The researchers found that on days with high air pollution, current smokers had a greater risk of heart attack than non-smokers.
"Smokers are more sensitive to air pollution, as far as their risk for heart attacks," said study author Yves Cottin, M.D., Ph.D., of the cardiology department at the University of Dijon in Burgundy, France. "When fine particles of less than 10 micrometers (μm), which are mainly attributable to diesel exhaust, exceeded 25 micrograms (μg) per cubic meter, hospital admissions for heart attack rose by 91 percent in the general population and even more in current smokers."
The same may be true for other urban settings around the world, but the data needs confirmation in different geographic areas, Cottin said.
"This is yet another strong case against smoking, and a warning for high-risk people to stay indoors, or refrain from strenuous activities during peak air pollution periods. Doctors could even consider increasing heart disease treatment during those high-risk pollution times," Cottin said.
Studies have shown an association between elevated daily concentrations of environmental air pollution and higher hospital admissions for heart disease. But few studies have looked specifically at exposure to air pollution and the risk of a heart attack.
"Moreover, most of the existing studies did not separately analyze different subgroups, such as smokers versus nonsmokers," Cottin said.
Cottin and colleagues looked at data collected from January 2001 to December 2002 of 322 patients hospitalized for heart attack from the greater Dijon area. Forty-two percent were smokers.
The researchers compared the daily incidence of heart attack with the average daily concentrations in the air of particles smaller than 10μm (PM10). They also measured average levels of ozone, sulfur dioxide, nitrogen dioxide and carbon monoxide.
Researchers included the ATMO index, widely used in France as a daily overall indicator of air quality. The index ranges from one to 10, where one indicates very good and 10 very poor. It is calculated via the daily monitoring of four pollutants, both gases and particles (nitrogen dioxide, sulfur dioxide, ozone and PM10).
Air pollution levels in Dijon remained under four on the ATMO index 86 percent of the time. While the pollution level rose to six or higher only about 5 percent of the time, or about 18 days a year, heart attacks were 161 percent more likely to occur in the general population and 250 percent more likely in smokers during those high-pollution days.
When considered separately, ozone, sulfur dioxide and nitrogen dioxide did not cause measurable detrimental effects, Cottin said. However, the researchers found that particulate matter increased the risk of heart attack, even at levels lower than current national standards.
Studies are under way to follow up with the patients who had heart attacks during the study period to analyze any differences that might exist between heart attacks people have during peak air pollution times versus cleaner air days.
Co-authors are Clotilde Royer, Marianne Zeller, Jean-Pierre Besancenot, Jean-Claude Beer, Mohamed Jolak, Gilles Dentan, Luc Janin-Manificat and Jean-Eric Wolf.