Boston: The flavouring liquid used in electronic cigarettes may increase the risk of cardiovascular disease when inhaled, a Stanford study warns.
Scientists investigated the effect of the e-liquids on cells called endothelial cells that line the interior of blood vessels.
The study, published in the Journal of the American College of Cardiology, found that endothelial cells exposed to the e-liquids or to blood collected from e-cigarette users shortly after vaping are less viable and exhibit significantly increased levels of molecules implicated in DNA damage and cell death.
The cells are also less able to form new vascular tubes and to migrate and participate in wound healing.
The severity of the damage, aspects of which occur even in the absence of nicotine, varies among popular flavours, the researchers said. Cinnamon and menthol were found to be particularly harmful.
"Until now, we had no data about how these e-liquids affect human endothelial cells," said Joseph Wu, director of the Stanford University in the US.
"This study clearly shows that e-cigarettes are not a safe alternative to traditional cigarettes," Wu said.
"When we exposed the cells to six different flavours 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," he added.
The researchers studied human endothelial cells generated in the laboratory from what are called induced pluripotent stem cells, or iPS cells.
Human iPS cells can become many different cell types, and they provide an ideal way for researchers to closely study cells that would be difficult to isolate directly from a patient.
Endothelial cells line the interior surface of blood vessels and play a critical role in heart and cardiovascular health.