Gateway Effects: Why the Cited Evidence Does Not Support Their Existence for Low-Risk Tobacco Products (and What Evidence Would)

Analysis of common methodological flaws in the highest cited e-cigarette epidemiology research

The prevalence of vaping, also known as using e-cigarettes, vapes and vape pens, has prompted a demand for reliable, evidence-based research. However, published literature on the topic of vaping often raises concerns, characterized by serious flaws and a failure to adhere to accepted scientific methodologies. In this narrative review, we analyze popular vaping studies published in medical journals that purport to evaluate the association of vaping and smoking cessation, smoking initiation or health outcomes. We analyzed 24 included studies to identify the questions they claimed to address, stated methods, manner of implementation, discussions, and stated conclusions. After critical appraisal, we noted a multiplicity of flaws in these studies, and identified patterns as to the nature of such flaws. Many studies lacked a clear hypothesis statement: to the extent that a hypothesis could be inferred, the methods were not tailored to address the question of interest. Moreover, main outcome measures were poorly identified, and data analysis was further complicated by failure to control for confounding factors. The body of literature on "gateway" theory for the initiation of smoking was particularly unreliable. Overall, the results and discussion contained numerous unreliable assertions due to poor methods, including data collection that lacked relevance, and assertions that were unfounded. Many researchers claimed to find a causal association while not supporting such findings with meaningful data: the discussions and conclusions of such studies were, therefore, misleading. Herein, we identify the common flaws in the study design, methodology, and implementation found in published vaping studies. We present our summary recommendations for future vaping research. Our aim is to prompt future researchers to adhere to scientific methods to produce more reliable findings and conclusions in the field of vaping research.

From gateways to multilinear connections: A qualitative longitudinal investigation of the relationships between vaping and smoking among adolescent users

BACKGROUND

The international growth of e-cigarette use has been accompanied by a corresponding concern that e-cigarettes will act as a 'gateway' to smoking and the use of other drugs. Taking these concerns as our point of departure, we explore the relationships between vaping and smoking among a cohort of young people.

METHODS

Qualitative longitudinal methods with a diverse sample of 36 14-18-year olds from the UK city of Leicester. A total of 66 depth interviews conducted across two phases separated by 6-12 months. The interviews were recorded, transcribed verbatim and thematically analysed.

FINDINGS

We highlight a complex 'tangle' of connections between substances/risk behaviours recounted to us by our adolescent study participants, including multiple and multilinear relationships between vaping and smoking. These findings problematise some of the core axioms of the notion of gateways as an explanatory model of causality and sequential connection between smoking and vaping. They also throw into question gateway logics more fundamentally. While many of our study participants themselves consciously invoked ideas of 'gateway effects', the accounts they produced repeatedly disrupted the logics of connection (between e-cigarettes and smoking; one set of behaviours and another) presupposed in gateway theory and our own early lines of questioning. Accordingly, we explore how cultural understandings of gateway effects are invoked by users in accounting for their vaping and smoking behaviours, noting the potential influence of these ideas upon the very processes they are understood to apprehend.

CONCLUSION

Our findings suggest there is a case to be made to reinforce the distinctiveness of tobacco and e-cigarettes in the life-worlds of young people to avoid naturalising a 'gateway' logic of connection that might ultimately inform the associative logic of young users themselves, and potentially the development of their usage careers.

Longitudinal transitions of cigarettes and electronic nicotine delivery systems among adolescents: Construction of a retrospective cohort using recall data from a cross-sectional sample

INTRODUCTION

A major concern regarding non-cigarette tobacco or nicotine products (NCTNPs) is whether they facilitate or mitigate overall tobacco or nicotine use. We examined longitudinal transitions of cigarettes and electronic nicotine delivery systems (ENDS) by constructing a retrospective cohort based on the recall data of a cross-sectional sample.

METHODS

Using the Korea Youth Risk Behavior Survey, we constructed crosssectional data of 59576 adolescents into retrospective cohort data. Participants were categorized into 4 mutually exclusive tobacco or nicotine use states. We used a multistate Markov model to identify transitions between the states to calculate transition intensity ratios (TIRs), and examined the current use of tobacco or nicotine products to assess both gateway effects to cigarettes, and whether ENDS use helps adolescents quit cigarette smoking.

