E-Cigarettes and the Use of Conventional Cigarettes
A cohort study in 10th grade students in Germany
; ; ;
Background: In 2015, 12.1% of 12– to 17-year-olds in Germany had reportedly already tried e-cigarette smoking at least once. We carried out a study of the “gateway” hypothesis, according to which the use of e-cigarettes can motivate adolescents to start smoking conventional cigarettes.
Methods: During the 2015/2016 school year, 2186 tenth-graders in the German states of Lower Saxony and Schleswig-Holstein who had never smoked conventional cigarettes before took part in a survey over a 6-month period (mean age 15.5 years, standard deviation 0.65; 53.6% female).
Results: 14.3% of the survey population (313 adolescents) said at the start of the survey period that they had already tried e-cigarettes at least once. By the end of the survey period, 12.3% (268) of those who had never smoked before had begun to experiment with conventional cigarettes. The risk of beginning such experimentation was 2.2 times higher among e-cigarette users. This association remained (relative risk = 2.18 [1.65; 2.83]) after statistical control for age, sex, state, immigrant background, type of school, socioeconomic status, various personality traits (sensation-seeking, impulsivity, anxiety, hopelessness, extraversion, agreeableness, conscientiousness, neuroticism, openness), and the use of alcohol, cannabis, and other illicit drugs. Further analysis revealed that the association between the use of e-cigarettes and the onset of conventional cigarette smoking was stronger among adolescents with low sensation-seeking scores and without any experience of alcohol intoxication.
Conclusion: Among adolescents who have never smoked, experimentation with conventional cigarettes is more common in those who have used e-cigarettes. This effect seems to be stronger among adolescents who, in general, have a lower risk of starting to smoke. The 6-month observation period of this study is too short to allow any inference regarding a connection between e-cigarette use and the development of tobacco dependence.
Electronic cigarettes, or e-cigarettes, are battery-powered electronic devices, releasing aerosolized nicotine without combustion processes for inhalation (1). For about a decade, e-cigarettes have been freely available to consumers. Initially, e-cigarettes were sold online, later also in specialist stores. Today, a wide variety of products is on the market, including e-hookahs, a variant of e-cigarette frequently printed in bright colors and often looking like colored markers, potentially making them particularly attractive to children and adolescents.
The number of regular e-cigarette users in Germany has increased dramatically in recent years. A representative population-based cross-sectional survey of 4002 randomly selected individuals aged 14 and older conducted in 2016 found that 1 in 8 Germans had already tried e-cigarettes at least once and that experimental use of e-cigarettes among non-smokers appeared to be more widespread in adolescents than in other age groups (2).
For more than a decade, the use of conventional cigarettes has been declining among adolescents (3). While 27.5% of the 12– to 17-year-olds at least occasionally smoked conventional cigarettes in 2001, this only applied to 7.8% of persons in this age group in 2015 (4). In Germany, the proportion of children and adolescents with experience in the use of e-cigarettes and e-hookahs is substantial: In 2015, 12.1% and 13.5% of the 12– to 17-year-olds in Germany had at least once tried e-cigarettes and e-hookahs, respectively (4). In the group of 12– to 13-year-olds, experiences with the consumption of e-cigarettes may be more common than with the use of conventional cigarettes (5).
There is ongoing debate about the benefits and harms of e-cigarettes in the medical research community. Various aspects are being discussed which must be balanced according to their importance (6). Studies about long-term health effects are needed (7). In addition, the question arises as to whether there is a health risk associated with passive exposure to e-cigarette vapor, similar to the risk of passive smoking associated with conventional cigarettes (8). Furthermore, high hopes are being entertained as to the use of e-cigarettes for smoking cessation, but the data obtained so far have been very heterogeneous (9–13). Another argument is that e-cigarettes may promote the renormalization of smoking of conventional cigarettes in society (14).
In the mid 1970s, the gateway hypothesis was developed by Denise Kandel (15). Kandel observed that the sequence of initial consumption of various drugs did not vary randomly, but showed systematic trends—for example, that the consumption of nicotine and alcohol precedes the use of illegal substances, such as cannabis or cocaine. The gateway hypothesis was strongly criticized from various sides (16), the main concern being the lack of a causal explanation. In Germany, for example, only a small proportion of the population consumes cocaine or other hard drugs despite the widespread consumption of alcohol in the population.
