e-Cigarette Use and Subsequent Tobacco Use by Adolescents: New Evidence About a Potential Risk of e-Cigarettes.

Few topics in public health and medicine are as contentious as electronic cigarettes (e-cigarettes), novel handheld battery-operated nicotine-delivery devices that resemble conventional tobacco cigarettes and simulate the experience of smoking a cigarette.1-3 Unlike cigarettes that burn tobacco to generate smoke, e-cigarettes heat a liquid consisting of nicotine, propylene glycol or glycerin, flavorings, and other chemicals to create a vapor that is inhaled. Both conventional cigarettes and e-cigarettes deliver nicotine, the addictive agent in tobacco, but e-cigarettes do not expose the user to the many other tobacco smoke constituents responsible for causing tobacco-related diseases. e-Cigarettes therefore offer the tantalizing prospect that they could reduce the harms of conventional tobacco use, the leading cause of preventable death and disability in the United States and worldwide.4 e-Cigarettes have substantial consumer appeal, generating an estimated $2.2 billion in revenue in the United States in 2014.5 Their use by adults and adolescents in the United States has increased substantially.6,7 Their novel design and consumerappealmakee-cigarettesa“disruptive technology,”3 andtheirpotentialbenefitsandharmsaresubstantial andhotly debated.1,2 Meanwhile, the characteristics of these products are evolving; newer generationsdelivermorenicotine and resemble cigarettes less.8 Thus, e-cigarettes raise many questions forwhich thereare fewanswers.Theevidencebase is limited because e-cigarettes entered the marketplace without being regulated as either drugs or devices. The primary potential benefit of e-cigarettes is to reduce the prevalence of tobacco use by helping current smokers to quit or to switch completely and permanently from combustible tobacco to e-cigarette use. Dual use involving substituting someconventional cigaretteswith e-cigaretteswouldprovide far lessbenefit.However, anybenefitofe-cigaretteswould be offset to the extent that these products are harmful. The 3 principal public health concerns about e-cigarettes are their potential to renormalize cigarette use if they are permitted in venueswhere cigarettes are banned; their potential appeal to nonsmokers, especially to children and adolescents; and their possible health risks as a result of users’ exposure to e-cigarette constituents, such as flavorings or propylene glycol, or to e-cigarette contaminants.9 e-Cigarettes could increase tobacco use initiation rates if youthswhowouldnothaveotherwise triedconventional cigarettes try e-cigarettes, becomeaddicted tonicotine, and transition tousingcombustible tobaccoproducts.Adolescentsmay be especially susceptible to develop nicotine addiction after e-cigarette exposure because their brains are still developing and are particularly sensitive to nicotine.4 There is universal agreement that this is not a good outcome, and there is concern that it could occur because e-cigarettes are marketed in ways that appeal to youth.8 Whetheradolescents’useofe-cigarettespredisposes them to initiate conventional tobacco use is a critical question for assessing the net public health effect of e-cigarettes. The existing evidence derives from cross-sectional studies. In a nationally representative sample of US middle and high school students from 2011-2013, ever use of e-cigarettes was associated with conventional tobacco product use and with a measure of susceptibility to start smoking in the future,10 consistentwith anearlier analysis.11 In anational surveyofUSyoung adults from 2012-2013, ever use of e-cigarettes was associatedwithanopenness to smokeconventional cigarettes.12 The associations observed in these studies persisted after statistical adjustment for potential confounders, but crosssectional studydesigns cannot establish causality or the temporal direction of observed relationships.13 A longitudinal study can help untangle the temporality of these relationships. In this issue of JAMA, Leventhal and colleagues14 report findings fromsuchastudy.Theauthorsused a repeated-measuresprospectiveobservational studydesign to assess combustible tobacco and e-cigarette use among a diverse cohort of 2530 ninth graders attending 10 public high schools in Los Angeles, California, from 2013-2014.14 At baseline, all students were nonsmokers (defined has never having used a combustible tobacco product, including cigarettes, cigars, blunts, and hookah); 222 (8.8%) of them had ever used an e-cigarette. Nonsmokers with previous exposure to e-cigarettes at initial interview compared with those without exposure toe-cigarettesweremore likely to reportuseofacombustible tobacco product during the next 6 months (30.7% vs 8.1%, respectively) and 12 months (25.2% vs 9.3%, respectively). Significant associations also were found for each individual tobacco product, including cigarettes, cigars, and hookah. The investigators carefully adjusted the analysis for manyknownsociodemographic, family,environmental,andintrapersonal factors associated with e-cigarette and combustible tobacco use. This adjustment substantially lowered the magnitude of the association between e-cigarettes and subsequent tobaccouse (odds ratio [OR]declined from4.27 [95%CI, 3.19-5.71] to 2.73 [95%CI, 2.00-3.73]), suggesting that these facAuthor Audio Interview at jama.com