Vaping damages DNA in mice, which 'may increase cancer risk'

Wednesday January 31 2018

"Vaping causes cancer, new study warns," is the alarming – yet incorrect – headline from the Mail Online.

Researchers in the US found that cells of mice exposed to e-cigarette vapour for 3 hours a day showed signs of DNA damage, and impaired ability to repair that damage, in comparison with mice that weren't exposed to the vapour. Human cells bathed in a nicotine solution showed similar results.

However, animal studies and laboratory tests on cells do not tell us about the effects of inhaling e-cigarette vapour on humans. Importantly, the study didn't compare e-cigarette vapour with tobacco smoke, so we don't know how, or even if, the amount of cell damage varies between vapour and tobacco smoke. We also don't know whether the DNA damage in the mice would have led to cancer if the experiments had run for longer.

E-cigarette vapour includes nicotine dissolved in a solvent, which is vapourised into a fine mist and then inhaled. While nicotine isn't harmless, it's much less dangerous than some of the other chemicals in tobacco smoke, such as tar and carbon monoxide.

This study suggests that e-cigarettes may not be risk-free – and nicotine is of course highly addictive – but it doesn't change the likelihood that they are far less harmful than smoking tobacco.

Ideally, you should be using e-cigarettes as a tool to gradually reduce and then quit nicotine, rather than as a long-term alternative to smoking tobacco. Other forms of nicotine replacement therapy, such as patches and gum, are also available.

Read more about stop smoking treatments.

Where did the story come from?

The study was carried out by researchers from New York University School of Medicine and funded by the US National Institutes of Health. It was published in the peer-reviewed medical journal PNAS, which is open-access, meaning the article is free to read online.

While the Mail Online took an alarmist angle on the story, some of the UK media adopted a more measured tone. Sky News and The Guardian carried responsible reports that correctly stated what the researchers had done and the results they found. They also included comments from experts who pointed out the known dangers of tobacco smoke and that previous studies have found much less risk from e-cigarettes.

What kind of research was this?

This was a mixture of animal and in vitro experiments – where experiments are carried out on human cells grown in the laboratory. Animal and in vitro experiments are useful ways to explore theories but often tell us little about what happens in living humans.

What did the research involve?

For the animal experiments, researchers exposed some mice to e-cigarette vapour for 3 hours a day, 5 days a week for 12 weeks – which they claimed to be equivalent to light e-cigarette use in humans for 10 years, although they didn't explain how they calculated this – while other mice not exposed to e-cigarette vapour acted as a control.

They then conducted experiments on cells from the mice's hearts, lungs and bladders. They looked to see whether the cells' DNA showed particular types of damage or mutation. They then looked to see whether cells exposed to e-cigarette vapour were able to repair experimentally induced damage and measured the levels of the proteins needed to carry out the repair.

The experiments were repeated on human lung and bladder cells that had been exposed to different concentrations of nicotine solution.

None of the experiments compared tobacco smoke with e-cigarette vapour or nicotine solution.

What were the basic results?

The mouse experiments found:

  • mutations in DNA in cells from the lungs, bladders and hearts of mice that had been exposed to e-cigarette vapour, at higher levels than in mice exposed only to filtered air
  • less DNA repair activity in cells from the lungs of mice exposed to e-cigarette vapour in comparison with mice exposed to filtered air
  • lower levels of 2 types of proteins that aid DNA repair in cells from the lungs of mice exposed to e-cigarette vapour in comparison with mice exposed to filtered air

The experiments using human lung and bladder cells showed more DNA mutations in cells exposed to higher concentrations of nicotine solution. These cells also showed less evidence of DNA repair activity.

How did the researchers interpret the results?

The researchers said: "Based on these results, we propose that ECS [electronic cigarette smoke] is carcinogenic and that e-cig smokers have a higher risk than non-smokers to develop lung and bladder cancer and heart diseases."

They also said that the length of time it takes for cancer to develop in humans means that animal and in vitro cell experiments are valid ways to investigate cancer risk.

Conclusion

The study's findings tell us that e-cigarette vapour may not be risk-free and that nicotine solution may cause cell DNA damage that has the potential to become cancer. However, there's a big difference between seeing these results in mice and cultured cells, and knowing how it affects people using e-cigarettes.

The missing factor in the study was the comparative risk of damage from tobacco smoke. As well as nicotine, tobacco smoke contains hundreds of chemicals known to cause cancer. Removing those chemicals means that nicotine is the main remaining risk from vaping.

This study suggests that inhaling nicotine may not be risk-free, but it does not change the fact that it's likely to be much less harmful than inhaling all the cancer-inducing chemicals in tobacco smoke.

The study had various limitations:

  • results from animal studies often don't translate into results in humans
  • results from isolated in vitro cell cultures, even from human cells, often don't translate into what happens in the human body
  • the mouse exposure to e-cigarette vapour was said to be comparable with 10 years' light e-cigarette use, but administering this over 12 weeks would mean the mice were exposed to very high levels of e-cigarette vapour – this concentrated exposure may have had a bigger effect on DNA repair than much lower exposures would have

If you're using e-cigarettes to help you stop smoking, your health is far more likely to benefit from stopping smoking tobacco than it is to suffer from e-cigarette vapour. However, if you don't smoke tobacco, no one would suggest it's a good idea to take up e-cigarettes.

Find out more about using e-cigarettes to stop smoking.

Analysis by Bazian
Edited by NHS Website