SMOKING ISN’T GOOD for you. But e-cigarettes, with their sleek, USB bodies and mango-flavored cartridges, promised a sweeter, safer future. No tar, no combustion, no problem. But that picture is getting more complicated. Last week, the Centers for Disease Control announced that it is opening an investigation into the health effects of smoking e-cigarettes, after nearly 100 teenagers in 14 states reported lung illnesses related to vaping. The cases, which were primarily reported among teenagers and young adults, were so severe that some patients were hospitalized and put on ventilators.

So a study out Tuesday in the journal Radiology comes not a moment too soon. In it, researchers show that inhaling e-cigarette vapor—just the vapor, without any nicotine or flavorings—has an immediate, negative impact on the vascular system.

E-cigarettes first appeared on the market in 2007 and in the years since, vaping among teens has skyrocketed. The CDC estimates that one in five high school students use e-cigarettes. From 2017 to 2018, e-cigarette use among teenagers increased by more than 75 percent, prompting the US Surgeon General to call it an “epidemic.”

Yet not much is known about the harms associated with e-cigarettes. Sure, nicotine is harmful even when it isn’t smoked: vaping nicotine is still highly addictive, can harm the development of adolescent brains, and can even cause seizures. But e-cigarettes contain more than nicotine, and the bulk of research so far has largely overlooked how these other ingredients affect users.

Researchers at the University of Pennsylvania’s Perelman School of Medicine simplified the question. They removed nicotine and flavorings and just looked at what inhaling that basic vapor does to a person’s blood vessels.

Using an MRI, the researchers examined the veins and arteries of 31 people before and after they took a few puffs of an e-cigarette. Their e-cigarettes contained only vape juice, a mixture consisting primarily of water and either glycerol or propylene glycol, which keep everything dissolved inside the cartridge. The test subjects—who were all between the ages of 18 and 35—were nonsmokers and first-time vapers. But after taking 16 three-second puffs, the participants had worse circulation, stiffer arteries, and less oxygen in their blood. “The results of our study defeat the notion that e-cigarette vaping is harmless,” says Felix Wehrli, the study’s principal investigator.

Although glycerol and propylene glycol are considered safe to eat, they may not be safe to inhale. Wehrli’s study shows that when the chemicals are heated and inhaled, they end up passing through the lungs and into the arteries and veins that make up our vascular system. Once there, they irritate the epithelium, a thin layer of cells that lines blood vessels and helps regulate blood flow, blood clotting, and immune responses. The inflamed epithelium then alters how arteries expand and contract. “We did expect an effect, but we never thought the effect was as big as what we found,” notes Wehrli. “It’s not just a little change we detect—it’s a major effect.”

Healthy blood vessels naturally widen and constrict to regulate how much blood is flowing through the body. When Wehrli and his colleagues examined three arteries in the leg, heart, and brain, they found that vaping constricted each one by more than 30 percent. That meant that blood wasn’t flowing as quickly as it was prior to inhaling the vapor. The researchers also found that vaping reduced the amount of oxygen in the blood by 20 percent, and made the walls of the blood vessels more rigid and stiff—a symptom often associated with cardiovascular diseases like hypertension and stroke. Other studies have found similar results in animals, but this is the first such finding in human subjects. “It’s really stunning,” says Sven Jordt, who studies e-cigarettes at Duke University and who was not involved in this study.

An ill-functioning epithelium can have major impacts on your health. Over time, inflammation can cause plaque to collect in blood vessels, a condition known as atherosclerosis that can lead to heart attack or stroke. The effects seen in this study, however, were short-lived. The participants regained their normal vascular function in a couple of hours. One puff won’t cause serious, chronic disease, but pull on a vape a few times every hour—or go through a whole cartridge in a day—and the outcomes could be different.

Like many laboratory tests, the parameters of this study didn’t exactly match the real world. In an emailed statement, Juul, the San Francisco-based e-cigarette company that controls more than 70 percent of the US market, points out that the study “called for a forced puffing regime that is unrealistically high in volume with very limited time between puffs.”

It’s also true that these vascular responses aren’t unique to smoking. Lots of behaviors and environmental factors can trigger blood vessels to constrict, without causing harm. “A host of other activities, including exercise and caffeine use, have been shown to impact vascular activity acutely, but these short-term changes don’t necessarily have any long-term prognostic value,” says Gregory Conley, president of the American Vaping Association, an organization that promotes vaping products.

But while the long-term impact of this research is unknown, it does add to a growing body of evidence on the harms of e-cigarettes. Some studies have shown that vape juice is chemically unstable and that while the cartridges sit on the shelf, reactions in the liquid can create toxic chemicals. Another study shows e-cigarettes cause wheezing, and yet another found that vaping is associated with emphysema and chronic bronchitis.

“Inhaling chemicals into your lungs is dangerous,” says Erika Sward, a spokesperson for the American Lung Association, which does not recommend that anyone use e-cigarettes. For those looking to quit smoking, the ALA recommends using FDA-approved medications, patches, gums, or counseling programs, rather than turning to e-cigarettes. “E-cigarettes are guilty until proven innocent and we are very much in the guilty stage,” says Sward.

The scientific evidence is mounting, but it is not keeping up with the growth of the e-cigarette market. On Monday, a regulatory filing showed that Juul raised another $325 million to expand its business worldwide.


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