In laboratory tests, mice exposed to e-cig vapour had higher levels of DNA damage in the heart, lungs and bladder than those just breathing clean air.
The damage was seen both to DNA and its ability to fix itself, making cells more likely to mutate and develop into cancer, said lead researcher Moon-shong Tang, a professor of environmental medicine at New York University School of Medicine.
But new evidence suggests nicotine itself and some of its by-products may also cause cancer. "It's certainly concerning, and certainly gives pause if one were to say e-cigarettes were safe and could be used by all people without consequences". Instead they contain nicotine, which is what keeps people addicted, but is not responsible for the major health harms from smoking. To simulate the effects of long-term e-cigarette use on the body, researchers exposed mice to ECS over a 12-week period.
Dr Tang highlighted the increasing popularity of e-cigarettes and vaporisers in recent years as motivation for the research. Nitrosamines are known to cause tumor formation when animals are exposed to them, and some nitrosamines, such as nitrosamine ketone (NNK) are then broken down further into chemicals like methyldiazohydroxide (MDOH) which can actually bind to and alter DNA directly. "Nicotine with e-cigarette solvent caused the same damage as nicotine alone".
Similar results were seen in cultured human lung and bladder cells exposed to nicotine.
They subjected mice and human cells to the vapor. E-cigarettes are often advertised as a safer alternative to cigarettes, as they don't include the more than 7,000 extra chemicals that are produced when tobacco is burned.
One scientist not involved with the research pointed to what he considered a shortcoming in the study.
There is no safe level of smoking, as even one cigarette a day increases by about 50% the risk for coronary artery disease and 30% for stroke, according to a new British scientific study. He's chair of epidemiology at the University of South Carolina's Arnold School of Public Health.
Nevertheless, an important point to consider is that other health risks associated with smoking tobacco are most definitely avoided by e-cigarettes. "The magnitude of how much a reduction in risk that would be is unknown", he said.
"Research in people has shown that those who make a complete switch from smoking tobacco to e-cigarettes can significantly reduce their exposure to key harmful chemicals in tobacco smoke". Details of the study are reported in the journal Proceedings of the National Academy of Sciences. The mice were exposed to high levels of e-cigarette smoke and the effects may be very different in people who inhale nicotine from vaping, critics caution.