More recently, Eric Kandel and Denise Kandel have conducted experiments with mice to obtain data supporting the potential role of nicotine as a gateway drug (17). Their experiments showed that after prior administration of nicotine, administration of cocaine had different effects on the mouse organism, e.g. an increased striatal acetylation. This observation gave rise to concerns that the use of nicotine-containing liquids in e-cigarettes could be a gateway to the use of conventional cigarettes (16–19).
Schneider and Diehl discussed 3 potential mechanisms for the transition from e-cigarettes to conventional cigarettes (16):
- Addiction: Although the potential of e-cigarettes to cause physical and psychological dependence is not yet clearly understood, it is conceivable that tolerance development in adolescents used to nicotine consumption is responsible for transition to conventional cigarettes, driven by the urge to increase nicotine doses.
- Experience: The familiarity with habitual and ritual processes (smoking breaks, hand position, topography, etc.) resulting from regular e-cigarette consumption could promote subsequent transition to conventional cigarettes.
- Accessibility: E-cigarettes and tobacco cigarettes are typically offered via the same sales channels (tobacco shops, kiosks, gas stations).
One of the first studies to test this hypothesis evaluated a cohort of 694 adolescents and young adults (20). At baseline, only 16 of these reported experiences with e-cigarettes. Compared to adolescents without e-cigarette consumption experience, these had an 8-fold increase in the risk of smoking conventional cigarettes for the first time in their life during the 1-year follow-up period. In the meantime, additional cohort studies have been published (21). These studies were conducted in Anglo-America (22–33), the United Kingdom (34, 35) and Mexico (36). Overall, their results indicate that the initial use of e-cigarettes during adolescence may be associated with an increased risk for initiation of conventional cigarette use.
We are not aware of any longitudinal studies on cohorts in Germany on the topic of e-cigarettes. A recent review rated the methodological quality of the international studies published so far as moderate (37). Major limitations criticized were the limited number of confounding variables measured and the very high attrition rate during the follow-up period which in some studies was as high as half of the surveyed adolescents.
The aim of this study was to evaluate whether e-cigarette use in adolescence can increase the risk of conventional cigarette use. An additional question to be addressed was whether the use of e-cigarettes just represents a criterion which identifies adolescents who in any case are at increased risk of starting to smoke. For this end, we were the first to collect data on personality traits of the adolescents surveyed.
Altogether, 4163 10th grade students were surveyed at baseline (2015/2016 school year; response rate of 84.5%), with 2358 (57.1%) of these students reporting that they had never tried conventional cigarettes at any time in their life. Of these, 2186 students could be successfully contacted again half a year later (re-contact rate of 92.7%). Further characteristics of this study are described in the eBoxes 1 to 3.
For statistical analysis, a multiple regression model was used which included all variables, i.e. sociodemographic and personality variables as well as consumption of other substances. In a further step of the analysis, interaction terms were used to test whether the various model variables had an impact on the association between e-cigarette consumption and the use of conventional cigarettes. For further information about the statistical analysis, please refer to eBox 4.
Sample description and attrition analysis
Table 1 lists the characteristics of the sample, both for the entire study population at baseline and the sample included in the analysis (mean age: 15.5 years; 53.6% female). In addition, a comparison between former never-smoking students who could be successfully contacted and those who could not be contacted shows the extent of selective attrition of participants. More frequently, it was possible to successfully contact never-smokers who were younger, were surveyed in the federal state of Schleswig-Holstein, had no migration background, had lower scores on the personality traits sensation seeking, impulsivity, hopelessness, and extraversion, and had less often consumed e-cigarettes, cannabis and other illegal drugs.
