By Cat Lazaroff
DALLAS, Texas, June 12, 2001 (ENS) - As few as two hours after
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.
Smoke from diesel buses is a major source of fine
particle air pollution in urban areas (Photo courtesy
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
"Studies 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 heart attack.
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.
"These 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, or alveoli."
Incinerators, like this one in
Michigan, emit fine particle air
pollution (Photo courtesy Lake
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
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 symptoms began.
Fine particulate air pollution is produced primarily by automobile
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, he added.
Stationary sources like this
Michigan steel mill are also sources
of particulate pollution (Photo
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.
"It's 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
pollution than Boston, the researchers note, meaning that residents of those cities
may face even greater risk of pollution related heart attacks than Bostonians.
"If 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.
The 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)
Fine particle pollution is largely a
summer phenomenon, Dockery
"Pollution 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 indoor air.
"Because 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."
Many urban areas have trouble meeting clean air
standards, in part due to exhaust from trucks and
buses (Photo courtesy EPA)
The U.S. Environmental Protection Agency's (EPA)
current acceptable standard is 65 micrograms of
PM2.5 per cubic meter of air.
"Even 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 prominent."
Mittleman said that more research is needed to determine how
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.
© Environment News Service (ENS) 2001. All Rights Reserved.
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