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expert reaction to research on toxin exposure of smokers, vapers and NRT users

In a new cross-sectional study publishing in the Annals of Internal Medicine scientists examined human exposure to cigarette smoke compared with e-cigarettes and nicotine replacement.


Dr Ed Stephens, Senior Research Fellow at the University of St Andrews, said:

“This is a unique study and an important contribution to the debate on e-cigarette safety compared with smoking from the perspective of biomarkers.

“This study compared toxin levels in urine and saliva taken from vapers and smokers who have engaged in either habit (or both) for at least six months.  The scientists examined the duration of human exposure to cigarette smoke compared with e-cigarettes and nicotine replacement (such as patches or gum) for much longer than any previous short term study.

“They found that people who only used nicotine replacement or e-cigarettes were exposed to a far lower level of toxins.  That won’t come as a surprise to most researchers, yet the public continues to be confused about the relative safety of e-cigarettes, with some believing they are as harmful as cigarettes.  That’s worrying.

“This paper confirms the potential benefits of e-cigarettes and contributes to the growing body of evidence that the risk from chemicals in vapour is far lower than in cigarette smoke when an e-cigarette is used as the manufacturer intended.

“This is a biomarker study, and it can’t tell us everything.  There is a huge range of brands and flavours of e-liquids on the market and we do not yet know whether some might be more toxic than others.  I would expect that in most circumstances any compounds found to have a toxic risk that we don’t already know about will be present in rather low concentrations in e-cigs and so probably make only small contributions to the overall risk, but we do not yet know this for sure.

“Slightly unexpected is the finding that combined smoking and vaping does not offer any long term health benefit while smoking continues; but if initial dual use leads to quitting altogether then the health gains could be significant.  There may be additional hazards in vaping that have yet to be discovered, but the best evidence to date should encourage smokers who are thinking of taking up vaping for health reasons to progress to stopping smoking quickly and completely, then gradually wind down their vaping.”


Jamie Hartmann-Boyce, Senior Researcher in Health Behaviours at the University of Oxford and Managing Editor of the Cochrane Tobacco Addiction Group, said:

“This is an important study in an area where further research is badly needed. Many studies which assess the safety of electronic cigarettes have done so by measuring their components in a lab, rather than measuring their impact in users. In this paper, the authors studied current smokers, vapers, and people who use nicotine replacement therapy (NRT) and compared levels of nicotine and known harmful substances between the groups.

“Nicotine levels were roughly similar in all three groups, suggesting that people achieved the levels of nicotine from using e-cigarettes or NRT that they may have formerly done by smoking. However, in vapers and NRT users (people not smoking regular cigarettes) there were lower levels of known toxins and carcinogens. This is not surprising as we know that most of the harm from smoking comes from the burning of tobacco, which doesn’t take place with NRT or electronic cigarettes. In people who continued smoking alongside vaping or using NRT, levels of harmful chemicals were similar to that in smokers who didn’t vape or use NRT.

“This was a relatively small study and only looked at people who had been using these products for six months or longer. We still need more studies on the long term safety of electronic cigarettes, but this study adds to the growing body of evidence suggesting electronic cigarettes are considerably safer than smoking regular cigarettes, as is using NRT long term. Cigarettes are uniquely deadly and smokers who switch to electronic cigarettes or long-term use of NRT should remember that the harm from cigarettes comes from the tar, and not the nicotine.


Prof. Kevin Fenton, national director of health and wellbeing at Public Health England said:

“This study provides further evidence that switching to e-cigarettes can significantly reduce harm to smokers, with greatly reduced exposure to carcinogens and toxins.  The findings also make clear that the benefit is only realised if people stop smoking completely and make a total switch.”

“The best thing a smoker can do, for themselves and those around them, is to quit now, completely and forever. E-cigarettes are the most popular quitting method in England and local stop smoking services are the most effective way to give up, with those who combine the two having some of the highest success rates.”


Prof. Peter Hajek, Director of the Tobacco Dependence Research Unit at Queen Mary University of London (QMUL), said:

“This study is important for several reasons. It confirms the common-sense expectation that switching from smoking to vaping reduces or eliminates the exposure to dangerous chemicals from tobacco smoke. It also shows that this benefit is as large as, or even larger than, switching from smoking to nicotine replacement treatment such as nicotine chewing gum or patch.

“There are some other reassuring findings there.

“If the e-liquid is over-heated, it can produce high levels of aldehydes. Despite the fact that this generates an unpleasant taste that vapers avoid, this finding has led to previous health scares. In contrast to results from frying e-liquid in a laboratory, the results from human vapers presented here show that switching from smoking to vaping not only generates no increase in aldehyde levels, but in fact leads to a dramatic reduction.

“Previously, concerns were also expressed that combining smoking and vaping could increase toxin exposure. Again, this has not been confirmed. Many smokers need a period of such ‘dual use’ before they manage to stop smoking completely and there is no sign that this process poses any risk over and above ‘only’ smoking.

“Overall, the study provides additional evidence for encouraging smokers to switch to vaping. It is unfortunate that the new European Tobacco Products Directive that submits e-cigarettes to much stricter regulation than conventional cigarettes has the opposite aim, i.e. to discourage such a switch. This makes little sense and is likely to be harmful to public health.”


* ‘Nicotine, Carcinogen, and Toxin Exposure in Long-Term E-Cigarette and Nicotine Replacement Therapy Users’ by Lion Shahab et al. published in Annals of Internal Medicine on Monday 6 February 2017.


Declared interests


Prof Hajek: “I received researcher funding from and provided consultancy to manufacturers of stop-smoking medications. He has no links with any e-cigarette manufacturers. His research into e-cigarette safety and effects has been funded by NIHR, PHE, UKCTAS and MHRA.”

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