E-cigs may be as harmful to the heart as smoking cigarettes that contain tobacco, a new study suggests.

Coronary heart disease affects more than 15 million Americans and kills 500,000 people a year, making it this nation’s leading cause of death. It is caused by atherosclerosis, the biological process that causes a buildup of fatty substances that narrows the vessels, setting the stage for heart attack, stroke, and other cardiovascular ailments.

The use of e-cigarettes is growing, fueled partly by the belief they are safer than the nicotine found in cigarettes, but a new study indicates that, like cigarettes, they may also escalate this disease process, researchers at the University of Louisville say.

They exposed one set of mice to varying levels of e-cigarette aerosol, tobacco smoke, smokeless tobacco or to an aldehyde produced by tobacco, acrolein, which is thought to pose 80-85 percent of the non-cancer health risk of tobacco smoke. Another set of mice was exposed to nicotine alone to understand whether nicotine by itself had any effect.

Consistent with previous studies, exposure to tobacco smoke increased the amount of atherosclerosis in mice.  But the researchers also found that either e-cigarette aerosol or smokeless tobacco exposure alone also increased this disease process.

The study indicates that multiple tobacco-derived constituents have cardiovascular disease-causing potential, including those that e-cigarettes contain,  say the researchers, who presented their study today at the American Association for the Advancement of Science Annual Meeting in Washington, D.C.