March 27, 2023

expert reaction to study of teen vaping and persistent smoking in the US

A study, published in JAMA Network Open*, has looked at any link between teen vaping levels and persistent adolescent cigarette smoking in the US.

Prof Lion Shahab, Professor of Health Psychology and Co-Director of the UCL Tobacco and Alcohol Research Group, University College London (UCL), said:

“This paper, using data from several waves of the longitudinal PATH study in the US, attempts to reconcile contradictory findings in the literature which show that while use of e-cigarettes is associated with subsequent cigarette smoking in youth, adolescent smoking rates have continued to decline at the same that e-cigarette use by youth increased dramatically in the US. This helpful analysis replicates the longitudinal association of e-cigarette use with later smoking initiation and continued smoking, suggesting there is a greater likelihood to start and to continue to smoke if youth had been an ever or current e-cigarette user at an earlier wave. Crucially, however, it also shows that, irrespective of e-cigarette use, very few adolescents initiate smoking later on (around 4%) and even fewer continue to smoke (depending on the measure of how established smoking is, this was as low as 0.2% for daily smoking in this sample). 

“This means that when results are analysed statistically, the likelihood/odds ratios calculated to assess risk may overinflate actual effects because the even rate (smoking initiation or continued smoking) is so rare. By contrast, absolute risk differences will be less biased by this low event rate and, in fact, show no strong evidence of an effect of e-cigarette use on subsequent smoking. To put this into context, overall 1.5% of adolescents who had never smoked at the earlier wave were “established” smokers by later waves (i.e., had started to smoke since baseline and had smoked in the past 30 days). This figure was 6% for ever users of e-cigarettes at baseline and 1.1% for never users of e-cigarettes at baseline. Adjusting for confounders that are associated with smoking in general, this produces an odds ratio of 1.81 (meaning there is a 81% higher likelihood of starting to smoke later on if adolescents used an e-cigarette at baseline). However, because so few adolescents actually started to smoke in both groups (e-cigarette users and non-users), the absolute risk difference when adjusting for all kinds of other factors that lead to smoking, was only 0.88% and not significant. This means that even though e-cigarettes relatively speaking are associated with later smoking compared with not using them, because so few adolescents start smoking, irrespective of their e-cigarettes use, at population level e-cigarette use will not have had a noticeable impact on smoking rates in absolute terms. 

“Importantly, this study cannot tell us what adolescents that started using e-cigarettes would have done in the absence of e-cigarettes. It is conceivable that these youth would have started using cigarettes instead anyway, and at possibly much higher rates, had they not opted to use e-cigarettes instead. Whatever the case may be, it is reassuring to see that whether or not adolescents use e-cigarettes, cigarette use, which is far more harmful, is becoming increasingly rare and regular, daily use has become virtually non-existent among youth in the United States.”

* ‘Association of Electronic Cigarette Use by US Adolescents With Subsequent Persistent Cigarette Smoking’ by Ruoyan Sun et al. was published in JAMA Network Open at 4pm UK time on Monday 27^th March.

DOI: 10.1001/jamanetworkopen.2023.4885 

Declared interests

Prof Shahab: none to declare