A new medical study showed that flavored e-cigarettes might increase the risk of cardiovascular disease (CVD) such as a heart attack when inhaled. The study also noted that some flavorings are more dangerous to the heart than others.

The study by Stanford University investigated the effect of the e-liquids on the endothelial cells lining the interior of blood vessels. It found that endothelial cells exposed to e-liquids in e-cigarettes exhibited much higher levels of molecules implicated in DNA damage and cell death.

Endothelial cells exposed to e-liquids were also less able to form new vascular tubes and to migrate and participate in wound healing, according to the researchhers who conducted the study.

What was also surprising was the severity of the damage that occurred despite the absence of nicotine. Damage to the endothelial cells varied among popular flavors, but cinnamon and menthol were found to be the most harmful among the six flavors tested by the researchers.

“Until now, we had no data about how these e-liquids affect human endothelial cells,” said Dr. Joseph Wu, M.D., Ph.D., director of the Stanford Cardiovascular Institute and professor of cardiovascular medicine and of radiology.

“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. The cells were less viable in culture, and they began to exhibit multiple symptoms of dysfunction,” Wu added.

The researchers investigated the effect of six popular e-liquid flavorings: cinnamon, fruit, menthol, sweet tobacco with caramel and vanilla, sweet butterscotch and tobacco. These had nicotine levels of 0, 6 and 18 milligrams per milliliter on endothelial cells derived from human iPS cells.

Researchers found several of the e-liquids were moderately toxic to the endothelial cells. But cinnamon- and menthol-flavored e-cigarettes significantly lowered the viability of the cells in culture, even in the absence of nicotine. Exposure to the e-liquids also increased the levels of molecules associated with programmed cell death.

Exposing endothelial cells 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.

Endothelial cells exposed to cinnamon, caramel and vanilla flavors exhibited an increased uptake of low-density lipoproteins and lipids. The process responsible for this is commonly associated with inflammation and endothelial dysfunction. It also limits the ability of endothelial cells to migrate to heal wounds or scratches.

The study showed e-cigarettes with caramel and vanilla flavorings also disrupted cell growth, but not as severely.

CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction orheart attack, stroke, heart failure, congenital heart disease, hypertensive heart disease, rheumatic heart disease, cardiomyopathy, heart arrhythmia, thromboembolic disease, valvular heart disease, aortic aneurysms, peripheral artery disease, carditis and venous thrombosis.

While many forms of e-cigarette advertising increase the odds that teens will try the devices, a new U.S. study suggests that this generation of digital natives is most enticed by promotions they see online. Justin Sullivan/Getty Images