Well-done study shows e-cig use associated with more quitting; needs to be considered in context of the whole literature

Shu-Hong Zhu and colleagues at UCSD just published “E-cigarette use and associated changes in population smoking cessation: evidence from US current population surveys,” a well-done sequential cross-sectional study in which they concluded that in 2014-2015 there was a substantial increase in quit attempts and successful quitting among people using e-cigarettes compared to previous years.
I was particularly struck by the care with which the authors placed their results in the context of the larger literature, including changes to the policy environment which could be affecting quit attempts, such as tax increases and the CDC TIPS from Former Smokers media campaign (which the Republicans in Congress are working to defund despite its proven success).
Needless to say, the e-cigarette enthusiasts are presenting this paper as the last word on the question of the population health effects.  In an accompanying editorial, Chris Bullen, who was much less judicious in interpreting the results than Zhu and colleagues, wrote “policy makers in countries contemplating a more restrictive approach to the regulation of e-cigarettes should pause to consider if pursuing such a course of action is the right thing to do for population health. of e-cigarettes and saying that it justifies.” In an interview with ABC, Peter Hajek went even further: "It's absolutely clear that e-cigarettes help smokers replace cigarettes."
Rather than treating this one study (or any one study) as the end-all, it needs to be interpreted in the context of the overall literature.  Before the Zhu paper was published, there were 28 studies of the relationship between e-cigarette use and smoking cessation, 20 of which showed depressed quitting and 8 of which showed improved quitting (29%, based on point estimates).  Adding the new paper to this picture brings the total number of studies to 29, with 9 showing increased quitting (31%).
So, while this study is an important contribution, on balance, the evidence still weighs against the conclusion that e-cigarettes are helping people quit on population level.
Another important element of the larger picture is the effect that e-cigarettes have on expanding the tobacco market by attracting low-risk kids to tobacco product use, including consistent evidence of a gateway effect, with kids who initiate with e-cigarettes being 3-4 times more likely to go on to cigarettes.
Here is the abstract for the paper:
Objective To examine whether the increase in use of electronic cigarettes in the USA, which became noticeable around 2010 and increased dramatically by 2014, was associated with a change in overall smoking cessation rate at the population level.
Design Population surveys with nationally representative samples.
Setting Five of the US Current Population Survey-Tobacco Use Supplement (CPS-TUS) in 2001-02, 2003, 2006-07, 2010-11, and 2014-15.
Participants Data on e-cigarette use were obtained from the total sample of the 2014-15 CPS-TUS (n=161 054). Smoking cessation rates were obtained from those who reported smoking cigarettes 12 months before the survey (n=23 270). Rates from 2014-15 CPS-TUS were then compared with those from 2010-11 CPS-TUS (n=27 280) and those from three other previous surveys.
Main outcome measures Rate of attempt to quit cigarette smoking and the rate of successfully quitting smoking, defined as having quit smoking for at least three months.
Results Of 161 054 respondents to the 2014-15 survey, 22 548 were current smokers and 2136 recent quitters. Among them, 38.2% of current smokers and 49.3% of recent quitters had tried e-cigarettes, and 11.5% and 19.0% used them currently (every day or some days). E-cigarette users were more likely than non-users to attempt to quit smoking, 65.1% v 40.1% (change=25.0%, 95% confidence interval 23.2% to 26.9%), and more likely to succeed in quitting, 8.2% v 4.8% (3.5%, 2.5% to 4.5%). The overall population cessation rate for 2014-15 was significantly higher than that for 2010-11, 5.6% v 4.5% (1.1%, 0.6% to 1.5%), and higher than those for all other survey years (range 4.3-4.5%).
Conclusion The substantial increase in e-cigarette use among US adult smokers was associated with a statistically significant increase in the smoking cessation rate at the population level. These findings need to be weighed carefully in regulatory policy making regarding e-cigarettes and in planning tobacco control interventions.
The full citation is Shu-Hong Zhu, Yue-Lin Zhuang, Shiushing Wong, Sharon E Cummins, Gary J Tedeschi.  E-cigarette use and associated changes in population smoking cessation: evidence from US current population surveys. BMJ 2017; 358 doi: https://doi.org/10.1136/bmj.j3262 (Published 26 July 2017) Cite this as: BMJ 2017;358:j3262


People who quit with ecigs may have more relapse

Zhu and colleagues' conclusion that e-cigarettes were associated with significantly more quitting smoking was limited to recent (in the last year) quitters.
Table 3 of their paper also reports results for people who quit smoking more than 1 year ago.  I analyzed those data and found that among people who quit smoking 1-5 years ago, people who currently used e-cigarettes were about 30% less likely to still be nonsmokers than people who did not use e-cigarettes.
This result suggests to me that, among people who quit smoking, continuing to use e-cigarettes is associated with more relapse to cigarettes.
This is a question that merits more attention in longitudinal studies.  (Zhu et al is cross-sectional.)  But, in the meantime, policymakers need to consider the possibilty of increases in long-term relapse to smoking among e-cigarette users.  This is also another reason to tell people who manage to quit smoking using e-cigarettes (or think they accomplished it with e-cigarettes) that they need to stop the e-cigarettes as soon as possible, too.