(DrAbbate, iStockphoto)

New research shows that electronic cigarette use may harm cardiovascular health, adding to the growing list of concerns about their safety.

The study, which will be presented next Monday at the American Heart Association's Scientific Sessions meeting in Chicago, investigated the effect that e-cigarettes have on the endothelial cells that line the inside of the body's blood vessels. Endothelial cells produce nitric oxide, a molecule that helps keep blood vessels healthy and control blood pressure levels.

Chemicals in traditional cigarettes decrease the production of nitric oxide, which is one of the reasons smoking causes heart damage. The new study was designed to see if e-cigarettes have a similar effect.

The researchers collected blood samples from 36 tobacco users, e-cigarette users and nonsmokers. In the lab, they exposed blood vessel endothelial cells to the volunteers' blood serum. The serum is the liquid that remains after the red and white blood cells, blood platelets and clotting factors have been removed.

The lab results showed that endothelial cells exposed to blood serum from e-cigarette users produced less nitric oxide and contained less of the enzyme that produces nitric oxide compared to serum from nonsmokers.

"We showed that blood serum from electronic cigarette users has harmful effects that are similar to that of (tobacco) cigarettes on endothelial cell functions," said the study's lead researcher, Dr. Leila Mohammadi, a postdoctoral fellow at the Cardiovascular Research Institute at the University of California, San Francisco. "This harmful effect is likely to adversely affect arteries and cardiovascular health."

Matthew Springer, the study's principal investigator, said the findings highlight another safety concern related to e-cigarettes.

"You have various products (like e-cigarettes) that are assumed to be safer than cigarettes, and they might be, but safer isn't the same thing as harmless," said Springer, a professor of medicine at the University of California, San Francisco.

Aruni Bhatnagar, a professor of medicine at the University of Louisville and co-director of the AHA's Tobacco Regulation and Addiction Center, called the study "a step in the right direction."

"There is a push from the tobacco industry to say e-cigarettes are safer," said Bhatnagar, who was not involved with the research. "But this study raises a flag and supports the idea that e-cigarettes are not harmless to cardiovascular health. There is significant (blood vessel) injury that might be associated with long-term e-cigarette use."

It is not known what substance contained in e-cigarettes caused the decrease in nitric oxide, the researchers noted.

Mohammadi and Springer both said they'd like to see future studies that look at the health of actual endothelial cells in the blood vessels of e-cigarette users. They would also like to see studies that look at the effects of the specific ingredients and flavors in e-cigarettes, including nicotine, propylene glycol and glycerin.

"All of the different flavors are a different chemical, and some of them could have harmful effects," Springer said.

One big challenge facing researchers is the constant introduction of new e-cigarette products, each with its own list of ingredients, that are marketed as smart alternatives to smoking.

The research is showing "that anything you inhale other than clean air seems to be causing vascular problems," said Springer. "Rather than try to find the things to inhale that aren't as bad as cigarettes, we might have to realize (we need) to just breathe clean air."

Find more news from Scientific Sessions.

If you have questions or comments about this story, please email editor@heart.org.