A single dose of e-cigarettes may be harmful to the body's blood vessels -- even when the vapour is entirely nicotine-free, a study claims. Smoking e-cigarettes, also called vaping, has been marketed as a safe alternative to tobacco cigarettes and is rising in popularity among non-smoking adolescents, researchers said.
To study the short-term impacts of vaping, the researchers at the University of Pennsylvania in the US performed magnetic resonance imaging (MRI) exams on 31 healthy, non-smoking adults before and after vaping a nicotine-free e-cigarette.
Comparing the pre- and post-MRI data, the single episode of vaping resulted in reduced blood flow and impaired endothelial function in the large (femoral) artery that supplies blood to the thigh and leg, according to the study published in the journal Radiology.
The endothelium, which lines the inside surface of blood vessels, is essential to proper blood circulation.
Once the endothelium is damaged, arteries thicken and blood flow to the heart and the brain can be cut off, resulting in heart attack or stroke.
"While e-cigarette liquid may be relatively harmless, the vaporisation process can transform the molecules -- primarily propylene glycol and glycerol -- into toxic substances," said Felix W Wehrli, a professor at the University of Pennsylvania.
"Beyond the harmful effects of nicotine, we've shown that vaping has a sudden, immediate effect on the body's vascular function, and could potentially lead to long-term harmful consequences," said Wehrli.
E-cigarettes are battery-operated devices that convert liquid into aerosol, which is inhaled into the user's lungs.
Typically, the liquid contains addictive nicotine, as well as flavours.
More than 10 million adults in the US use e-cigarettes, and vaping has become especially popular among teenagers, researchers said.
They examined the impact of an e-cigarette that contained propylene glycol and glycerol with tobacco flavouring, but no nicotine, which study participants took 16, three-second puffs from.
To evaluate vascular reactivity, the group constricted the vessels of the thigh with a cuff and then measured how quickly the blood flowed after its release.
Using a multi-parametric MRI procedure, researchers scanned the femoral artery and vein in the leg before and after each vaping episode to see how vascular function changed.
They then performed a statistical analysis to determine group differences in vascular function before and after vaping.
The team observed, on average, a 34 per cent reduction in the femoral artery's dilation.
E-cigarettes exposure also led to a 17.5 per cent reduction in peak blood flow, a 20 per cent reduction in venous oxygen, and a 25.8 per cent reduction in blood acceleration after the cuff release -- the speed at which the blood returned to the normal flow after being constricted.
These findings suggest that vaping can cause significant changes to the inner lining of blood vessels, said study lead author Alessandra Caporale, a post-doctoral researcher at University of Pennsylvania.
"E-cigarettes are advertised as not harmful, and many e-cigarette users are convinced that they are just inhaling water vapour," Caporale said.
"But the solvents, flavourings and additives in the liquid base, after vapourisation, expose users to multiple insults to the respiratory tract and blood vessels," he said.
Wehrli noted that they observed these striking changes after the participants (all of whom never smoked previously) used an e-cigarette a single time.
More research is needed to address the potential long-term adverse effects of vaping on vascular health, but he predicts that e-cigarettes are potentially much more hazardous than previously assumed. Earlier this year, his research group found that acute exposure to e-cigarettes causes vascular inflammation.
"I would warn young people to not even get started using e-cigarettes. The common belief is that the nicotine is what is toxic, but we have found that dangers exist, independent of nicotine," Wehrli said.
"Clearly if there is an effect after a single use of an e-cigarette, then you can imagine what kind of permanent damage could be caused after vaping regularly over years," he said.