18B.6Effects of e-cigarette use on smoking

Last updated: October 2021
Suggested citation: Greenhalgh, EM, & Scollo, MM. 18B.6 Effects of e-cigarette use on smoking. In Greenhalgh, EM, Scollo, MM and Winstanley, MH [editors]. Tobacco in Australia: Facts and issues. Melbourne: Cancer Council Victoria; 2021. Available from:  http://www.tobaccoinaustralia.org.au/chapter-18-harm-reduction/indepth-18b-e-cigarettes

 

At the heart of the debate over e-cigarettes is the extent to which the potential benefits of making a product that may help smokers to quit might be outweighed by several potential risks. Risks identified to date include uptake by non-smokers, gateway effects, dangers associated with dual use, discouragement from smoking cessation, renormalising smoking, and allowing the tobacco industry to influence decision-making in public health (see Section 18B.7 for a discussion of potential population-level risks and benefits).1-3

Consumers of e-cigarettes report mixed reasons for their use. Dual users of tobacco and e-cigarettes commonly report vaping as a substitute for smoking, either in an attempt to reduce consumption of cigarettes, or to enable nicotine use in situations where use of traditional cigarettes would not be allowed or acceptable (see Section 18B.11). As indicated in Section 18.3, health risks associated with smoking are unlikely to be reduced by e-cigarettes if users continue to smoke. Crucial to assessing the potential public health benefits of increasing use of e-cigarettes, then, is whether such use will increase or decrease the likelihood of a smoker eventually quitting tobacco.4 That is, whether use of e-cigarettes increases or decreases

  • the likelihood of smokers making quit attempts
  • the likelihood of a given quit attempt being successful
  • the likelihood of reducing use of cigarettes eventually leading to quitting
  • the likelihood that use of e-cigarettes among ex-smokers prevents relapse.

Smoking poses a very significant risk to health both in the immediate and the longer term, but the most serious diseases emerge only with long-term use. While two of every three long term smokers in Australia will die from smoking, quitting prior to age 45 reduces mortality risk close to that of never smokers.5 Given that complete cessation of use of any nicotine product is the option associated with least harm, it follows that the optimal approach for younger smokers at least in the first instance would be to attempt to quit without continuing use of nicotine.

18B.6.1 A ‘gateway effect’ to tobacco smoking among young people

Of great concern to public health experts is the growing body of research suggesting a possible relationship between e-cigarette use and the uptake and escalation of smoking among young people.  A 2016 meta-analysis concluded that never-smoking adolescents and young adults who use e-cigarettes are more likely to intend to smoke,6 and a systematic review in the same year concluded that e-cigarette use is associated with an increase in smoking, even among adolescents not susceptible to smoking.7 A major review published by the US National Academies of Science, Medicine and Engineering in 2018 concluded that there is substantial evidence that e-cigarette use increases risk of ever using combustible tobacco cigarettes among youth and young adults,8 and another major review published by the Australian CSIRO later in the same year concluded that the evidence for a strong positive relationship between use of e-cigarettes and later cigarette smoking among youth continues to accumulate.9 A 2019 meta-analysis found that e-cigarette use by adolescents is associated with a 2- to 4-fold increase in cigarette smoking over the next year.10 A major review and meta-analysis by funded by the Australian Government Department of Health published in 2021 found that never smokers who used e-cigarettes had about three times the odds of smoking initiation compared with non-e-cigarette users.11 Additional longitudinal studies,12-19 and several less extensive  reviews20 and meta-analyses,21-26 have similarly concluded that e-cigarette use is associated with an increased risk of cigarette smoking. One Australian study published in 2021 found that, among a cohort of young women, those who had ever used e-cigarettes had 3.7 times greater odds of taking up smoking.27

Compared with older teenagers, onset of e-cigarette use at a younger age appears to be associated with increased odds of smoking.28-30 The relationship between e-cigarette use and smoking uptake may also be stronger among boys than girls.31 Australian researchers found that, among young adults who had never smoked, curiosity, willingness and intentions to smoke tobacco cigarettes were higher among young e-cigarette users than never users.32 Other studies have found that factors such as more frequent e-cigarette use,33 social anxiety,34 White race (compared with Black),35, 36 and middle socioeconomic status (compared to low),35 increase the likelihood of transitioning from e-cigarette use to cigarette/dual use. Several studies have suggested that the relationship may be bi-directional, such that smoking increases the risk of e-cigarette use, and e-cigarette use increases the risk of smoking.37-40 Use of e-cigarettes among youth and young adults may increase consumption of conventional cigarettes and duration of smoking.8, 41 E-cigarette susceptibility and use may also predict uptake of other types of tobacco products,16, 42 as well as marijuana and alcohol use over time.43-46