Association between the variables studied and initiation of smoking conventional cigarettes
During the follow-up period, 268 of the 2186 formerly never-smoking adolescents (12.3%) smoked conventional cigarettes for the first time in their life. In the unadjusted model (model 1), the frequency of conventional cigarette consumption was significantly associated with gender (more rarely among female students), type of school (more rarely among upper high school students) and the personality traits sensation seeking, impulsivity, anxiety sensitivity, extraversion, and neuroticism (eTable 1). In addition, smoking initiation was more frequently observed among those students who had already had experiences with alcohol, binge drinking, cannabis, and e-cigarettes. In the multiple regression model, 6 variables were identified as independent predictors (Table 2):
- Type of school
- Migration background
- The personality traits sensation seeking and hopelessness
- Binge drinking
- E-cigarette consumption at baseline.
Experimental use of conventional cigarettes was at 21.6% in the group of e-cigarette consumers, while it was at 9.9% in the group of students without experience with e-cigarettes (risk ratio = 2.18).
Testing for interaction effects found significant effect modifications related to sensation seeking (risk ratio [RR] = 0.48, 95% confidence interval [CI]: [0.29; 0.82]) and experience with binge drinking (RR = 0.47, 95% confidence interval: [0.27; 0.83]). As shown in the Figure, the connection between the use of e-cigarettes and smoking initiation was stronger in persons with low scores in sensation seeking compared to students scoring high in sensation seeking. In the same way, the association was stronger for students without binge drinking experience compared to students with binge drinking experience.
A cohort of 2186 10th grade students who had never smoked conventional cigarettes in their life were observed over a half-year period. An association between experiences with the consumption of e-cigarettes at baseline and the experimental use of conventional cigarettes during the follow-up period was demonstrated and still present after adjustment for numerous confounding variables.
With regard to the association between consumption of e-cigarettes and initiation of conventional cigarette use, the results obtained in this study were comparable to those of studies on US cohorts. A recent meta-analysis of 7 cohort studies reported an adjusted odds ratio of 3.62 [2.42; 5.41] for adolescents and young adults with experience in e-cigarettes consumption at baseline compared to persons without consumption experience (37). The risk ratio of 2.2 in the current German cohort corresponds to an adjusted odds ratio of 2.8; here, it has to be taken into account that considerable more confounding variables were controlled in this study compared to the 7 cohort studies included in the meta-analysis.
The personality trait “sensation seeking” is defined by the search for changing and novel experiences to feel intense sensations again and again. Sensation seeking is a construct with a physiological basis, assuming that for every individual there is an optimal arousal (38). By seeking or avoiding stimulation, arousal can be controlled on an individual level. In line with other studies, our study showed that risk-taking behavior—here the experimental use of conventional cigarettes—can be predicted based on this personality trait. However, here the more pressing question is whether the use of e-cigarettes is not merely an indication that theses persons in general seek stimulations and whether this explains why they start smoking earlier. Our study did not only show that the correlation between sensation seeking and e-cigarette use in the group of never-smoking adolescents is rather weak (correlation coefficient: r = 0.11) (eTable 2), but also that in particular those students with low sensation seeking—i.e. persons with a tendency to avoid risky behavior—were encouraged by the use of e-cigarettes to try conventional cigarettes too.
In Germany, tobacco smoking among adolescents does not occur independently of the type of school attended (39). This finding was also confirmed in our analysis: In German upper secondary schools (“Gymnasium”), smoking was less common and less students started experimenting with smoking during the follow-up period. However, the association between use of e-cigarettes and initiation of smoking was almost equally strong in upper secondary school students and non-upper secondary school students and thus can be regarded as independent of school type.
However clear these current findings may appear, the interpretation of these data should take some limitations into account. For ethical reasons, the gateway hypothesis cannot be studied using an experimental model. In general, observational studies are more prone to systematic biases compared to randomized clinical trials and they do not allow us to establish causality (40). For example, when interpreting the results it should be taken into consideration that external validity can be affected by selection bias and internal validity by unmeasured confounding. Selection bias can occur when the study population is not randomly selected from the target population; this is the case in our study. Despite the large number of variables measured in this study, confounding of the association by one or more third variables can never be ruled out completely. Especially the impact of the immediate social environment—for example, smoking friends or smoking parents—was not adequately accounted for. Likewise, it cannot be ruled out with certainty that users of e-cigarettes had not started smoking anyway at a later point in time.
