The Grapevine

E-Cigarette Flavors Can Damage Blood Vessels, Even Without Tobacco

The debate over electronic cigarettes has dominated headlines, from people who celebrate them as smoking cessation tools to those who are concerned about their harmful effects being downplayed.

In a new study, researchers at Boston University School of Medicine (BUSM) focused specifically on how chemical flavorings used in e-cigarettes affect the body. The findings were published in the journal Arteriosclerosis, Thrombosis, and Vascular Biology on June 14.

The team examined nine popular e-cigarette flavorings: Menthol (mint), acetylpyridine (burnt flavor), vanillin (vanilla), cinnamaldehyde (cinnamon), eugenol (clove), diacetyl (butter), dimethylpyrazine (strawberry), isoamyl acetate (banana) and eucalyptol (spicy cooling).

Endothelial cells (the cells lining blood vessels inside the heart) were isolated from smokers and non-smokers. When exposed to the flavoring additives, the cells from non-smokers increased inflammation and decreased the release of chemicals to promote blood flow. Both these effects were said to be indicators of short-term toxicity, which were also observed in the cells of the smokers.

"Our findings show that flavoring additives themselves were directly toxic to blood vessels and have adverse effects that may have relevance to cardiovascular toxicity long-term similar to combustible cigarettes," said lead author Jessica L. Fetterman, an assistant professor of medicine at BUSM.

While previous studies have explored how e-cigarettes may affect blood vessels, the impact of flavoring additives alone has been relatively unclear. All the nine flavors reduced the production of nitric oxide, a molecule which is important for widening vessels in response to greater blood flow.

"Increased inflammation and a loss of nitric oxide are some of the first changes to occur leading up to cardiovascular disease and events like heart attacks and stroke, so they are considered early predictors of heart disease," Fetterman added.

When tested at highest levels, all nine chemicals led to cell death. At lower levels, cinnamon, clove, strawberry, banana and spicy cooling had a similar effect. Strawberry remained harmful even at extremely low levels, suggesting that the cells are particularly sensitive to this flavor.

Three flavorings were heated, to replicate how they are used in e-cigarettes. Nitric oxide decreased again with vanilla and clove, but not with the mint flavor. The study was limited as not all flavors were heated and the tests were conducted outside the human body. 

"Our work and prior research have provided evidence that flavorings induce toxicity in the lung and cardiovascular systems. Flavorings are also a driver of youth tobacco use and sustained tobacco use among smokers," Fetterman said.

In a recent statement by the Forum of International Respiratory Societies, doctors and scientists from around the world urged a ban on flavors as they increased the appeal of e-cigarettes among adolescents and could potentially act as a "one-way bridge" to cigarette smoking.

However, it is unlikely that the debate may end any time soon. Since e-cigarettes were only introduced in the early 2000s, the lack of long-term data means that it is too early to clearly understand their health effects. The American Heart Association advised caution, stating that e-cigarettes should only be used as a last resort to quit smoking.