RESULTS

Compared with never use, use of ENDS was associated with an increased risk of initiation of cigarette use (TIR=6.8; 95% CI: 4.5-10.2). The risk of transitioning from cigarette ever use to ENDS, compared with never use to ENDS, was even more pronounced (TIR=44.1; 95% CI: 34.1-56.9). The prevalence of current cigarette smoking was higher among those who started ENDS then cigarettes, compared to those who began cigarette use without experimenting with ENDS (43.1% vs 35.8%). Moreover, 27.8% (95% CI: 23.6-32.0%) of adolescents who experimented first with cigarettes then moved to ENDS were current users of cigarettes, and 46.4% (95% CI: 42.1-51.1%) of these adolescents were current users of both cigarettes and ENDS.

CONCLUSIONS

Based on the recall data of a cross-sectional sample, we demonstrate that ENDS experimentation increases the likelihood of cigarette smoking initiation. A significant proportion of these adolescents continue to use cigarettes. Moreover, those who experimented with cigarettes then ENDS also continue smoking cigarettes or both cigarettes and ENDS. We suggest comprehensive tobacco control policies for all tobacco/nicotine products and monitoring the timing of NCTNP initiation in cross-sectional surveys.

The greater use of flavoured snus among ever-smokers versus never-smokers in Norway

Background

Similar to the debate around e-cigarettes, an increase in snus use among Norwegian adolescents has prompted debate on whether flavour options in snus should be limited. To this end, we compared use of flavoured snus among snus users with different smoking status.

Methods

Questions about flavoured snus use were included in an online omnibus study conducted from 2015 to 2019 (N = 65,445) that included 16,295 ever snus users (aged 15+). Current snus users (N = 9783) were asked “Do you usually use snus that has a flavouring (liquorice, mint, wintergreen, etc.)? Adjusted predicted probabilities and 95% confidence intervals (CI) were calculated from a logistic regression model.

Results

Less than 25% of the snus users reported never having smoked. The overall probability of using flavoured snus was .45 (95% CI .44–.46), highest among daily (.51, 95% CI .47–.54) and former daily smokers (.50, 95% CI .48–.52), and lowest among never (.41, 95% CI .39–.43) and occasional smokers without any prior history of daily smoking (.41, 95% CI .38–.44). Use of flavoured products was higher among female snus users (p = .67, 95% CI .65–.69) compared to males (p = .35, 95% CI .34–.36), highest among the youngest age group, 15–24 years (p = .58, 95% CI .56–.60) and decreased with increasing age.

Conclusion

Regulation that would ban or limit flavoured snus use may affect smokers—an at risk population—more than never smokers. The health authorities should be mindful of the real-world complexity governing potential harms and benefits of flavour restrictions on snus. A further assessment of flavour limitations should acknowledge that flavoured snus products also function as alternatives to cigarettes.

Exploring Associations between Susceptibility to the Use of Electronic Nicotine Delivery Systems and E-Cigarette Use among School-Going Adolescents in Rural Appalachia

Electronic nicotine delivery systems (ENDS) use, including e-cigarettes, has surpassed the use of conventional tobacco products. Emerging research suggests that susceptibility to e-cigarette use is associated with actual use among adolescents. However, few studies exist involving adolescents in high-risk, rural, socioeconomically distressed environments. This study examines susceptibility to and subsequent usage in school-going adolescents in a rural distressed county in Appalachian Tennessee using data from an online survey (N = 399). Relying on bivariate analyses and logistic regression, this study finds that while 30.6% of adolescents are ever e-cigarette users, 15.5% are current users. Approximately one in three adolescents are susceptible to e-cigarettes use, and susceptibility is associated with lower odds of being a current e-cigarette user (OR = 0.03; CI: 0.01–0.12; p < 0.00). The age of tobacco use initiation was significantly associated with decreased current use of e-cigarettes (OR = 0.89; CI: 0.83–0.0.97; p < 0.01). Overall, the results of this exploratory study suggest the need for larger studies to identify unique and generalizable factors that predispose adolescents in this high-risk rural, socioeconomically disadvantaged region to ENDS use. Nevertheless, this study offers insight into e-cigarette usage among U.S adolescents in rural, socioeconomically disadvantaged environments and provides a foundation for a closer examination of this vulnerable population.

