New research in mice suggests that long-term exposure to vaping liquids that contain nicotine greatly increases the risk of cancer.
After breathing in the vapor for 20 hours a week for more than a year, 22.5% of the mice had cancerous tumors in the lining of the lungs, and 57.5% developed growths in their bladder tissue that can be precursors to cancer.
Meanwhile, only 5.6% of mice in a control group that breathed only filtered air wound up with lung tumors, and none of them had growths in their bladders. In addition, a group of mice exposed to aerosolized vaping chemicals without nicotine developed no lung tumors, and just 6.3% of them had precancerous bladder growths.
The scientists who conducted the study stressed that much more research is needed to know whether vaping leads to cancer in humans. But they hope their findings, published Monday in the journal Proceedings of the National Academy of Sciences, will make people think twice before trying e-cigarettes, which are widely perceived by teenagers and young adults as a safe alternative to smoking.
"Right or wrong, millions of young people are using these right now, and the long-term, population-wide studies won't be able to report out results for another decade," said study leader Moon-Shong Tang, an environmental health expert at NYU School of Medicine.
"We needed credible evidence to guide people in their choices, and it is unambiguous that nicotine alone will cause damage to the cells that make up organs, including lungs," said Tang, who has studied how tobacco smoke promotes cancers of the lung and bladder. "Now, we can try to find measures to prevent incidents of e-cigarettes causing cancer."
Vaping has been linked to heart attacks, seizures and burns from exploding devices. And a growing outbreak of at least 1,080 vaping-related lung injuries serves as a stark reminder that it's too soon to know whether e-cigarettes are a safe alternative to smoking.
To get a better idea of the long-term effects of nicotine, Tang and his collaborators exposed 45 mice to an aerosol of nicotine dissolved in isopropylene glycol and vegetable glycerin, a common vehicle for vaping liquids. Another group of 20 mice was exposed to the same vehicle without nicotine. For 54 weeks, the animals were subjected to the aerosol mixes for four hours per day, five days per week.
A third group of 20 mice spent their time in a room with ambient filtered air. (The study was limited to 54 weeks in order to minimize the effects of age-related cancers that could have cropped up occurred regardless of exposure to e-cigarette vapor.)
Five mice in the group exposed to nicotine died over the course of the year. So did two of the mice in each of the other groups.