Meta-analyses find vaping leads to smoking among young people and former smokers

This post highlights scientific reviews about the relationship between vaping and smoking that have been published since our previous summaries (in January 2021 and April 2021). 

More evidence that vaping puts young people at greater risk of smoking

An Australian team of researchers has provided a new systematic review and meta-analysis of studies exploring whether e-cigarette use is a risk factor for subsequent cigarette smoking in young people. In this study, published in PLOS one last month, Sze Lin Yoong and colleagues restricted their analysis to longitudinal studies only, thus strengthening the certainty of the findings. Their meta-analysis of 17 such studies of e-cigarette use at baseline and subsequent ever cigarette use (published before October 2020) found a relative risk of cigarette uptake of 3.01. All 17 studies showed a positive relationship. 

This study builds on the conclusions of other recent meta-analyses, including those published last year by British researchers (Kouja et al. based on evidence up to November 2018) and another Australian team (Baenziger et al. based on evidence up to April 2020). Multiple studies have now confirmed that adolescents who use e-cigarettes are at least three times more likely to take up smoking than non-users of e-cigarettes.

And newer studies provide consistent results ...

After the October 2020 cut-off date for the Yoong meta-analysis, three more longitudinal studies appeared were published that provide consistent conclusions.

In July 2021, Jeremy Staff and colleagues reported on their study using longitudinal data on British youth who were questioned at age 14 and followed at age 17. They found that young people who were using e-cigarettes at age 14, but not smoking, were more than five times more likely to have started smoking tobacco cigarettes by age 17.  The reverse was true too. Those who started smoking tobacco cigarettes at age 14 were three times more likely take up e-cigarettes by age 17.  Their results counter the proposition that the young people who vape would otherwise be smokers (the 'common liability' theory) as they found distinct risk factors for tobacco-use and vaping.

Also in July 2021, a paper written by the Netherlands' research team lead by Thomas Martinelli  reported on e-cigarette use and tobacco smoking among Dutch-speaking high school students in the Netherlands and Belgium. This longitudinal study collected follow-up information after six and twelve months and found that those who were using e-cigarettes were 5.63 times more likely to be using tobacco a year later.  They also found that those who were smoking tobacco were 3 times more likely to be using e-cigarette at the year's end. These findings are very like those of British youth reported by Staff et al., cited above. 

A few weeks earlier, Elizabeth Hair and colleagues reported on a longitudinal study of youth and young adutls (15-21 year-olds in 2017) who were contacted after one year. This study found that users of e-cigarettes in 2017 were more than three times more likely to become users of cigars, little cigars or cigarillos (CLCCs) by 2018.  Young people who were cigarette smokers or marijuana users in 2017 were also more likely to become users of CLCCs by 2018.

Evidence that vaping puts former smokers at greater risk of relapsing 

Health authorities hold differing views on whether or not e-cigarettes help smokers quit. For example, Health Canada advises that vaping products are "linked to improved rates of success", but U.S. health authorities (eg U.S. Surgeon General) has found there is "inadequate evidence to conclude that e-cigarettes, in general, increase smoking cessation." Since our last review of this topic in April , the Cochrane review has updated its review and concluded there are reasons to be "moderately confident" that e-cigarettes outperformed NRT in helping people quit for at least 6 months. Because this review considered only random clinical trials and did not look at studies of real-world conditions, it is consistent with the conclusions of recent meta-analyses which found e-cigarettes are effective in clinical settings, but not when sold as consumer products.

But what about those who successfully quit smoking and have remained non-smokers for a year or more? Are some of them tempted to try e-cigarettes? If they do so, are they more or less likely to relapse to tobacco use?

These questions were recently addressed by a Brazilian research team led by Laura Barufaldi. Their search for all papers which examined this phenomenon resulted in only three studies which met their inclusion criteria.

The largest (and thus most influential) of these was by American researchers Hongying Dai and Adam Leventhal who used data from the U.S. longitudinal study on smoking behaviour (the Population Assessment of Tobacco and Health, or PATH Study). From this study they identified people who at the time of the interview had quit smoking more than 12 months previously and then looked for their smoking status one year later. They found that those who had taken up vaping after quitting smoking were 2- 4 times more likely to have relapsed to tobacco smoking.

The other papers confirmed and reinforced those conclusions: Smoking relapse was twice as likely among people who had quit smoking but subsequently started using e-cigarettes.

Implications for public health

Adolescents who never smoked but start vaping are at least three times more likely to start smoking than adolescents who don't try vaping.
• Some former smokers take up e-cigarettes.  If they do so, they are twice as likely to relapse to smoking as former smokers who don't vape.
• E-cigarettes may help some people quit smoking as part of a supervised intervention. In the majority of cases, when acquired and used as consumer products, they do not increase the likelihood of successful quitting

Publications cited:

Baenziger ON, Ford L, Yazidjoglou A, et al. E-cigarette use and combustible tobacco cigarette smoking uptake among non-smokers, including relapse in former smokers: umbrella review, systematic review and meta-analysis, BMJ Open 2021

https://bmjopen.bmj.com/content/11/3/e045603

Barufaldi LA, Guerra RL, de Albuquerque RCR, et al. Risk of smoking relapse with the use of electronic cigarettes: A systematic review with meta-analysis of longitudinal studies. Tob Prev Cessat. 2021;29:29. Published 2021 Apr 27. doi:10.18332/tpc/132964

Dai H, Leventhal AM. Association of electronic cigarette vaping and subsequent smoking relapse among former smokers. Drug Alcohol Depend. 2019;199:10-17. 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6743978/

Hair EC, Kreslake JM, Mowery P et al. A longitudinal analysis of e-cigarette use and cigar, little cigar or cigarillo initiation among youth and youth adults: 2017–2019. Drug and Alcohol Dependence,

Volume 226, 2021.
https://pubmed.ncbi.nlm.nih.gov/34218009/

Hartmann-Boyce J, McRobbie H, Butler AR, Lindson N, Bullen C, Begh R, Theodoulou A, Notley C, Rigotti NA, Turner T, Fanshawe TR, Hajek P. Electronic cigarettes for smoking cessation. Cochrane Database Syst Rev. 2021 Sep 14;9(9) https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD010216.pub6/full

Khouja JN, Suddell SF, Peters SE, Taylor AE, Munafò MR. Is e-cigarette use in non-smoking young adults associated with later smoking? A systematic review and meta-analysis. Tob Control. 2020 Mar 10;30(1):8–15. doi: 10.1136/tobaccocontrol-2019-055433. https://pubmed.ncbi.nlm.nih.gov/32156694/

Martinelli T, Candel MJJM, de Vries H, et al. Exploring the gateway hypothesis of e-cigarettes and tobacco: a prospective replication study among adolescents in the Netherlands and Flanders. Tobacco Control Published Online First: 05 July 2021. https://tobaccocontrol.bmj.com/content/early/2021/08/18/tobaccocontrol-2021-056528

Staff, J., Kelly, B. C., Maggs, J. L., and Vuolo, M. (2021) Adolescent electronic cigarette use and tobacco smoking in the Millennium Cohort Study. Addiction, https://onlinelibrary.wiley.com/doi/10.1111/add.15645

Yoong SL,  Hall A, Turon H et al. Association between electronic nicotine delivery systems and electronic non-nicotine delivery systems with initiation of tobacco use in individuals aged < 20 years. A systematic review and meta-analysis. Plos One September 8, 2021

https://journals.plos.org/plosone/article/metrics?id=10.1371/journal.pone.0256044