Medical researchers know that people exposed to high levels of air pollution can have increased risk for asthma and other respiratory problems. But they're slowly finding that people living in areas with lots of air pollution also end up with problems of the heart and cardiovascular system. Now data from a large U.S. study of women confirms a strong relationship between air pollution and an increased risk of dying from cardiac disease and stroke.

Doctor Joel Kaufman, an epidemiologist from the University of Washington in Seattle, looked at data collected from over 65,000 women living in cities across the United States. The researchers linked the health data with pollution measured near the women's homes, specifically microscopic particles of soot and dust.

Kaufman says these particles are found almost everywhere. "It happens anywhere really in an urban area where you have a lot of vehicular traffic, truck traffic, you begin to get a buildup of these fine particles, it also happens in regions of the country where there are coal powered electric plants. Any kind of fossil fuel combustion emits this kind of soot into the air."

The locations Kaufman examined had average levels of these particulate ranging from 4 to 25 micrograms per cubic meter. He found that women who lived in areas with higher levels of air pollution had a greater risk of developing cardiovascular disease. "In fact for every 10 micrograms per cubic meter increase in fine particulate matter, there was a 76 percent increase in the risk of death from cardiovascular disease after you adjust for all the other things, like blood pressure, cholesterol, smoking, diabetes, educational attainment and so forth."

Kaufman says they expected to find increased risk, but the magnitude of the findings surprised them, since it was substantially higher than they had thought it would be. "And we did a lot of work to make the effect go away," he admits. "We did lots of additional analysis to see if there was some quirk in the data or something that was making some falsely elevated hazard estimates occur and, no matter what we did, the effect really persisted and we think that these are the right results."

Kaufman says the results suggest that public policy measures to improve air quality could have substantial implications for human health. He says that reducing air pollution could also have the effect of reducing deaths from cardiovascular disease. The research appears in the New England Journal of Medicine.