Add another health risk to the use of e-cigarettes: New research shows that vaping instantly stiffens and tightens your blood vessels.
The small study of healthy young adults discovered that even e-cigarettes without nicotine caused a short-lived drop in blood vessel function.
The long-term consequences of that are unclear. But researchers said the findings add to evidence that e-cigarettes are not benign - and not only because they contain nicotine. The liquids used in the devices appear to be harmful, too.
"We know from research conducted to date that 'e-liquids' contain chemical substances and ultra-fine particles that are toxic and carcinogenic to the human body," said Pat Aussem, director of clinical content and development at the nonprofit Center on Addiction.
Aussem, who was not involved in the study, said the findings add to a growing body of evidence on the short-term harms of vaping.
Those risks, she noted, include acute injuries to the lungs, wheezing and asthma exacerbation, and "nicotine toxicity" -- which can cause vomiting, migraines and seizures.
Less is known about long-term health consequences, Aussem said. But, she added, impairments in blood vessel function or lung cells are likely to contribute to heart or lung problems down the road.
And with teenagers and young adults, Aussem noted, the concerns are not only those long-term health issues: Nicotine affects the developing brain in ways that might impair kids' learning and behavior, or "prime" them to be more vulnerable to other substance abuse.
E-cigarettes are battery-powered devices that work by heating a liquid that contains nicotine and other substances, such as propylene glycol and glycerol. The heating creates a "vapor" that is inhaled.
"Often, people think the only bad component is the nicotine," said the study's senior researcher Felix Wehrli.
But the heating and vaporization of the liquid creates a toxic chemical brew, explained Wehrli, a professor at the University of Pennsylvania's Perelman School of Medicine.
Based on government figures, however, many young e-cigarette users are unaware of that.
These days, U.S. teens are more likely to vape than to smoke, according to the U.S. National Institute on Drug Abuse. Among high school seniors, 16% say they used e-cigarettes in the past month, while only 11% smoked.
And of kids who vape, a full two-thirds believe the devices contain "just flavoring." Another 14% say they don't know what they are inhaling.
For the latest study, Wehrli's team had 31 nonsmoking young adults inhale vapor from an e-cigarette that contained the typical e-liquid ingredients, except for nicotine. All had their blood vessel function measured before and after vaping - via MRI scans of the large femoral artery in the leg.
The researchers used a cuff to first constrict the blood vessels of the thigh. Then they released the cuff and measured the femoral artery's dilation in response to the rush of blood.
Overall, the study found, participants' arteries showed a 34% reduction in dilation after vaping. That, in turn, meant less blood and oxygen flowing to the leg.
The effect was seen one to two hours after vaping, according to Wehrli. If someone used e-cigarettes repeatedly over time, he said, that might raise the risk of heart disease.
"This should be a warning to young people to stay away from these products," Wehrli said.
Aussem agreed. "It's important to know that while [vaping] may be safer than smoking conventional cigarettes, there are significant short- and long-term health risks," she said.
The findings were published online Aug. 20 in the journal Radiology.