Teens who use e-cigarettes are more likely to smoke tobacco cigarettes later on—but the opposite wasn’t true, found a new long-term study that surveyed high school students over three years. That is, teens who smoked tobacco cigarettes were not more likely to later use e-cigarettes, or “vape.”
“With this study, we add longitudinal, causal evidence that the transition from e-cigarettes to combustible products, at least for adolescents, is a one-way street,” wrote Jonathan Klein, MD, from the University of Illinois Pediatrics Department in Chicago, in an accompanying editorial.
E-cigarettes are currently the most popular nicotine- or tobacco-related product among youth, with an estimated 3 million teens vaping, according to lead author Krysten W. Bold, PhD, of the Department of Psychiatry at Yale University School of Medicine, and her colleagues, in their study’s background information.
“The rising frequency of recent e-cigarette use among youth over time is concerning, especially in light of evidence that e-cigarette use is a significant risk factor for future conventional cigarette use,” the authors wrote. The study, funded by the National Institutes of Health, was published in the journal Pediatrics.
Multiple studies have looked at whether teens go on to smoke tobacco cigarettes after trying e-cigarettes, but findings haven’t always been consistent, largely due to differences in study designs.
One of the biggest, and most legitimate, criticisms of this research is the unreliability of cross-sectional studies, in which researchers ask teens at only one point in time about their use of e-cigarettes and tobacco cigarettes. These studies can’t offer much information on which came first.
Long-term (longitudinal) studies offer more insight into what teens try and when, and many of these show a higher risk of tobacco cigarette use after e-cigarettes use, even after accounting for other demographic, social and behavioral factors that may influence teens’ risk of smoking. But most of these are still limited when they only compare two different points in time instead of looking at trends over several points in time.
In this study, researchers surveyed 1,408 Connecticut high school students three times, in autumn 2013, spring 2014 and autumn 2015, about their use of e-cigarettes and traditional tobacco cigarettes within the past month.
As other studies have done, the researchers adjusted their calculations to account for differences among the students’ sex, race/ethnicity, socioeconomic status and use of other tobacco products, such as smokeless tobacco, cigars, hookah and blunts.
The surveys were anonymous to encourage greater honesty from the students, and researchers matched each year’s survey using unique ID codes. The researchers matched 1,098 students from 2013 to 2014 and 972 students from 2014 to 2015. The scientists only analyzed findings from the 808 students they could match across all three years.
Teens answered the following exact questions at each survey:
- “Have you ever tried an e-cigarette?” (yes or no)
- “How many days out of the past 30 days did you use e-cigarettes?” (0–30, open-ended response)
- “Have you ever tried a cigarette, even just 1 or 2 puffs?” (yes or no)
- “During the past 30 days, on how many days did you smoke a cigarette (even just 1 or 2 puffs)?” (“none,” “1 day,” “2 days,” “3 to 5 days,” “6 to 10 days,” “11 to 20 days”)
Unsurprisingly, teens who reported smoking cigarettes at the first survey were more likely to report smoking during the second and third surveys, and the same was true for e-cigarettes.
But the researchers found that only e-cigarette users were more likely to later smoke tobacco cigarettes, not vice versa. Teens who used an e-cigarette within the past month in 2013 had 7 times greater odds of smoking tobacco cigarettes in 2014. A year later, e-cigarette users were more than 3 times more likely to smoke tobacco cigarettes.
Meanwhile, teens who reporting smoking tobacco cigarettes in 2013 or 2014 were no more likely to use e-cigarettes over the next two years than those who didn’t smoke any cigarettes.
Overall use of both product types also increased over time: cigarette use within the past month increased from 4.8% of students in 2013 to 8.5% in the third year. Similarly, e-cigarette use began at 8.9% in 2013 and increased to 14.5%. By 2015, just over a quarter of cigarette smokers (26%) and one in five e-cigarette users (20.5%) were using cigarettes 21-30 days out of the past month.
The authors recommend that more research investigate what might explain the increased risk of smoking among teens who use e-cigarettes when the opposite doesn’t occur.
“For example, adolescents may be more likely to use e-cigarettes before conventional cigarettes because of factors unique to e-cigarette products, such as perceptions that e-cigarettes are less harmful than conventional cigarettes, the widespread availability of unique e-cigarette liquid flavors that may be especially appealing to youth and limited enforcement or restrictions on youth access to e-cigarettes,” such as online sales, the authors wrote.
“At the same time, there is evidence that the adolescent brain is highly sensitive to the rewarding effects of nicotine, so e-cigarette use may provide early exposure to the reinforcing pharmacological effects of nicotine, which may increase the likelihood of transitioning to conventional cigarettes,” they speculated.
They also suggested that teens may be able to get more nicotine through traditional cigarettes than through e-cigarettes over time, depending on the e-cigarette device, “so youth who use conventional cigarettes may find e-cigarettes less reinforcing and be less likely to transition in the reverse direction: from cigarette to e-cigarette use over time.”
Because this study is observational, it’s not possible to determine cause and effect or answer why tobacco cigarette use increases among e-cigarette users without the opposite being true. The study is also limited by having mostly white participants, which may not apply to more diverse demographics. The authors also did not collect information on parents’ tobacco use, exposure to cigarette advertising or specifics on the products used by teens beyond the type.
The study’s findings call into question claims from some harm reduction e-cigarette advocates that teens may be likely to use e-cigarettes to quit smoking, suggested Klein.
“E-cigarette products were not part of young people’s efforts to quit,” Klein wrote. “E-cigarettes cause combustible smoking; they lead young people to cigarette use and nicotine addiction.”
He noted findings from animal research that e-cigarette vapor can harm growing lungs and that it produces “immediate and harmful effects on both immune and arterial function, contributing to infectious diseases, heart disease and triggering heart attacks.”
Klein called for preventing teens from any initial exposure to nicotine, from any product, and cited research that e-cigarette flavors increase teens’ likelihood of using them. Conversely, removing flavors reduces teens’ use.