Smoke from e-cigarettes has been found to cause lung cancer in mice, according to a study published in the American journal Proceedings of the National Academy of Sciences.
Prof Moon-shong Tang of New York University led the research in which 9 out of 40 mice (22.5 per cent) exposed to vape smoke containing nicotine for 54 weeks developed lung cancer. In contrast, none of the 20 mice exposed to nicotine-free vape smoke developed cancer.
“Tobacco smoke is among the most dangerous environmental agents to which humans are routinely exposed, but the potential of vape smoke as a threat to human health is not yet fully understood,” said Tang.
He urges caution when it comes to interpreting his study’s findings, though, as it was conducted with a relatively small sample of mice susceptible to developing cancer over their lifetimes. The mice also did not inhale the smoke in the same way a human would, but instead were surrounded by a cloud of it.
“Our study’s results in mice were not meant to be compared to human disease, but instead argue that vape smoke must be more thoroughly studied before it is deemed safe or marketed that way,” Tang said.
The study comes just weeks after vaping products have been implicated in a spate of respiratory illnesses and deaths in the US. As a result, the states of Michigan, New York, Massachusetts and Rhode Island have all enacted emergency bans on the sale of flavoured vaping products. The city of San Francisco and the country India have gone further by banning the sale of vaping products entirely.
In the UK, however, Public Health England maintains that vaping is less dangerous than smoking tobacco and an effective method to help people give up the habit. They point to the lower cap on the nicotine content of vaping products sold legally in England, and stricter regulations governing their advertising, as key reasons why the UK has not seen the same explosion in vaping that the US has.
At the root of the matter is the question of whether nicotine alone can cause cancer. Although studies over the years have produced conflicting results, the majority of researchers agree that chemicals added to tobacco leaves while they are cured can convert nicotine into nitrosamines, chemicals that are carcinogenic to mice and humans.
Aside from the connection to lung cancer, Tang’s team also found that 23 of the 40 mice (57.5 per cent) exposed to nicotine vape smoke also developed bladder hyperplasia, an increase in the reproduction rate of the organ’s cells that is often an early indication of cancer. Only 1 of the 17 mice exposed to nicotine-free vape smoke developed hyperplasia.
“Our results support the argument that the nicotine-derived changes in DNA are likely the main causes for carcinogenesis in mice exposed to vape smoke,” says New York University’s Dr Herbert Lepor, who wrote the study.
“Our next step will be to expand the number of mice studied, to shorten and prolong vape exposure time, and to further investigate the genetic changes caused by vape smoke.”
Before going freelance, Rob spent almost four years on staff at BBC Science Focus magazine subediting news, features and reviews. He's now a freelance journalist and has written about everything from electric cars to decomposing bodies… although space and speed are what fascinate him most.