The number of deaths and heart attacks due to second-hand smoke exposure may fall by as much as 30 percent if current downward trends in passive smoking exposure continue, according to a new report.

"Exposure to passive smoking has been reduced by 25 percent to 40 percent, and its burden has been reduced by 25 percent and 30 percent over the last 8-10 years, but the burden remains substantial," Dr. James M. Lightwood and colleagues write in the American Journal of Preventive Medicine.

Lightwood of the University of California San Francisco and his team used the Coronary Heart Disease Policy Model to gauge the health and cost burden of passive smoking on US residents over 35. The model is a computer simulation of the impact of heart disease caused by smoking, blood pressure, cholesterol levels and other factors.

The researchers estimated the prevalence of passive smoking exposure by looking at measurements of cotinine, a nicotine byproduct, in the blood of people participating in the National Health and Nutrition Evaluation Survey. At least a quarter of people 35 to 84 met the strictest criteria for second-hand smoke exposure, while up to 40 percent of men and 30 percent of women are exposed to some level of second-hand smoke.

Based on the assumption that passive smoke exposure boosts heart disease risk by 26 percent to 65 percent, for 1999-2004 Lightwood and his colleagues peg the number of heart disease deaths a year due to passive smoking at 21,800 to 75,100, and estimate that second-hand smoke causes 38,100 to 128,900 heart attacks.

If the downward trend in passive smoking exposure observed between 1988 and 2004 continued through to 2008, according to the researchers, deaths and heart attacks due to second-hand smoke would fall by 25 percent to 30 percent.

Continued reduction in second-hand smoke exposure will likely be driven by efforts to ban smoking in public and in the workplace and to promote smoke-free homes, they conclude.