MONDAY, Dec. 15, 2003 (HealthDayNews) -- Air pollution is a much more dangerous factor for heart attack and other cardiovascular diseases than has been thought, and it is especially dangerous for smokers, a long-term study finds.
"It's not that air pollution doesn't affect the lungs," says study author C. Arden Pope III, an epidemiologist at Brigham Young University. "It clearly does. But it appears that long-term exposure to air pollution expresses itself more in cardiovascular disease than in respiratory disease."
Pope and his colleagues looked at data from the 16-year-long Cancer Prevention Study II, which ran from 1982 and to 1998 and matched death rates and air pollution levels for more than half a million Americans in 156 metropolitan areas.
More than 22 percent of the people taking part in the study died -- 45 percent from cardiovascular diseases, including heart attack, heart failure and cardiac arrest, the researchers report in Dec. 16 issue of Circulation. Respiratory disease accounted for only 8.2 percent of the deaths.
"That was a bit of a surprise," Pope says. "I would have anticipated that we would see more of an effect on respiratory disease."
The analysis centered on levels of one particularly damaging kind of pollution, the fine particles produced by industrial processes, the burning of coal and other fuels, and by automobile engines, especially diesels.
An increase of 10 micrograms per cubic meter of air raised the risk of all cardiovascular diseases and diabetes by 12 percent, the analysis shows. The increased risk for heart attacks and other events caused by blockage of an artery was 18 percent.
Smokers, even those who managed to quit, had it worst. Former smokers had a 26 percent higher risk of dying from cardiovascular disease than people who never smoked. Current smokers had a 94 percent higher risk than people who never smoked.
That, too, was a surprise, Pope says. "My assumption going into this was that in smokers, the additional risk of air pollution would not be high," he says. But the results show that adding air pollution to smoking multiplies the ill effects of both.
The study adds evidence to support the growing belief that inflammation plays an important role in atherosclerosis, the process by which arteries become blocked to cause cardiovascular disease, he says.
"What we hypothesize is that air pollution is one means by which we get inflammation," Pope says. "Chronic exposure to air pollution results in low-grade, chronic inflammation that results in the more rapid progression of atherosclerosis."
An accompanying editorial by Dr. Robert L. Johnson Jr., a professor of medicine at the University of Texas Southwestern Medical Center in Dallas, says the results can be explained by a steady reduction in the number of smokers.
"In the 1950s and 1960s, air pollution primarily affected people with existing lung disease, most of whom were smokers," Johnson says. "Over the past 10 to 15 years, it appears to be affecting the heart more than the lungs. But when you put all the data together, the effect of air pollution on the lungs hasn't changed. The fact that fewer people are smoking means that there are fewer with existing lung disease that can be damaged by air pollution, and so the damage done to the heart becomes more evident."
"This is an important message to people who smoke."
An explanation of how air pollution damages the heart can be found at the American Heart Association. Meanwhile, the American Lung Association can help you quit smoking.