Researchers tested lung fluid from 41 people - nonsmokers, smokers and people who vape -- and found that the lungs of both smokers and vapers had elevated levels of protease enzymes, a precursor condition to emphysema in smokers.
The nicotine in vaping liquids is responsible for the increase in protease enzymes, said the team from the University of North Carolina (UNC) School of Medicine, in Chapel Hill.
The bottom line is that "vaping may not be safer than cigarette smoking," study senior author Robert Tarran said in a UNC news release. He's a professor of cell biology and physiology, and member of the university's Marsico Lung Institute.
As Tarran's team explained, chronic over-activity of protease enzymes in lung cells damages tiny sensitive air sac structures in the lungs.
In smokers, this damage is thought to be the cause of emphysema, an often fatal form of chronic obstructive pulmonary disease (COPD) that results in progressive shortness of breath. There is no cure.
The new findings gave pause to one lung care specialist.
"I have seen many patients using e-cigarettes as a mechanism to stop smoking cigarettes," noted Dr. Thomas Kilkenny, who wasn't involved in the new research.
"Unfortunately, this study calls into question the safety of vaping as a tool to stop smoking. It also demonstrates that a whole generation of young people may be setting themselves up to develop emphysema," he added.
That's because the popularity of vaping is surging among American teens, even as traditional smoking rates decline. In 2018, more than 3.6 million middle and high school students were current e-cigarette users, according to the U.S. Food and Drug Administration. That was up by 78% from just the prior year among high school kids, and by 48% among middle school students.
And the new findings are not the first to warn about potential health risks of e-cigarettes. One 2018 study by another UNC team found that lung fluid from vapers and smokers contained elevated levels of emphysema-promoting proteases and other immune defense proteins.
Also last year, another study from Tarran's lab detected toxic compounds in commonly used vaping liquids.
This month, the U.S. Centers for Disease Control and Prevention said it is investigating more than 150 recent cases of sudden, serious lung disease in otherwise healthy young people who vape.
Patricia Folan directs the Center for Tobacco Control at Northwell Health in Great Neck, N.Y. Reviewing the new study, she said science is chipping away at the notion that vaping is "safe," or at least safer than smoking.
"Studies like this one will add to the scientific research and help educate practitioners, as well as the public, about the potential health hazards associated with vaping and dispel some of the myths surrounding their safety and effectiveness for quitting other tobacco use," Folan said.
Any health gains spurred by declines in traditional smoking might be offset by the rise in vaping, Folan added.
"The majority of emphysema cases are directly related to cigarette smoking," she said. "Smoking rates have been decreasing but vaping rates are increasing. Because of the use of these new products, the rates of emphysema may not decrease as we had hoped."
For their part, Tarran's team said they now plan to conduct a larger study of lung protease enzyme levels in hundreds of participants.
The study was published Aug. 22 in the American Journal of Respiratory and Critical Care Medicine.