As e-cigarettes become more popular, there has been a push to understand whether they are a “gateway” to regular, combustible cigarettes.
As a public health professor with related research and interests in tobacco policy as well as in the complex factors that influence use of tobacco/nicotine products, I want to offer some thoughts on this research. Looking for a gateway effect between e-cigarettes and smoking is understandable. But is it the best question to ask about e-cigarette use?
These studies find evidence for a small association (or limited gateway) between e-cigarette use in nonsmokers and a progression to trying cigarettes in a one-year study period.
The more recent of the two studies was published in September 2015 (authored by Primack et al), in JAMA Pediatrics. Researchers followed 694 12-26-year-olds for a year. None had tried cigarette smoking at the study’s start, though 16 had tried e-cigarettes. (Perhaps the worthiest headline would be that only 2% of never-smokers tried e-cigarettes.)
A year later, 10% of the never-triers of e-cigarettes had taken at least one puff on a cigarette. But 38% (six of 16) of e-cigarette triers had taken at least one cigarette puff. This study focused on cigarettes and reports no information on prior hookah, cigar, marijuana, alcohol or smokeless tobacco use. If even two of the 16 were discounted because of prior use of other products, these results would likely be statistically insignificant.
The other study (authored by Leventhal et al) was published in August 2015 in JAMA. They followed 2,530 14-year-old school students for one year. None were smokers of any combustible tobacco products, including cigars, hookah and cigarettes at the start of the study, but 222 had tried e-cigarettes.
After 12 months, 25% of the e-cigarette triers had smoked at least one puff of a smoked tobacco product, compared to only 9% of the non-e-cigarette triers.
‘At least one puff’
Both studies found that young people who tried e-cigarettes were somewhat likelier to try smoked tobacco products, but that doesn’t mean e-cigarettes are a substantial gateway to regular smoking.
Rather than reporting usual measures of current smoking (ie, any cigarettes in the past 30 days) or daily smoking, both studies used “at least one puff” or “just a few puffs” in the past six months or lifetime.
It is as if an apple researcher thought “taking at least one bite of an apple in the past six months” was an important measure of initiation of apple eating.
But, research shows that a puff on one cigarette is crudely linked with daily smoking. Following teenagers who had not yet puffed on a cigarette, they found that 48% took at least one puff in the 12-month follow-up period. But of those, only 20% became daily smokers.
Leventhal et al do acknowledge that future work needs to assess risks of “regular, frequent” smoking. Indeed, until we understand if the observed small gateway is only to experimentation or to frequent, dependent smoking, the more critical question is unanswered. In that only a subset of these observed gateway triers will move on to be regular smokers, it is almost certain that further follow-up of these samples will be unable to demonstrate a major gateway to heavy tobacco use.
Both studies also used a measure of “susceptibility” to smoking that is even more tenuously connected to becoming a future frequent smoker and also can be greatly discounted by assessing prior use of other drug products, including smokeless tobacco.