As more studies are published on the link between youth e-cigarette use and subsequent cigarette smoking youth, people continue publish meta-analyses summing up the results. The latest such meta-analysis, recently published in PLOS One by Sze Lin Yoong and colleagues, “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,” reported the pooled results for 23 studies of youth up to age 20. They found that, among youth who had never smoked a cigarette at baseline, the risk of smoking at followup was about tripled. The adjusted risk ratios for ever cigarette smoking was 3.01 (95% CI: 2.37 to 3·82; p<0·001) and current smoking was 2.56 (95% CI: 1·61 to 4·07; p<0·001) at follow up.
Yoong and colleagues limited themselves to longitudinal studies where people are followed forward in time. Baseline data were collected between 2013 and 2016. Their analysis included studies from the US (n = 13), Germany (3), UK (2), Canada (1), Mexico (1), Netherlands ( 1) and Scotland (1), Finland (1), Taiwan (1), and Romania (1).
As the earlier meta-analyses found all the individual studies found elevations in risk, as illustrated in the graph above for adjusted risk ratios for the association between ever e-cigarette use at baseline and subsequent ever cigarette use at follow-up.
These results are similar to the earlier meta-analysis by Khouja et al that found an adjusted odds ratio for smoking of 2.92 (95% CI 2.30 to 3.71) based on 17 studies (from the US [n=10], Germany , UK , Canada , Mexico , and Netherlands ) that included people up to age 30. (Risk ratios (also called relative risks) and odds ratios are different measured of association, but the OR approximates the RR.) Indeed, the new Yoong et al results are not all that different from the 2018 analysis by the National Academy of Medicine which found an adjusted OR for smoking at followup of 3.50 (95% CI 2.38 to 5.16) based on the first 7 studies. The fact that this association is so stable as more studies are completed in more places around the world using slightly different methodologies is strong evidence that the gateway effect from, e-cigarettes to combusted cigarettes is real.
The gateway e-cigarettes provide to cigarette smoking is not the only way that e-cigarettes are worsening the tobacco epidemic. Perhaps even more important is the fact that e-cigarettes are attracting millions of youth to nicotine addiction who would be unlikely to ever use a cigarette, with the result that even though youth cigarette smoking is still falling, total tobacco product use is way up, driven mostly by e-cigarettes. This effect would be a serious public health problem without ever considering the fact that many of these kids go on to cigarettes.
Here is the abstract for the new Yoong et al paper:
Background: This systematic review described the association between electronic nicotine delivery systems and electronic non-nicotine delivery systems (ENDS/ENNDS) use among non-smoking children and adolescents aged <20 years with subsequent tobacco use.
Methods: We searched five electronic databases and the grey literature up to end of September 2020. Prospective longitudinal studies that described the association between ENDS/ENNDS use, and subsequent tobacco use in those aged < 20 years who were non-smokers at baseline were included. The Joanna Briggs Institute Critical Appraisal Checklist was used to assess risk of bias. Data were extracted by two reviewers and pooled using a random-effects meta-analysis. We generated unadjusted and adjusted risk ratios (ARRs) describing associations between ENDS/ENNDS and tobacco use.
Findings: A total of 36 publications met the eligibility criteria, of which 25 were included in the systematic review (23 in the meta-analysis) after exclusion of overlapping studies. Sixteen studies had high to moderate risk of bias. Ever users of ENDS/ENNDS had over three times the risk of ever cigarette use (ARR 3·01 (95% CI: 2·37, 3·82; p<0·001, I2: 82·3%), and current cigarette use had over two times the risk (ARR 2·56 (95% CI: 1·61, 4·07; p<0·001, I2: 77·3%) at follow up. Among current ENDS/ENNDS users, there was a significant association with ever (ARR 2·63 (95% CI: 1·94, 3·57; p<0·001, I2: 21·2%)), but not current cigarette use (ARR 1·88 (95% CI: 0·34, 10·30; p = 0·47, I2: 0%)) at follow up. For other tobacco use, ARR ranged between 1·55 (95% CI 1·07, 2·23) and 8·32 (95% CI: 1·20, 57·04) for waterpipe and pipes, respectively. Additionally, two studies examined the use of ENNDS (non-nicotine devices) and found a pooled adjusted RR of 2·56 (95% CI: 0·47, 13·94, p = 0.035).
Conclusion: There is an urgent need for policies that regulate the availability, accessibility, and marketing of ENDS/ENNDS to children and adolescents. Governments should also consider adopting policies to prevent ENDS/ENNDS uptake and use in children and adolescents, up to and including a ban for this group.
The full citation is Yoong SL, Hall A, Turon H, Stockings E, Leonard A, Grady A, Tzelepis F, Wiggers J, Gouda H, Fayokun R, Commar A, Prasad VM, Wolfenden L. 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. 2021 Sep 8;16(9):e0256044. doi: 10.1371/journal.pone.0256044. PMID: 34495974; PMCID: PMC8425526. It is available here.