increased systemic inflammation, increased
plasma viscosity (thicker blood) and an increase in certain
proteins in the blood that can cause clots to form.
too early to predict what types of medical intervention
might be effective in preventing the serious cardiovascular
consequences of fine particle exposure," Mittleman adds.
"More research is needed to determine the exact mechanisms
by which inhaling fine particles can set off heart attacks."
Many other major metropolitan areas have higher average
levels of PM2.5 pollution than Boston, the researchers note,
meaning that residents of those cities may face even greater
risk of pollution related heart attacks than Bostonians.
the Boston exposure data can be generalized to other communities,
we would expect proportionately higher effects in more heavily
polluted cities," Dockery said. "But despite the widespread
assumption that particulate air pollutants are primarily
an urban problem, they can also affect large regions located
downwind from the cities. Some of the highest PM2.5 concentrations
are often found far from major urban areas, in places where
we would expect the air to be cleaner."
Mittleman said one bit of encouraging news is that levels
of the tiny pollutants have decreased somewhat in most urban
areas over the past few years.
Clean Air Act has brought about substantial reductions in
air pollution since this photo of Los Angeles was taken
in 1972 (Photo by Gene Daniels, courtesy EPA)
particle pollution is largely a summer phenomenon, Dockery
monitors show seasonal variations where hot, hazy days have
higher levels of fine particles on average," he said. Also,
Dockery said it is much more difficult for individuals to
take protective measures against PM2.5 than against gaseous
pollutants like carbon monoxide, which can be removed from
of their size, these particles readily penetrate indoor
spaces," noted Dockery, "but air conditioning helps somewhat,
reducing indoor concentrations by 30 percent to 50 percent.
The best advice is to avoid outdoor activity on hot, hazy
days. If a person exercises outside, the increased respiratory
activity also increases the dose of PM2.5."
urban areas have trouble meeting clean airstandards, in
part due to exhaust from trucks and buses (Photo
The U.S. Environmental Protection Agency's (EPA) current
acceptable standard is 65 micrograms of PM2.5 per cubic
meter of air.
at PM2.5 concentrations below that standard, our study shows
that the risk of a heart attack is increased," said Mittleman.
"Our findings suggest that people who have heart disease
or an elevated risk of heart attack would be well served
to avoid being outdoors for extensive periods of time when
the air quality is poor. This is especially the case on
the hot, hazy days of summer when the problem is much more
Mittleman said that more research is needed to determine
how a person's exposure to high levels of fine particulate
air pollution can lead to a heart attack. Understanding
that triggering mechanism, he believes, could spur the development
of new drugs that could protect individuals during peak
exposure to air pollution, such as they would experience
during rush hour traffic or outside on a hot summer day.