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Air pollution has long been known to
trigger asthma, irritate the eyes, and sting the lungs, but
researchers have discovered an added health threat: It also
causes heart attacks.
Research published today in Circulation:
Journal of the American Heart Association, says a clear link
exists between breathing the tiny, invisible components of
air pollution known as particulates and the onset of heart
attacks.
"Studies of hospital admissions
and emergency department visits have linked exposure to particulate
air pollution with increased risk of cardiovascular diseases,"
said Murray Mittleman, one of the study's authors and director
of cardiovascular epidemiology at Boston's Beth Israel Deaconess
Medical Centre.
The study, the first to examine the
direct, short-term effects of air pollution, found elevated
pollution levels were associated with a nearly 50 per cent
greater risk of heart attacks.
The study was based on interviews of
772 Boston-area heart patients in 1995 and 1996. Four days
after their attacks, they were asked when their symptoms had
begun.
Researchers then compared the onset
of the symptoms with daily air pollution measures.
They found that as little as two hours
after being inhaled, the particles in air pollution can penetrate
the lungs and trigger heart problems.
Environmentalists and public health
officials had strong reactions to the study.
John Wellner, an air-quality specialist
for Pollution Probe, a Toronto group, said the addition of
heart problems to the list of air pollution's effects indicates
that more needs to be done to improve air quality.
Trevor Hancock, environmental spokesperson
for the Heart and Stroke Foundation, said people should try
to minimize their exposure to outdoor air on smoggy days.
"People should take sensible precautions on days when
the weather forecast predicts smog," he said.
The exact mechanism by which air pollution
causes heart attacks isn't yet known, Dr. Mittleman said.
"It's too early to predict what types of medical intervention
might be effective in preventing the serious cardiovascular
consequences of fine particle exposure."
However, some recent data suggest that
exposure to the small particulates in pollution may increase
inflammations, make blood thicker and increase blood proteins
that can cause clots to form.
Although dirty air contains a stew
of harmful chemicals, researchers found heart attacks tracked
the concentration of extremely small particles called PM 2.5.
These particles measure less than 2.5 micrometres in diameter,
meaning it would take dozens to cover even the width of a
human hair.
The particles can be solids or liquid
droplets, and are produced mainly by automobile engines, power
plants, refineries, smelters and other industries.
The particles, often composed of sulphates
and nitrates, are so tiny they become imbedded deep in lung
tissue.
"They are so small that they can
get past the normal defence mechanisms in the lungs and penetrate
deeply into the air exchange regions," said Douglas Dockery,
professor of environmental epidemiology at the Harvard School
of Public Health and another co-author of the study.
The researchers also observed a higher
heart attack risk when 24-hour average exposure to these particles
was considered, indicating that there was also a delayed response
to the pollution.
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