Intended for healthcare professionals


Evidence about electronic cigarettes: a foundation built on rock or sand?

BMJ 2015; 351 doi: (Published 15 September 2015) Cite this as: BMJ 2015;351:h4863

Re: Evidence about electronic cigarettes: a foundation built on rock or sand?

McKee and Capewell present to The BMJ their second letter criticizing the Public Health England (PHE) report [1], after a similar letter submitted to Lancet [2]. Ironically, the latter letter was titled: "Electronic cigarettes: we need evidence, not opinions". The irony is that a search on Pubmed with the terms "McKee M" as author and "e-cigarettes" or "electronic cigarettes" as title and/or abstract term found 5 articles, all of which are opinion pieces [2-6]. Although such comments can be constructive and substantial, repeatedly using conflicts of interest as the main argument is creating a few problems:

1. It is counterproductive and a sign of weakness. Most of the criticism is not at all related to the methodology, scientific findings and presentation or interpretation of the data. It adds nothing to the scientific debate. It only focuses on conflicts that supposedly influence the results. Obviously, it is impossible for any research study or report to present the conflicts of interest of all authors of every study they use as reference.

2. It represents an attempt for selective censorship. By solely focusing on the already-declared funding sources of some authors in the study by Nutt et al. [7], they indirectly but clearly imply those authors have manipulated or mispresented evidence due to the financial conflicts. Thus, they try to discredit their work. Unfortunately, they provide no evidence for data manipulation. Additionally, this is insulting for the 10 authors who did not report any potential conflicts of interest. The criticism was related only to the assessment of e-cigarette relative risk only and not to other study aspects (e.g. tobacco cigarettes or nicotine replacement therapies relative risk). Interestingly, a study using similar methodology to assess the impact of plain packaging was widely accepted by the tobacco control community without any criticism [8].

McKee and Capewell challenge the efficacy of e-cigarettes as smoking substitutes, citing a recent Cochrane review report [9]. E-cigarettes are not used as therapeutic products; they provide pleasure to the user and substitute one behavioural habit (smoking) with another (e-cigarette use). The large selection of products serves the increased demand of the adult users to satisfy their personal preference and need [10]. Randomized studies which flatten personal preference by providing a single product to all participants are not expected to present the true potential of e-cigarettes as smoking substitutes. Such studies should either be avoided or performed in an unconventional manner (e.g., allowing participants to make their choice through a large list of different products).

It would be welcomed but unrealistic to expect that e-cigarettes could be 100% successful in smoking cessation. McKee and Capewell used a simplistic approach, considering dual use as the added use of two harmful products without considering the relative risk of the two products and the amount of use of each product. Their view is based on studies finding no benefit when smoking consumption was reduced [11]. Such studies did not account for the dynamic nature of smoking consumption (reducing consumption may be temporary and may be followed by relapse to past consumption), and the dynamic nature of smoking patterns (compensatory smoking may result in similar toxin exposure despite smoking fewer cigarettes). Evidence has shown that smoking consumption is directly related to disease incidence [12]. Dual users of tobacco and e-cigarettes have partially substituted nicotine intake from smoking with nicotine intake from e-cigarettes. Thus, it is highly likely that a significant reduction in smoking consumption could result in significant health improvements in those unable to completely quit, by avoiding compensatory smoking. In fact, a recent study found a significant reduction in toxin exposure for dual users [13]. Before this issue is further explored in depth, it is irresponsible to discourage smokers who have significantly reduced smoking consumption with the use of e-cigarettes.

McKee and Capewell suggest the application of the precautionary principle in e-cigarettes since they “can hardly be considered harmless”. To set things straight, no scientist has ever suggested that e-cigarettes are absolutely harmless, in the same way that medications and many daily consumer products, food products and environmental air are not absolutely harmless. A classic example showing the vagueness of the term “harmless” (or “absolutely safe”, which is also commonly used) is regulation about water. According to the US Environmental Protection Agency, water may contain more than 80 toxic, carcinogenic and radioactive contaminants [14]; however, it is considered safe as long as those compounds are present in low levels. Application of the precautionary principle is justified on the basis of threats of serious and irreversible damage, even when there is “lack of full scientific certainty” about this damage. There has been a lot of criticism about the precautionary principle [15-18] but, in any case, the application of this principle is justified only when there is at least some evidence of risk or harm. There is currently no evidence that non-smoking adults and youth are using them regularly or that they have become a gateway to smoking. Instead, we are witnessing a continuous decline on smoking rates [19]. Monitoring of use by non-intended population is definitely needed, but there is no justification for applying the precautionary principle.