As a further limitation, the question should be discussed whether the result “ever smoked” is a clinical or health-relevant parameter at all. Even though it is well established that nicotine has a very high addictive potential, single experimental use among adolescents does not necessarily result in dependence (e1). In our data set, 83 persons changed from non-daily to daily tobacco consumption during the 6-month follow-up period. This transition, too, was associated with prior e-cigarette use (eTable 3).
It must be emphasized that, mainly due to the short duration of its follow-up period, this study does not allow any conclusions to be drawn about the long-term impact of the use of e-cigarettes on the development of tobacco dependence.
The method of data collection represents another limitation of this study, as it was not based on objective measurements and could be affected by systematic response bias. Multiple testing of the same sample carries the risk of alpha-error inflation; this limitation should also be kept in mind when interpreting the results. Furthermore, no data were collected on the type of liquids—with or without nicotine—consumed by the adolescents. Based on existing surveys from Germany, it can be assumed that nicotine-containing liquids are used by about one third of the e-cigarettes–consuming adolescents (2, 4, e2). Addiction, in the sense of physical and psychological dependence, as the mechanism underlying the transition to tobacco smoking as postulated by Schneider and Diehl (16), can essentially only be applied to adolescents who are exposed to nicotine when using e-cigarettes. The same applies to the experience hypothesis, i.e. the familiarity with habitual and ritual processes resulting from regular e-cigarettes consumption, which cannot be tested using data on experimental consumption.
In Germany, the sale of e-cigarettes and e-hookahs to children and adolescents was prohibited not earlier than 1 April 2016. Thus, during the follow-up period of this study, adolescents could legally purchase e-cigarettes. It cannot be ruled out that this change will have an impact on the prevalence of e-cigarette use among adolescents. However, as it can be learned from the prevalences of tobacco and alcohol consumption, the legal age to buy such products is not a key determinant of the initiation of consumption.
This study supports the ongoing discussion of potential benefits and harms of e-cigarettes by reporting empirical data. The association between e-cigarette consumption and the use of conventional cigarettes, which to date had only been shown for Anglo-American, British and Mexican samples, was also demonstrated for a cohort of adolescents in Germany. This result—which at least is not contradictory to the gateway hypothesis—should be taken into account when balancing advantages and disadvantages of e-cigarettes.
In the United States, smoking behavior among adolescents has changed significantly in recent years: The use of conventional cigarettes alone has declined, while the consumption of e-cigarettes has increased and a likewise considerable proportion of adolescents consumes both products in parallel and uses other tobacco products, such as hookahs, too (e3, e4). Whether these trends will also occur in Germany, should be carefully monitored.
We would like to thank Toska Jakob, Corinna Köhler, Luise Rehermann, Milene Wiehl, Jörn Frischemeier, Markus Watermeyer, Hanife Özbek, Melanie Maida, Myriam Lemberger, Sarah C. Murray, and Lena Heister for their support with data collection. We would also like to thank all schools, teachers and students for their collaboration.
This study was funded by the Federal Center for Health Education on behalf of the Federal Ministry for Health.
Conflict of interest
The authors declare no conflict of interest.
Manuscript received on: 2 November 2017; revised version accepted on 23 January 2018
Translated from the original German by Ralf Thoene, M.D.
