In Brief

Flavor danger

Harmful effects of e-cigarettes are heightened by cinnamon, menthol and other flavorings

Though vaping is thought by some to be safer than smoking cigarettes, new research suggests that the flavorings in the liquid inhaled by users present heart-damaging risks beyond the negative effects of nicotine.

Rain Ungert / EyeEm image

To conduct the study, a Stanford-led team of researchers generated endothelial cells, which line the interior of blood vessels, from stem cells. They then tracked the effects on these lab-grown cells of six popular e-liquid flavors — cinnamon, sweet butterscotch, fruit, menthol, tobacco, and sweet tobacco with caramel and vanilla. They studied the impact of these e-liquids with nicotine levels of 0, 6 and 18 milligrams per milliliter.

While several of the liquids were moderately toxic to the endothelial cells, cinnamon- and menthol-flavored e-liquids significantly decreased the viability of the cells, even in the absence of nicotine.

Further research showed that the e-liquids also increased the production of molecules that can cause DNA damage and cell death. Some also compromised the cells’ ability to form tubes associated with the growth of new blood vessels, and some impaired migration — which enables endothelial cells to heal wounds or scratches.

“Until now, we had no data about how these e-liquids affect human endothelial cells.” 

Some of the effects of exposure to the various e-liquids were dependent on nicotine concentration. Others — like impaired cellular migration and decreases in cell viability — were independent of nicotine, suggesting a combined effect of nicotine concentrations and flavoring components.

“Until now, we had no data about how these e-liquids affect human endothelial cells,” said Stanford cardiologist and stem cell researcher Joseph Wu, MD, PhD, who was senior author of an article about the research in the May 27 Journal of the American College of Cardiology. The lead authors were former postdoctoral scholars Won Hee Lee, PhD, and Sang-Ging Ong, PhD.

“This study clearly shows that e-cigarettes are not a safe alternative to traditional cigarettes,” said Wu, director of the Stanford Cardiovascular Institute.

Krista Conger is a science writer for the medical school's Office of Communication & Public Affairs. Email her at kristac@stanford.edu.

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