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.
|