Prof. Dr. phil. Reiner Hanewinkel
Institut für Therapie- und Gesundheitsforschung
IFT-Nord gGmbH, Harmsstr. 2
PD Dr. phil. Matthis Morgenstern, Alina Nies, Prof. Dr. phil. Reiner Hanewinkel
Federal Center for Health Education, Cologne, Germany: Michaela Goecke, MA
|1.||Nowak D, Jorres RA, Rüther T: E-cigarettes—prevention, pulmonary health, and addiction. Dtsch Arztebl Int 2014; 111: 349–55 VOLLTEXT|
|2.||Eichler M, Blettner M, Singer S: The use of e-cigarettes. Dtsch Arztebl Int 2016; 113: 847–54 VOLLTEXT|
|3.||Kuntz B, Lampert T: Smoking and passive smoke exposure among adolescents in Germany. Dtsch Arztebl Int 2016; 113: 23–30 VOLLTEXT|
|4.||Orth B: Die Drogenaffinität Jugendlicher in der Bundesrepublik Deutschland 2015: Rauchen, Alkoholkonsum und Konsum illegaler Drogen: aktuelle Verbreitung und Trends. Köln: Bundeszentrale für gesundheitliche Aufklärung 2016.|
|5.||Schneider S, Görig T, Herr R, et al.: Die E-Zigarette – Verbreitung, Konsummuster und Nutzermotive bei Siebt- und Achtklässlern. Sucht 2016; 62: 153–62 CrossRef|
|6.||Schaller K, Mons U: E-Shishas und E-Zigaretten: Debatte um Schaden und Nutzen. Dtsch Arztbl 2017; 114: A 70–1.|
|7.||Pisinger C, Dossing M: A systematic review of health effects of electronic cigarettes. Prev Med 2014; 69: 248–60 CrossRef MEDLINE|
|8.||Hess IM, Lachireddy K, Capon A: A systematic review of the health risks from passive exposure to electronic cigarette vapour. Public Health Res Pract 2016; 26: e2621617 CrossRef MEDLINE|
|9.||Kalkhoran S, Glantz SA: E-cigarettes and smoking cessation in real-world and clinical settings: a systematic review and meta-analysis. Lancet Respir Med 2016; 4: 116–28 CrossRef|
|10.||Khoudigian S, Devji T, Lytvyn L, Campbell K, Hopkins R, O‘Reilly D: The efficacy and short-term effects of electronic cigarettes as a method for smoking cessation: a systematic review and a meta-analysis. Int J Public Health 2016; 61: 257–67 CrossRef MEDLINE|
|11.||Zhu SH, Zhuang YL, Wong S, Cummins SE, Tedeschi GJ: E-cigarette use and associated changes in population smoking cessation: evidence from US current population surveys. BMJ 2017; 358: j3262 CrossRef MEDLINE PubMed Central|
|12.||Gmel G, Baggio S, Mohler-Kuo M, Daeppen JB, Studer J: E-cigarette use in young Swiss men: is vaping an effective way of reducing or quitting smoking? Swiss Med Wkly 2016; 146: w14271 CrossRef|
|13.||Kröger CB, Ofner S, Piontek D: Nutzung und Nutzen der E-Zigarette im Rahmen eines strukturierten verhaltenstherapeutischen Gruppenprogramms: Ergebnisse einer 12-Monats-Nachbefragung. Bundesgesundheitsblatt Gesundheitsforschung Gesundheitsschutz 2018; 61: 32–9 CrossRef MEDLINE|
|14.||Fairchild AL, Bayer R, Colgrove J: The renormalization of smoking? E-cigarettes and the tobacco „endgame“. N Engl J Med 2014; 370: 293–5 CrossRef MEDLINE|
|15.||Kandel DB: Stages in adolescent involvement in drug use. Science 1975; 190: 912–4 CrossRef|
|16.||Schneider S, Diehl K: Vaping as a catalyst for smoking? An initial model on the initiation of electronic cigarette use and the transition to tobacco smoking among adolescents. Nicotine Tob Res 2016; 18: 647–53 CrossRef MEDLINE|
|17.||Kandel ER, Kandel DB: Shattuck lecture. A molecular basis for nicotine as a gateway drug. N Engl J Med 2014; 371: 932–43 CrossRef MEDLINE PubMed Central|
|18.||Etter JF: Gateway effects and electronic cigarettes. Addiction 2017: Epub ahead of print CrossRef MEDLINE|
|19.||Gartner C: E-cigarettes and youth smoking: be alert but not alarmed. Tob Control 2017; Epub ahead of print CrossRef|