Gateway effects and electronic cigarettes

BACKGROUND

E-cigarettes are alleged to be a gateway to cigarette smoking in non-smokers. This study examines whether the gateway theory has value, whether the criteria to establish causality have been met and what type of evidence is required to test this theory.

ANALYSIS

Experiments are impractical, and we may not be able to test properly the gateway effects via observational studies that simply adjust for confounders. Multivariate models cannot eliminate all the variance in propensity to smoke captured by the variable 'vaping' because of the proximity of these two behaviours. It may be difficult to prove that vaping precedes smoking when product use co-occurs and when, in fact, smoking usually precedes vaping. The gateway theory is not compatible with either (1) the decrease in smoking prevalence observed in adolescents in countries where vaping increased or (2) an increase in smoking among teenagers after age restrictions were imposed on e-cigarette purchases. A spurious gateway effect can be produced artificially by mathematical models in which a propensity to use substances is correlated with opportunities to use substances. Finally, neither nicotine medications nor smokeless tobacco produce gateway effects. Available data are compatible with a common liability model in which people who are liable to use nicotine are more likely to use both e-cigarettes and cigarettes.

CONCLUSIONS

Despite its weaknesses and scant empirical support, the gateway theory of smoking initiation has had enormous political influence. Policies based on this theory will not have the intended effects if the association between vaping and smoking is explained by common liabilities.

Evaluating the mutual pathways among electronic cigarette use, conventional smoking and nicotine dependence

BACKGROUND AND AIMS

The implications of the rapid rise in electronic cigarette (e-cigarette) use remain unknown. We examined mutual associations between e-cigarette use, conventional cigarette use and nicotine dependence over time to (1) test the association between e-cigarette use and later conventional smoking (both direct and via nicotine dependence), (2) test the converse associations and (3) determine the strongest pathways predicting each product's use.

DESIGN

Data from four annual waves of a prospective cohort study were analyzed. Path analysis modeled the bidirectional, longitudinal relationships between past-month smoking frequency, past-month e-cigarette frequency and nicotine dependence.

SETTING

Chicago area, Illinois, USA.

PARTICIPANTS

A total of 1007 young adult smokers and non-smokers (ages 19-23 years).

MEASUREMENTS

Frequency of (1) cigarettes and (2) e-cigarettes was the number of days in the past 30 on which the product was used. The Nicotine Dependence Syndrome Scale measured nicotine dependence to cigarettes.

FINDINGS

E-cigarette use was not associated significantly with later conventional smoking, either directly (β = 0.021, P = 0.081) or through nicotine dependence (β = 0.005, P = 0.693). Conventional smoking was associated positively with later e-cigarette use, both directly (β = 0.118, P < 0.001) and through nicotine dependence (β = 0.139, P < 0.001). The strongest predictors of each product's use was prior use of the same product; this pathway was strong for conventional cigarettes (β = 0.604, P < 0.001) but weak for e-cigarettes (β = 0.120, P < 0.001). Nicotine dependence moderately strongly predicted later conventional smoking (β = 0.169, P < 0.001), but was a weak predictor of later e-cigarette use (β = 0.069, P = 0.039).

CONCLUSIONS

Nicotine dependence is not a significant mechanism for e-cigarettes' purported effect on heavier future conventional smoking among young adults. Nicotine dependence may be a mechanism for increases in e-cigarette use among heavier conventional smokers, consistent with e-cigarettes as a smoking reduction tool. Overall, conventional smoking and, to a lesser extent, its resulting nicotine dependence, are the strongest drivers or signals of later cigarette and e-cigarette use.