In an environment of controversy and confusing information that is communicated to the society, especially to smokers, about e-cigarettes, PHE made a decisive step to put an end on confusion. Obviously, their estimate of e-cigarettes being 95% less harmful than smoking was not based solely on the study by Nutt et al. [7] but on a large body of evidence showing that most toxic chemicals present in tobacco cigarette smoke are either completely absent from e-cigarette aerosol or present at minimal levels (usually much lower than 5%) [20]. This is an honest and evidence-based estimation, which is necessary to properly guide smokers into making informed decisions until long-term epidemiological data become available. Any criticism for research is obviously welcomed, but the discussion should be evidence-based rather than focusing on ideological opposition, prejudice and a useless hunt for the “ghost” of conflict of interest.

1. McKee M, Capewell S. Evidence about electronic cigarettes: a foundation built on rock or sand? BMJ 2015;351:h4863
2. McKee M, Capewell S. Electronic cigarettes: we need evidence, not opinions. Lancet. 2015 Sep 4. doi: 10.1016/S0140-6736(15)00146-4.
3. McKee M, Chapman S, Daube M, Glantz S. The debate on electronic cigarettes. Lancet. 2014 Dec 13;384(9960):2107.
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6. McKee M. E-cigarettes and the marketing push that surprised everyone. BMJ. 2013 Sep 26;347:f5780.
7. Nutt DJ, Phillips LD, Balfour D, et al. Estimating the harms of nicotine-containing products using the MCDA approach. Eur Addict Res 2014;20:218-225.
8. Pechey R, Spiegelhalter D, Marteau T. Impact of Plain Packaging of Tobacco Products on Smoking in Adults and Children: An Elicitation of International Experts Estimates BMC Public Health 2013;13:18.
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11. Godtfredsen NS, Holst C, Prescott E, et al. Smoking reduction, smoking cessation, and mortality: a 16-year follow-up of 19,732 men and women from the Copenhagen Centre for Prospective Population Studies. Am J Epidemiol 2002;156:994-1001.
12. Teo KK, Ounpuu S, Hawken S, et al.; INTERHEART Study Investigators. Tobacco use and risk of myocardial infarction in 52 countries in the INTERHEART study: a case-control study. Lancet. 2006 Aug 19;368(9536):647-658.
13. McRobbie H, Phillips A, Goniewicz ML, Smith KM, Knight-West O, Przulj D, Hajek P. Effects of switching to electronic cigarettes with and without concurrent smoking on exposure to nicotine, carbon monoxide, and acrolein. Cancer Prev Res (Phila). 2015 Sep;8(9):873-878.
14. Environmental Protection Agency. Drinking Water Contaminants. Available at: (accessed on September 16, 2015).
15. Peterson M. The precautionary principle should not be used as a basis for decision-making. Talking point on the precautionary principle. EMBO Rep. 2007 Apr;8(4):305-8.
16. Goldstein BD, Carruth RS. Implications of the precautionary principle: is it a threat to science? Int J Occup Med Environ Health. 2004;17(1):153-61.
17. ter Meulen RH. The ethical basis of the precautionary principle in health care decision making. Toxicol Appl Pharmacol. 2005 Sep 1;207(2 Suppl):663-7.
18. Peterson M. The precautionary principle is incoherent. Risk Anal. 2006 Jun;26(3):595-601.
19. Arrazola RA, Singh T, Corey CG, Husten CG, Neff LJ, Apelberg BJ, et al. Centers for Disease Control and Prevention (CDC). Tobacco use among middle and high school students - United States, 2011-2014. MMWR Morb Mortal Wkly Rep. 2015 Apr 17;64(14):381-385.
20. Farsalinos KE, Polosa R. Safety evaluation and risk assessment of electronic cigarettes as tobacco cigarette substitutes: a systematic review. Ther Adv Drug Saf. 2014 Apr;5(2):67-86.

Competing interests: A small minority of my studies on e-cigarettes were performed using unrestricted funds provided to the institution Onassis Cardiac Surgery Center) by e-cigarette companies.

16 September 2015
Konstantinos Farsalinos
Onassis Cardiac Surgery Center
Sygrou 356, Kallithea 17674, Greece