"These results indicate that nicotine nitrosation occurs in vivo in mice and that E-cigarette smoke is carcinogenic to the murine lung and bladder and harmful to the murine heart".
In the paper, Tang and his colleagues concede that "it takes decades for carcinogen exposure to induce cancer in humans, [so] for decades to come there will be no meaningful epidemiological study to address the carcinogenicity of [e-cigarette smoke]".
A huge, landmark research paper this month analysed 800 previous studies into the health effects of e-cigarettes - and found that they are far less unsafe than cigarettes. Research like this is important, but this lab study only looked at the effects of e-cigarette smoke on cells and on mice, which means it's not possible to draw any conclusions from this about how e-cigarettes might affect people in real life. The researchers conducted the study over a 12-week period.
Researchers at New York University exposed mice to e-cigarette vapour (actually heat-generated aerosol that contains nicotine along with some organic solvents) and compared them to a control group just given filtered air. Others say that the risks of vaping are unclear.
In 2016, the FDA finalized a rule extending its regulatory authority to all tobacco products, including e-cigarettes, cigars, as well as hookah and pipe tobacco, as part of its goal to improve public health.
The problem comes when trying to gauge how much of an added risk e-cigarettes pose to your health. Results also demonstrated that vaping may be less addictive than smoking, as shown by longer delay times in the morning before vaping and a trend of reducing nicotine levels in e-cigarette liquid over time.
The study was published January 29 in the Proceedings of the National Academy of Sciences.
The 600-page report by America's National Academy of Sciences, Engineering and Medicine (an independent government body) says that smokers who switch to e-cigarettes will benefit.
The researchers said that if the findings will be confirmed in future studies, it could mean that e-cigarettes, always been considered to be the safer alternative to traditional cigarette and tobacco products, also carry cancer risk through the nicotine that they deliver. A study a year ago looked at the effects of e-cigarettes in what they defined as "long-term users" (around 17 months).