|20.||Primack BA, Soneji S, Stoolmiller M, Fine MJ, Sargent JD: Progression to traditional cigarette smoking after electronic cigarette use among US adolescents and young adults. JAMA Pediatr 2015; 169: 1018–23 CrossRef MEDLINE PubMed Central|
|21.||Chatterjee K, Alzghoul B, Innabi A, Meena N: Is vaping a gateway to smoking: a review of the longitudinal studies. Int J Adolesc Med Health 2016; Epub ahead of print CrossRef MEDLINE|
|22.||Barrington-Trimis JL, Urman R, Berhane K, et al.: E-cigarettes and future cigarette use. Pediatrics 2016; 138: e20153983 CrossRef CrossRef|
|23.||Leventhal AM, Strong DR, Kirkpatrick MG, et al.: Association of electronic cigarette use with initiation of combustible tobacco product smoking in early adolescence. JAMA 2015; 314: 700–7 CrossRef MEDLINE PubMed Central|
|24.||Loukas A, Marti CN, Cooper M, Pasch KE, Perry CL: Exclusive e-cigarette use predicts cigarette initiation among college students. Addict Behav 2017; 76: 343–7 CrossRef MEDLINE|
|25.||Miech R, Patrick ME, O‘Malley PM, Johnston LD: E-cigarette use as a predictor of cigarette smoking: results from a 1-year follow-up of a national sample of 12th grade students. Tob Control 2017; 26: e106–11 CrossRef MEDLINE|
|26.||Spindle TR, Hiler MM, Cooke ME, Eissenberg T, Kendler KS, Dick DM: Electronic cigarette use and uptake of cigarette smoking: a longitudinal examination of U.S. college students. Addict Behav 2017; 67: 66–72 CrossRef MEDLINE PubMed Central|
|27.||Unger JB, Soto DW, Leventhal A: E-cigarette use and subsequent cigarette and marijuana use among Hispanic young adults. Drug Alcohol Depend 2016; 163: 261–4 CrossRef MEDLINE|
|28.||Wills TA, Knight R, Sargent JD, Gibbons FX, Pagano I, Williams RJ: Longitudinal study of e-cigarette use and onset of cigarette smoking among high school students in Hawaii. Tob Control 2017; 26: 34–9 CrossRef MEDLINE PubMed Central|
|29.||Leventhal AM, Stone MD, Andrabi N, et al.: Association of e-cigarette vaping and progression to heavier patterns of cigarette smoking. JAMA 2016; 316: 1918–20 CrossRef MEDLINE PubMed Central|
|30.||Hammond D, Reid JL, Cole AG, Leatherdale ST: Electronic cigarette use and smoking initiation among youth: a longitudinal cohort study. CMAJ 2017; 189: E1328–36 CrossRef MEDLINE PubMed Central|
|31.||Bold KW, Kong G, Camenga DR, et al.: Trajectories of e-cigarette and conventional cigarette use among youth. Pediatrics 2018; 141: e20171832 CrossRef MEDLINE|
|32.||Primack BA, Shensa A, Sidani JE, et al.: Initiation of traditional cigarette smoking after electronic cigarette use among tobacco-naive U.S. young adults. Am J Med 2018; 131: 443.e1–443.e9 CrossRef MEDLINE|
|33.||Watkins SL, Glantz SA, Chaffee BW: Association of noncigarette tobacco product use with future cigarette smoking among youth in the Population Assessment of Tobacco and Health (PATH) study, 2013–2015. JAMA Pediatr 2018: 172: 181–7 CrossRef MEDLINE|
|34.||Best C, Haseen F, Currie D, et al.: Relationship between trying an electronic cigarette and subsequent cigarette experimentation in Scottish adolescents: a cohort study. 2017 pii: tobaccocontrol-2017–053691.|
|35.||Conner M, Grogan S, Simms-Ellis R, et al.: Do electronic cigarettes increase cigarette smoking in UK adolescents? Evidence from a 12-month prospective study. Tob Control 2017; Epub ahead of print CrossRef MEDLINE|
|36.||Lozanoa P, Barrientos-Gutierrez I, Arillo-Santillan E, et al.: Longitudinal study of electronic cigarette use and outset of conventional cigarette smoking and marijuana use among Mexican adolescents. Drug Alcohol Depend 2017; 180: 427–30 CrossRef MEDLINE|
