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Clinical Review State of the Art Review

What are the respiratory effects of e-cigarettes?

BMJ 2019; 366 doi: (Published 30 September 2019) Cite this as: BMJ 2019;366:l5275

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The harm of e-cigarettes must be compared with the alternative for most users: continued tobacco smoking.

Gotts et al.[1] show that e-cigarettes pose a risk to respiratory health. It is now clear that people who have never smoked cigarettes should not use e-cigarettes, and that those who do – approximately 0.5% of never smokers[2] – should stop using them.

However, the great majority of regular e-cigarette users are current- or ex-smokers, most of whom are using e-cigarettes to cut down or used them to stop smoking completely.[3] Therefore, the most relevant public health consideration is the harm of e-cigarettes compared with the alternative for most users: continued tobacco smoking. This requires a dispassionate look at and accurate reporting of the available evidence.

While cessation is not the focus of the review, the abstract misleadingly reports "their effectiveness as a smoking cessation intervention…[is] highly controversial". Yet, neither the Cochrane review or NASEM report on the topic are cited.[4,5] Even before the publication of a large RCT in the NEJM, which demonstrated that participants who were offered e-cigarettes had two-fold higher quit rates than those given nicotine replacement therapy,[6] the NASEM report concluded “there is moderate evidence from randomized controlled trials that e-cigarettes with nicotine are more effective than e-cigarettes without nicotine for smoking cessation”. These findings are supported by two studies that used population data from the UK and US, published in the BMJ.[7,8]

The authors state that, “current knowledge of these effects is insufficient to determine whether the respiratory health effects of e-cigarette are less than those of combustible tobacco products.” Yet, they often report on the absolute harm of e-cigarette use, without the comparison with smoking. For instance, the authors include research showing that e-cigarette aerosol can contain the known carcinogens and toxicants acetaldehyde, acrolein, diacetyl, and formaldehyde. Yet they neglect various studies[9] showing that these chemicals are present at far lower levels in e-cigarette vapour than in cigarette smoke, when used under realistic conditions.

There is also an omission of relevant research on biomarkers of toxicant and carcinogen exposure. This work is especially useful for assessing the effect of e-cigarette use on respiratory health because, unlike animal and cell models, these studies measure toxicant exposure among real-world e-cigarette users. This research shows that long-term e-cigarettes users have substantially lower levels of these biomarkers.[10] In fact, they have similar levels to NRT-only users,[11] including for metabolites of acrolein, a known respiratory irritant, and NNK, a potent carcinogen linked to lung cancer. This provides reassurance that, when compared with smoking, e-cigarette use puts one at far lower risk of developing lung diseases associated with inhalation of these toxicants.

Further research and monitoring of the possible health effects of e-cigarettes is essential but so also are accurate statements on comparative safety. Already, the majority of smokers in England believe e-cigarettes are at least as harmful as cigarettes, a declining proportion are using them to support quitting and a growing number attempt to quit without any aid.[12] Each year, cigarettes kill 5.2 million of the 1.1 billion smokers worldwide, and another million die from second-hand exposure.[13] Misleading statements about the comparative safety of e-cigarettes may not only influence policy in a way that is not supported by evidence, but may also deter people who have struggled to stop smoking deadly cigarettes from using an effective method at helping them quit.

1. Gotts JE, Jordt S-E, McConnell R, Tarran R. What are the respiratory effects of e-cigarettes? BMJ. 2019;366:l5275. doi:10.1136/bmj.l5275
2. McNeill A, Brose LS, Calder R, Bauld L, Robson D. Vaping in England: An Evidence Update February 2019. London; 2019.
3. Action on Smoking and Health. Use of E-Cigarettes (Vaporisers) among Adults in Great Britain.; 2019. Accessed October 24, 2019.
4. Stratton K, Kwan L, Eaton D. Public Health Consequences of E-Cigarettes. (Eaton DL, Kwan LY, Stratton K, eds.). National Academies of Sciences (US); 2018. doi:10.17226/24952
5. Hartmann-Boyce J, McRobbie H, Bullen C, Begh R, Stead L, Hajek P. Electronic cigarettes for smoking cessation. Cochrane Database Syst Rev. 2016. doi:10.1002/14651858.CD010216.pub3
6. Hajek P, Phillips-Waller A, Przulj D, et al. A randomized trial of E-cigarettes versus nicotine-replacement therapy. N Engl J Med. 2019;380(7):629-637. doi:10.1056/NEJMoa1808779
7. Zhu SH, Zhuang YL, Wong S, Cummins SE, Tedeschi GJ. E-cigarette use and associated changes in population smoking cessation: Evidence from US current population surveys. BMJ. 2017;358. doi:10.1136/bmj.j3262
8. Beard E, West R, Michie S, Brown J. Association between electronic cigarette use and changes in quit attempts, success of quit attempts, use of smoking cessation pharmacotherapy, and use of stop smoking services in England: time series analysis of population trends. BMJ. 2016;354:i4645. doi:10.1136/bmj.i4645
9. Farsalinos KE, Gillman G. Carbonyl Emissions in E-cigarette Aerosol: A Systematic Review and Methodological Considerations. Front Physiol. 2018;8:1119. doi:10.3389/fphys.2017.01119
10. Chang CM, Edwards SH, Arab A, Del Valle-Pinero AY, Yang L, Hatsukami DK. Biomarkers of Tobacco Exposure: Summary of an FDA-Sponsored Public Workshop. Cancer Epidemiol biomarkers Prev. 2017;26(3):291-302. doi:10.1158/1055-9965.EPI-16-0675
11. Shahab L, Goniewicz ML, Blount BC, et al. Nicotine, Carcinogen, and Toxin Exposure in Long-Term E-Cigarette and Nicotine Replacement Therapy Users. Ann Intern Med. 2017;166(6):390. doi:10.7326/M16-1107
12. West R, Proudfoot H, Mohr G, Beard E, Brown J. Electronic Cigarettes in England - Latest Trends from the Smoking Toolkit Study.; 2019. Accessed October 24, 2019.
13. Gakidou E, Afshin A, Abajobir AA, et al. Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabolic risks or clusters of risks, 1990-2016: A systematic analysis for the Global Burden of Disease Study 2016. Lancet. 2017;390(10100):1345-1422. doi:10.1016/S0140-6736(17)32366-8

Competing interests: No competing interests

28 October 2019
Harry Tattan-Birch
Trial Coordinator
Loren Kock, Dr Lion Shahab, Prof Jamie Brown
Institute of Epidemiology and Health Care, University College London
1-19 Torrington Pl, Fitzrovia, London, WC1E 7HB