Big Question 7 - Are Smokeless Products a Gateway to Cigarette Smoking?

What does the Evidence on Gateway Effect Show Today?

With respect to the gateway effect, one review article reported that: “There was strong evidence for an association between e-cigarette use among non-smokers and later smoking (OR: 4.59, 95% CI: 3.60 to 5.85) when the results were meta-analysed in a random-effects model. However, there was high heterogeneity (I2=88%).” The authors further concluded: “However, the results do not provide strong evidence of a gateway effect”^[2].

An expert roundtable discussion funded by Cancer Research UK came to the following conclusion on the gateway effect: “The group felt that there was no convincing evidence in the UK to support the premise that e-cigarettes are acting as a gateway product in either adult or youth populations. Data have shown that only a small percentage of adult never smokers (0.3%) and youth never smokers (0.5%) are current daily vapers”^[3].

One delegate pointed out that if e-cigarettes were in fact a gateway product, one would surely see a rise in the overall population smoking rates since the introduction of e-cigarettes. However, many studies have shown the opposite to be true, with current smoking rates in England declining from 19.9% of adults over the age of 18 in 2010 to 15.5% in 2016^[3].

Furthermore, Cancer Research UK concluded: “And the good news is that smoking rates and the perceptions around the acceptability of smoking have declined in young people, even since the introduction of e-cigarettes. So, it doesn’t seem like e-cigarettes have interfered with the promising drop in levels of smoking in young people”^[4].

A recent analysis in Belgium of annual survey data showing an increase in e-cigarette use examined the relationship between vaping and smoking among Flemish youth^[5].

The survey data, collected by the Vlaams expertisecentrum Alcohol en andere Drugs (VAD) in 2021-2022, were analysed in collaboration with the Vlaams Instituut Gezond Leven.

The analysis reached the following main conclusions::

• Vaping among the underaged, who have never smoked is low, with 91.2% of those, who have never smoked, reporting that they also have never vaped;
• E-cigarette use among those who reported never smoking is typically temporary or occasional;
• Regular vaping is reported primarily by those who currently smoke or have smoked previously; and
• E-cigarette use among underage individuals is strongly linked to the smoking behaviour of their parents.

In a news release on the analysis, Vlaams Instituut Gezond Leven’s tobacco expert concluded that underaged vaping “is a nuanced story, in which two parameters are very important: the frequency of use and the link with (previous) smoking”^[6].

Recommendations for Future Study Design to Assess the Gateway Effect

• Usage classification should better reflect more representative real-world user behaviours (e.g. is a single puff in the past 30 days an appropriate basis for classifying an individual a smoker or a Vapour Product user?).
• Questionnaire data should be complemented by biochemical verification, with cotinine and N-(2 cyanoethyl)valine (CEVal) serving as useful markers of nicotine and cigarette use, respectively.
• Negative controls should be included to help determine whether observed associations are causal.
• Studies should collect detailed product information (e.g. nicotine strength and flavours used) to enable mechanisms underlying observed associations to be confirmed.