WASHINGTON, May 27 (Xinhua) -- Scientists from Stanford University found that the acute exposure to flavoring liquids for electronic cigarettes may increase the risks of heart disease as it causes cell dysfunction.

The study published on Monday in the Journal of the American College of Cardiology showed that when lab-grown endothelial cells that line the interior of blood vessels were exposed to the e-liquids, they exhibited significantly increased levels of molecules implicated in DNA damage and cell death.

Those cells are also less capable of forming new vascular tubes and participating in wound healing, according to the study.

They found that at least six popular flavors with or without nicotine had toxic effect and the cinnamon and menthol flavors were particularly harmful.

"This study clearly shows that e-cigarettes are not a safe alternative to traditional cigarettes. When we exposed the cells to six different flavors of e-liquid with varying levels of nicotine, we saw significant damage," said Joseph Wu, professor of cardiovascular medicine and of radiology at Stanford, in a statement.

The researchers investigated human endothelial cells generated in the lab from induced pluripotent stem cells or iPS cells, which was the first of its kind study. Human iPS cells can become many different cell types, providing a way to study cells that would be difficult to isolate directly from a patient.

In the United States, cardiovascular disease is responsible for about one-third of smoking-associated deaths in smokers. E-cigarettes may decrease the risk of cancer, but its effect on vascular health has been unclear.

In the new study, the researchers found exposure to the e-liquids increased the relative levels of molecules that can cause DNA damage, which are associated with programmed cell death.

Also, the exposure to the cinnamon and menthol flavored e-liquids significantly disrupted the ability of the cultured cells to form capillary-like tubular structures associated with the growth of new blood vessels, according to the study.

They found that some of the effects of exposure to the various e-liquids were dependent on the nicotine concentration, but others, like cellular migration and decreases in cell viability, were independent of nicotine.

The researchers warned that e-cigarettes can be deceptive since when people are smoking a traditional cigarette, they have a sense of how many cigarettes they are smoking, but e-cigarette smokers are much easier to expose high level of e-liquids over a short time period.