Young or adult users of multiple tobacco/nicotine products urgently need to be informed of meaningful differences in product risks

Previously, it has been argued that health information efforts need to inform the public about meaningful differential risks from tobacco/nicotine products. The fact of multiple product use by the same individual further supports this need. When the majority of youth, for example, who use smokeless tobacco are also current tobacco smokers, it makes little sense to mount a smokeless prevention campaign that fails to include clear messages about the much greater risks from smoking. In April 2016, The Food & Drug Administration (FDA) announced a $36 million campaign for youth that "smokeless doesn't mean harmless." Research shows the public (a) already knows that smokeless tobacco is not harmless, but are (b) also largely unaware that cigarettes are much more harmful than smokeless. Though not harmless, smokeless tobacco has been estimated to be over 90% less harmful than cigarettes. 'Gateway' fears are made moot by current use of multiple tobacco/nicotine products. When multi-tobacco product use is commonplace among users, usable information on significant differences in risk is crucial for both adult and younger users. The FDA and like campaigns and health information websites should follow established ethical principles and accepted communication methods to inform the public of less-harmful tobacco/nicotine products as well as the greater harms of smoking, in keeping with the Surgeon-General's advice that reductions in smoking in particular will bring about the greatest public health advances.

A Risk Assessment Matrix for Public Health Principles: The Case for E-Cigarettes

Besides nicotine replacement therapies, a realistic alternative for smoking cessation or for smoking substitution may come from electronic cigarettes (ECs), whose popularity has been steadily growing. As for any emerging behaviour associated with exposure to inhalational agents, there is legitimate cause for concern and many health organizations and policy makers have pushed for restrictive policy measures ranging from complete bans to tight regulations of these products. Nonetheless, it is important to reframe these concerns in context of the well-known harm caused by cigarette smoking. In this article, we discuss key public health principles that should be considered when regulating ECs. These include the concept of tobacco harm reduction, importance of relative risk and risk continuum, renormalization of smoking, availability of low-risk product, proportionate taxation, and reassessment of the role of non-tobacco flavours. These public health principles may be systematically scrutinized using a risk assessment matrix that allows: (1) to determine the measure of certainty that a risk will occur; and (2) to estimate the impact of such a risk on public health. Consequently, the ultimate goal of responsible ECs regulation should be that of maximizing the favourable impact of these reduced-risk products whilst minimizing further any potential risks. Consumer perspectives, sound EC research, continuous post-marketing surveillance and reasonable safety and quality product standards should be at the very heart of future regulatory schemes that will address concerns while minimizing unintended consequences of ill-informed regulation.

Health professionals in Flanders perceive the potential health risks of vaping as lower than those of smoking but do not recommend using e-cigarettes to their smoking patients

Background

Many misperceptions of both risks and opportunities of e-cigarettes (e-cigs) exist among the general population and among physicians, although e-cigs could be a valuable harm reduction tool for current smokers.

Methods

Two groups in Flanders, namely general practitioners (GPs; family doctors) and tobacco counselors filled out an online questionnaire with regard to their attitudes and risk perceptions concerning e-cigs. Statements included were on the safety and the addictive properties of e-cigs in absolute terms, whereas other items compared e-cigs with regular tobacco cigarettes. Statements about possible “gateway” and “renormalization” effects, selling to minors, and use in public places and on the potential of e-cigs as a smoking cessation aid were also included. Respondents were also asked for the rate at which their patients asked information about e-cigs, if they would recommend e-cigs to their smoking patients, and whether they had information brochures on e-cigs.

Results

About 70 % believed that e-cigs are harmful to vapers, and about half to two thirds believed that e-cigs are carcinogenic, increase cardiovascular risk, and increase the risk of chronic lung disease. Also, a substantial minority incorrectly believed these risks to be no less than those resulting from regular smoking. Ten to almost 20 % disagreed that e-cigs are healthier and represent less risk for the main serious smoking-related diseases than conventional cigarettes. More than half of the respondents disagreed that e-cigs are an effective smoking cessation aid. None (0 %) offered the strongest level of agreement for recommending e-cigs to their clients/patients, but GPs agreed to a lesser degree a bit more often than tobacco counselors. Almost none had information leaflets for potentially interested patients. Finally, the majority of our sample also believed that e-cigs will cause renormalization of smoking and that e-cigs will lead to an uptake of conventional smoking and disagreed with allowing vaping in enclosed public places.

Conclusions

Health professionals in Flanders perceive the potential health risks of vaping as lower than those of smoking but do not recommend using e-cigs to their smoking patients.