Liquid used in e-cigarettes damages cells crucial for a healthy heart

The flavors used in e-cigarettes—especially menthol and cinnamon—damage blood vessel cells and such impacts increase heart disease risk, according to a new study.

The study, published today in the Journal of the American College of Cardiology, is the latest to link e-cigarettes, or vaping — which has been touted as a safer alternative to smoking cigarettes—to heart problems. It adds to evidence that e-liquids affect the endothelial cells that line the interior of blood vessels. These cells are crucial in delivering the blood supply to the bodies' tissues and sending cells to promote healthy blood vessels, tissue growth and repair.

E-cigarettes are small devices that heat up liquids (usually propylene glycol or glycerol) to deliver as aerosol mixture of nicotine and flavors.

The study comes as e-cigarette use continues to rise. Roughly 1 in 20 U.S. adults now use e-cigarettes but the real growth is happening among youth: use among U.S. high school students went from 11.7 percent in 2017 to 20.8 percent in 2018, according to the U.S. Food and Drug Administration. In addition, about 4.9 percent of middle school students use e-cigarettes, the FDA found.

Researchers exposed endothelial cells grown in a laboratory to six different kinds of e-liquids and also examined blood collected from e-cigarette users after they vaped. They found the cells, when exposed to the e-liquids, had a sharp increase in the types of molecules linked to DNA damage and cell death.

The cinnamon and menthol flavors also hampered the ability of cells to promote the growth of new blood vessels.

Such changes leave people more susceptible to heart diseases.

"Until now, we had no data about how these e-liquids affect human endothelial cells," Dr. Joseph Wu, senior author of the paper, and a researcher and director of the Stanford Cardiovascular Institute and professor of cardiovascular medicine and of radiology, said in a statement. "This study clearly shows that e-cigarettes are not a safe alternative to traditional cigarettes. The cells were less viable in culture, and they began to exhibit multiple symptoms of dysfunction."

Wu and colleagues looked at various e-liquid flavors — including fruit flavors, caramel, vanilla, butterscotch, sweet tobacco, menthol and cinnamon. Some contained nicotine, some did not.

The cinnamon and menthol flavors were the most toxic to cells, even when there wasn't nicotine in the mixture. "Our findings are concordant with the results of recent studies showing that cinnamon-flavored e-liquids and aerosols are highly volatile, cytotoxic, and genotoxic to human embryonic cells and adult lung cells," the authors wrote.

Beyond the flavors' health impacts, the researchers also found the amounts of nicotine in the blood of both e-cigarette users and traditional smokers were the same after 10 minutes of smoking.

"When you're smoking a traditional cigarette, you have a sense of how many cigarettes you're smoking," Wu said. "But e-cigarettes can be deceptive. It's much easier to expose yourself to a much higher level of nicotine over a shorter time period. And now we know that e-cigarettes are likely to have other significantly toxic effects on vascular function as well."

The study was limited in that the e-liquids weren't heated, which could alter how the exposed cells react. The research, however, is just the latest linking e-cigarettes to heart impacts.

In March, researchers presented a study of nearly 100,000 Americans that found e-cigarette users are more likely to suffer heart attacks and strokes compared to non-users.

Another large national study in January of 400,000 Americans reported e-cigarette users have a 70 percent higher risk of stroke and a 60 percent higher risk of heart attack, when compared to non-users.

With use rising, health groups continue to push for more strict regulation. A judge this month ordered the FDA to review all U.S. e-cigarette products.

The ruling was a response to a federal lawsuit filed by health groups, including the American Academy of Pediatrics and the Campaign for Tobacco-Free Kids, that alleged the FDA hasn't adequately regulated e-cigarettes and is leaving a generation of U.S kids on the path to nicotine addiction.

Editor's note: The story has been updated to reflect that there have been previous studies on endothelial cells and e-cigarette flavor liquids.