Commentary on Beard et al.: Using survey data to test the hypothesis that e-cigarettes are a gateway to cigarette smoking in youth.

Beard and colleagues’ analyses of survey data in England, and similar studies in the United States, strongly suggest that any gateway effects of e‐cigarettes are far smaller than those reported in cohort studies and are insufficient to justify bans on the sales of e‐cigarettes to adult smokers.

The claim that e‐cigarettes are a gateway to tobacco cigarette smoking in youth has been used as a major justification for restricting the sales of nicotine e‐cigarettes in Australia [1, 2]. Cohort studies have been interpreted as evidence that youth and young adults who use e‐cigarettes are more likely to smoke cigarettes [2]. However, these studies often suffer from major methodological weaknesses; namely, high rates of sample attrition and inadequate adjustment for potential confounders, which may overestimate the association between e‐cigarette use and smoking initiation [3]. Further, a substantial proportion of this association between e‐cigarette use and tobacco smoking may be explained by shared common risk factors, such as a genetic vulnerability to nicotine dependence, parental smoking and adolescent risk‐taking [3].

The critical question in assessing the gateway hypothesis at the population level, is: ‘Has increased uptake of e‐cigarettes among youth been followed by an increase in their tobacco cigarette smoking?’

Beard and colleagues [4] answer this question by analyzing extensive time–series data between 2007 and 2018 on trends in e‐cigarette uptake and cigarette smoking among youth and young adults in England; a country which has facilitated access to e‐cigarettes so that adult smokers can use them for cessation or harm reduction. The authors find no association between increases in e‐cigarette use and cigarette smoking in youth and young adults aged 16–24 years (and separately among those aged 16–17 and 18–24 years). They estimate that the number of additional smokers who may have been recruited via e‐cigarettes is greatly outnumbered by the much larger number of smokers who quit smoking using e‐cigarettes. The authors acknowledged that they could not rule out a small gateway effect of e‐cigarettes on cigarette smoking, but showed that their study had sufficient statistical power to be confident that youth e‐cigarette use has not been associated with substantial increases or decreases in the prevalence of smoking among young people.

Beard et al.’s findings in England are supported by analyses of population‐level data on trends in e‐cigarette use and cigarette smoking in the United States [5, 6]. The United States provides an interesting test case because both the National Youth Tobacco Survey and the Monitoring the Future study showed a dramatic increase in e‐cigarette use among youth, thanks to lax regulations of e‐cigarette sales and marketing. Despite the increase in e‐cigarette use, cigarette smoking decreased from 11.3 to 3.7% among youth who did not use e‐cigarettes between 2014 and 2019 and from 28.4 to 9.9% in youth who used e‐cigarettes regularly.

Population‐level data on young people’s future intentions to smoke cigarettes and the perceived risks of cigarette smoking among young people who use e‐cigarettes also provide little support for the gateway hypothesis. Future intentions to smoke cigarettes have decreased and the proportion of young people who perceived cigarette smoking to be harmless has remained low. They did not change in users or non‐users of e‐cigarettes between 2014 to 2018 [5]. The decreased prevalence of cigarette smoking, intention to smoke and the lack of change in the perceived harms of cigarette smoking are not consistent with e‐cigarettes serving as a gateway to cigarette smoking. They are more consistent with the displacement hypothesis that the introduction of e‐cigarettes has decreased the prevalence of cigarette smoking among youth by diverting them from cigarettes towards less harmful e‐cigarettes [6, 7].

The analyses of Beard and colleagues, and the literature more broadly, strongly suggest that any gateway effects of e‐cigarettes are far smaller than that those reported in cohort studies. This evidence undermines the use of the gateway hypothesis to justify bans on the sale of e‐cigarettes to adult smokers while cigarette smoking remains a leading global cause of preventable disease and death. E‐cigarettes can offer a viable form of harm reduction for adult smokers because they have considerably lower levels of carcinogens than combustible cigarettes and are effective for quitting cigarette smoking [8].

We should reduce e‐cigarette use among youth even if this does not increase cigarette smoking. We can minimize e‐cigarette uptake among non‐smoking youth (without restricting smokers’ access) by enforcing age restrictions on e‐cigarette purchases and limiting the number and density of licensed e‐cigarette sales outlets. We should also ban the advertising and promotion of e‐cigarettes, except at point of sale, for any purpose other than assisting smokers to quit or reduce the harms of cigarette smoking.

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