Powerful evidence that kids who use e-cigs more likely to start smoking cigarettes

On August 18, 2015, Adam Leventhal and his colleagues at USC published first longitudinal study of the relationship between e-cigarette use and starting to smoke cigarettes, “Association of Electronic Cigarette Use With Initiation of Combustible Tobacco Product Smoking in Early Adolescence” in JAMA.  This large, carefully done study followed 2530 9th graders for a year.  Never smoking youth who used e-cigarettes at baseline were 3-4 times more likely to be smoking cigarettes or other combustible tobacco products a year later.
 
This is a huge effect that is consistent with the earlier cross-sectional studies that suggested a “gateway effect” of e-cigarettes in promoting smoking of conventional cigarettes.
 
In addition, as the authors point out (and also consistent with earlier cross-sectional studies), there is also a reverse effect, with kids who start smoking more likely to use e-cigarettes.   But this paper demonstrates quite unequivocally that never smoking kids who use e-cigarettes are a lot more likely to become smokers.
 
It also blows away arguments that the results from our earlier cross-sectional study that showed strong linkages between e-cigarette use and progression to established smoking were the result of some sort of bizarre reverse causality.
 
This paper should force everyone to accept the reality that e-cigarettes are expanding and prolonging the tobacco epidemic, particularly since we know, from decades of tobacco control experience, that you can’t separate youth behavior from adults.
 
The FDA and other regulatory bodies need to act on that fact.  It also underscores the importance of including e-cigarettes in clean indoor air laws, voluntary smokefree home policies, and tobacco control media campaigns, including state and local campaigns (as San Francisco, Alaska, and California have done), including Legacy’s “truth” campaign.
 
Here is the abstract of the paper:
 

IMPORTANCE: Exposure to nicotine in electronic cigarettes (e-cigarettes) is becoming increasingly common among adolescents who report never having smoked combustible tobacco.
OBJECTIVE: To evaluate whether e-cigarette use among 14-year-old adolescents who have never tried combustible tobacco is associated with risk of initiating use of 3 combustible tobacco products (ie, cigarettes, cigars, and hookah).
DESIGN, SETTING, AND PARTICIPANTS: Longitudinal repeated assessment of a school-based cohort at baseline (fall 2013, 9th grade, mean age = 14.1 years) and at a 6-month follow-up (spring 2014, 9th grade) and a 12-month follow-up (fall 2014, 10th grade). Ten public high schools in Los Angeles, California, were recruited through convenience sampling. Participants were students who reported never using combustible tobacco at baseline and completed follow-up assessments at 6 or 12 months (N = 2530). At each time point, students completed self-report surveys during in-classroom data collections.
EXPOSURE: Student self-report of whether he or she ever used e-cigarettes (yes or no) at baseline.
MAIN OUTCOMES AND MEASURES: Six- and 12-month follow-up reports on use of any of the following tobacco products within the prior 6 months: (1) any combustible tobacco product (yes or no); (2) combustible cigarettes (yes or no), (3) cigars (yes or no); (4) hookah (yes or no); and (5) number of combustible tobacco products (range: 0-3).
RESULTS: Past 6-month use of any combustible tobacco product was more frequent in baseline e-cigarette ever users (n = 222) than never users (n = 2308) at the 6-month follow-up (30.7% vs 8.1%, respectively; difference between groups in prevalence rates, 22.7% [95% CI, 16.4%-28.9%]) and at the 12-month follow-up (25.2% vs 9.3%, respectively; difference between groups, 15.9% [95% CI, 10.0%-21.8%]). Baseline e-cigarette use was associated with greater likelihood of use of any combustible tobacco product averaged across the 2 follow-up periods in the unadjusted analyses (odds ratio [OR], 4.27 [95% CI, 3.19-5.71]) and in the analyses adjusted for sociodemographic, environmental, and intrapersonal risk factors for smoking (OR, 2.73 [95% CI, 2.00-3.73]). Product-specific analyses showed that baseline e-cigarette use was positively associated with combustible cigarette (OR, 2.65 [95% CI, 1.73-4.05]), cigar (OR, 4.85 [95% CI, 3.38-6.96]), and hookah (OR, 3.25 [95% CI, 2.29-4.62]) use and with the number of different combustible products used (OR, 4.26 [95% CI, 3.16-5.74]) averaged across the 2 follow-up periods.
CONCLUSIONS AND RELEVANCE: Among high school students in Los Angeles, those who had ever used e-cigarettes at baseline compared with nonusers were more likely to report initiation of combustible tobacco use over the next year. Further research is needed to understand whether this association may be causal.

 
The full paper is available here; and excellent accompanying commentary by Harvard’s Nancy Rigotti is here.