Prior e-cigarette use was associated with a more than four-fold greater risk of ever smoking cigarettes and three-fold greater risk of current cigarette use in the prospective cohort study.
Findings from the nationally representative study, published online in JAMA Network Open, add to the growing evidence linking e-cigarette use to an increased risk for initiating cigarette smoking among youth, especially among low-risk teens.
Kaitlyn M. Berry, MPH, of Boston University School of Public Health, and colleagues, concluded that the findings highlight the need for “aggressive regulation” to restrict access to e-cigarettes among teens.
Several recent studies have raised the alarm about an elevated risk of smoking initiation among teen e-cigarette users, including a 2017 meta-analysis that found that teens and young adults who used e-cigarettes had more than three times the odds of later cigarette use and more than four times the odds of current cigarette smoking.
This analysis led the National Academies of Sciences to conclude in a 2018 report that there is “substantial evidence” that e-cigarette use increases the risk for cigarette-smoking tobacco-naive youth.
But in an email exchange with MedPage Today, Berry explained that many of the prior studies may have been subject to methodological limitations because they started with a sample of youth who were never cigarette users, assessed their e-cigarette use at that early time point, and then reviewed their smoking status after a year of follow-up.
“By removing cigarette users at the beginning, this design may overlook youth who started with e-cigarettes and already made the transition to cigarette smoking,” she said. “Additionally, the design may misclassify youth who started vaping between the two time points.”
The design of the new study, which centers around a youth’s very first tobacco product use, allowed the researchers to create what Berry described as “a loose timeline of the order of products used, that, in theory, avoids these potential issues.”
The researchers analyzed data from three waves of the nationally representative Population Assessment of Tobacco and Health (PATH) Study (2013-2016) in their effort to evaluate the association between prior e-cigarette use and use of other non-cigarette tobacco products with later cigarette initiation over a roughly 2-year period.
The sample included 6,123 respondents (49.5% female, 54.1% non-Hispanic white) with a mean age of 13.4 (1.2 years) who were tobacco-naive at baseline.
A total of 8.6% reported e-cigarettes as their first tobacco product, while 5.0% reported using another non-cigarette product first (3.3% reported using cigarettes first).
Cigarette use at wave 3 was higher among prior e-cigarette users (20.5%) compared with youths with no prior tobacco use (3.8%).
Among the other main findings:
- Prior e-cigarette use was associated with more than four times the odds of ever cigarette use (OR 4.09, 95% CI 2.97-5.63) and nearly three times the odds of current cigarette use (OR 2.75, 95% CI 1.60-4.73), compared with no prior tobacco use
- Prior use of other tobacco products was similarly associated with subsequent ever cigarette use (OR 3.84, 95% CI 2.63-5.63) and current cigarette use (OR 3.43, 95% CI 1.88-6.26), compared with no prior tobacco use
- At the population level, the analysis indicated that the fraction of ever cigarette use attributable to prior e-cigarette use was 21.8% (an estimated 178,850 youths) and 15.3% of current cigarette use (43,446 youths) among U.S. youths ages 12 to 15 may be attributable to prior e-cigarette use
Nine variables were used to categorize the respondents into risk groups, including alcohol, marijuana, and prescription drugs without a prescription. The association of prior e-cigarette use with cigarette initiation was found to be strongest among youth categorized as low-risk (OR 8.57, 95% CI 3.87-18.97).
The researchers concluded that this finding “raises concerns that e-cigarettes may re-normalize smoking behaviors and erode decades of progress in reducing smoking among youths.”