Vaping may create dangerous toxins that temporarily reduce blood flow and damage blood vessels, according to a new study. What's more, these effects were seen when people used e-cigarettes that did not contain nicotine.

While the dangers of smoking cigarettes are very well established, the health effects of smoking electronic cigarettes aren’t clear. Recently, the Centers for Disease Control and Prevention announced an investigation into a string of mysterious vaping-related illnesses that have landed nearly 100 people in the hospital.

But knowing that the effects of vaping may spread further than the lungs, the researchers wanted to investigate the effects of e-cigarettes on the body's blood vessels and blood circulation.

To do this, they recruited 31 healthy adults who did not smoke; researchers tied a tight cuff around one thigh of each participant. They kept this cuff on for a couple minutes, restricting blood flow through a major vein and artery in the leg, known as the femoral artery and vein.

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Then, the researchers took the cuff off and used magnetic resonance imaging (MRI) to measure participants' blood flow. Typically, when blood is restricted in this way, there will be a demand for increased blood flow when the cuff is removed, because the tissue is starved of oxygen and nutrients, said senior author Felix Wehrli, a professor of radiologic science and biophysics at the University of Pennsylvania Perelman School of Medicine.

Indeed, the researchers saw that when they removed the cuff, participants' blood flowed much faster, reaching a peak velocity before dropping back down to normal levels after a minute or so. Next, the participants took 16 puffs of an e-cigarette that did not contain nicotine and once again had a cuff tied to their legs and their blood vessels imaged.

Post-vaping, the participants' blood vessels did not dilate, or widen, as much as before to let blood through. In fact, after a participant smoked, the vessels dilated, on average, 34% less than they did before vaping. What's more, blood acceleration was 25.8% slower, peak blood flow — the maximum blood flow through the vessels— was reduced by 17.5%, and oxygen levels in the vessels dropped by 20%.

The findings suggest that vaping, even just once, leads to temporary changes that impair blood vessel function, the authors said.

"This normal [blood circulation] response is blunted by e-cigarette exposure," and the reason is likely because of the ingredients found in e-cigarettes, Wehrli told Live Science. E-cigarettes come in a wide variety of brands and flavorings and so they may have a giant list of ingredients. But the basic ingredients, propylene glycol and glycerol, are pretty much the same, he added.

When propylene glycol and glycerol are heated to high temperatures, they form other substances that are known to be toxic, he said. In a previous paper, the same team showed that smoking e-cigarettes actually caused a "toxic immune response" in the endothelium, or blood vessel lining.

However, these studies looked only at the very short-term effects of vaping, and participants' blood vessels returned to normal within an hour or so, Wehrli said. So the "effect we see is transient," he said.

Extrapolating a bit, "one could argue" that if someone keeps on vaping all day, every day over years, the body doesn't have time to revert to baseline — and vaping might lead to disease, Wehrli said. But future studies that follow people for many years will be needed to prove this, he added.

"This well-done paper adds to the evidence that e-cigarettes have immediate deleterious effects on blood vessels," said Stanton Glantz, a professor of medicine at the University of California, San Francisco's Center for Tobacco Control Research and Education, who was not a part of the study. "These changes are both bad in the short run but are also indicators of long-term risk for cardiovascular disease."

Dr. Michael Siegel, a professor of community health sciences at Boston University's School of Public Health, who was also not a part of the study, agrees that this study confirms that e-cigarettes, even without nicotine, cause dysfunction in the blood vessels.

But because this effect is short-lived and completely reversible, "it should not be assumed from this research that vaping is a cause of heart disease or permanent blood vessel damage," he said. "Further research will be needed to determine whether vaping poses a risk of irreversible blood vessel injury."

The study was published today (Aug. 20) in the journal Radiology .