|37.||Soneji S, Barrington-Trimis JL, Wills TA, et al.: Association between initial use of e-cigarettes and subsequent cigarette smoking among adolescents and young adults: a systematic review and meta-analysis. JAMA Pediatr 2017; 171: 788–97 CrossRef MEDLINE PubMed Central|
|38.||Zuckerman M, Kuhlman DM: Personality and risk-taking: common biosocial factors. J Pers 2000; 68: 999–1029 CrossRef|
|39.||Hanewinkel R, Isensee B: Risk factors for e-cigarette, conventional cigarette, and dual use in German adolescents: a cohort study. Prev Med 2015; 74: 59–62 CrossRef MEDLINE|
|40.||Hammer GP, du Prel JB, Blettner M: Avoiding bias in observational studies: part 8 in a series of articles on evaluation of scientific publications. Dtsch Arztebl Int 2009; 106: 664–8 VOLLTEXT|
|e1.||Siqueira LM, Committee On Substance Use and Prevention: Nicotine and tobacco as substances of abuse in children and adolescents. Pediatrics 2017; 139: e20163436 CrossRef MEDLINE|
|e2.||Orth B, Töppich J: Rauchen bei Jugendlichen und jungen Erwachsenen in Deutschland 2014. Ergebnisse einer aktuellen Repräsentativbefragung und Trends. Köln: Bundeszentrale für Gesundheitliche Aufklärung 2015.|
|e3.||Jamal A, Gentzke A, Hu SS, et al.: Tobacco use among middle and high school students—United States, 2011–2016. MMWR Morb Mortal Wkly Rep 2017; 66: 597–603 CrossRef MEDLINE PubMed Central|
|e4.||Chaffee BW, Couch ET, Gansky SA: Trends in characteristics and multi-product use among adolescents who use electronic cigarettes, United States 2011–2015. PLoS One 2017; 12: e0177073 CrossRef MEDLINE PubMed Central|
|e5.||Hanewinkel R, Tomczyk S, Goecke M, Isensee B: Preventing binge drinking in adolescents. Dtsch Arztebl Int 2017; 114: 280–7 VOLLTEXT|
|e6.||Woicik PA, Stewart SH, Pihl RO, Conrod PJ: The substance use risk profile scale: a scale measuring traits linked to reinforcement-specific substance use profiles. Addict Behav 2009; 34: 1042–55 CrossRef MEDLINE|
|e7.||Zou G: A modified poisson regression approach to prospective studies with binary data. Am J Epidemiol 2004; 159: 702–6 CrossRef|
Deutsches Aerzteblatt Online, 201810.3238/arztebl.2018.0478a
Deutsches Aerzteblatt Online, 201810.3238/arztebl.2018.0477b
Bundesgesundheitsblatt - Gesundheitsforschung - Gesundheitsschutz, 201810.1007/s00103-018-2822-z
Deutsches Aerzteblatt Online, 201810.3238/arztebl.2018.0233
Deutsches Aerzteblatt Online, 201810.3238/arztebl.2018.0479b
Sex Difference in the Association between Electronic Cigarette Use and Subsequent Cigarette Smoking among U.S. Adolescents: Findings from the PATH Study Waves 1–4International Journal of Environmental Research and Public Health, 202110.3390/ijerph18041695
Deutsches Aerzteblatt Online, 201810.3238/arztebl.2018.0477a
South African Journal of Psychology, 201910.1177/0081246318794828
Deutsches Aerzteblatt Online, 201810.3238/arztebl.2018.0479a
Deutsches Aerzteblatt Online, 201810.3238/arztebl.2018.0478b
Deutsches Aerzteblatt Online, 201910.3238/arztebl.2019.0577
Electronic Cigarette Use and Smoking Initiation in Taiwan: Evidence from the First Prospective Study in AsiaInternational Journal of Environmental Research and Public Health, 201910.3390/ijerph16071145
E-cigarette use and combustible tobacco cigarette smoking uptake among non-smokers, including relapse in former smokers: umbrella review, systematic review and meta-analysisBMJ Open, 202110.1136/bmjopen-2020-045603