Studies such as those described above cannot establish that e-cigarette use causes smoking. E-cigarette use could be a marker in young people who would have gone on to smoke regardless;  it is possible that the relationship between e-cigarette use and smoking could be explained by another/other variable/s, such as social—environmental factors, or a common genetic vulnerability.22, 23, 47-50 However several studies have noted conventional cigarette uptake among e-cigarette users who would be considered least at risk of smoking,7, 12, 51-54 and the best-quality studies and reviews have attempted to control for underlying susceptibility. Several possible mechanisms of how e-cigarette use may act as a ‘gateway’ to smoking have been proposed. E-cigarette use could normalise nicotine use and smoking behaviours more generally, leading to the renormalisation of smoking. It could also cause users to develop nicotine addiction,6, 51 with research showing that the use of e-cigarettes with higher concentrations of nicotine has a stronger association to later cigarette use.9, 55

Alternatively, some have suggested that, rather than acting as a ‘gateway’, e-cigarettes may be acting as a ‘diversion’ among young people. That is, e-cigarette use partially or wholly replaces cigarette smoking, and may therefore accelerate the decline in youth cigarette smoking.56 They note that increases in use of non-cigarette tobacco/nicotine products has increased substantially in the US56 and UK,57 alongside a decline in cigarette smoking. US researchers also found that this overall increase in product use has not been accompanied by an increase in nicotine dependence among students, with use of e‐cigarettes associated with lower levels of dependence than other products.58 Several studies from the US have concluded that a long-term decline in smoking prevalence among youth and young adults accelerated after e-cigarette use became more widespread, which the authors argue demonstrates that e-cigarette use has not increased youth smoking at the population level and may support the diversion theory.59-61 Another argued that data on adolescent tobacco/nicotine use from 2000 to 2019 in the US is more consistent with a diversion effect than a catalyst/gateway effect.62 However, critics of this theory argue that continued declines in smoking might alternatively be attributed to the continuing and long-term effects of current and historical comprehensive tobacco control programs.63, 64  To put it another way, declines may have been accelerating due to the cumulative and social contagion effects of previous decades of policy, and may have been steeper still without e-cigarette use.  Another US study found that while the introduction of e-cigarettes was followed by a faster decline in ever use of cigarettes among young people, there was a slower decline in current cigarette smoking, which the authors argue suggests that e-cigarettes are not acting as a substitute for cigarettes.65

18B.6.2 Effects on attempts to quit smoking

Many smokers report using e-cigarettes as a cessation aid.66, 67 In Australia in 2020, about one in five (22%) smokers or recent ex-smokers reported having used e-cigarettes in their last quit attempt, compared with 27% in Canada, 37% in England, and 22% in the US.68 A randomised controlled trial in Australia reported that e-cigarettes were chosen more frequently than NRT by trial participants (71.1% vs. 29.0%).69

A large study in England found no clear association between e-cigarette use and prevalence of quit attempts; it also found that such use was associated with a decrease in the use of prescription NRT.70 A subsequent English study found that dual use of e-cigarettes was associated with a slightly higher quit attempt rate than exclusive smoking, but lower than for dual use of NRT.71 A number of other studies have found smokers who use e-cigarettes are more likely to attempt to quit conventional cigarettes.72-80 However, this may be due to greater motivation (i.e. smokers who use e-cigarettes are already more interested in quitting smoking than those who do not use them).9 Among teenagers, research in the US found no association between use of e-cigarettes and tobacco smoking quit attempts.81

18B.6.3 Effects on success in quitting smoking

While the use of e-cigarettes may be associated with increased quit attempts, findings have been mixed as to whether such attempts translate to increased long-term cessation.72, 73, 75, 77-79  Major reviews of the effectiveness of e-cigarettes as a cessation aid have been published by Public Health England,82 the US National Academies of Sciences, Engineering, and Medicine,8 and the CSIRO in Australia.9 Overall, these concluded that e-cigarettes may be effective cessation aids in the short-term, particularly when the products contain nicotine.8, 9, 82 However, the CSIRO report concludes that it is unclear whether use of e-cigarettes leads to long-term cessation, or whether they are as effective as other forms of cessation support (such as NRT).9 A Cochrane review published in 2021 found moderate certainty evidence that users of nicotine e-cigarettes were 1.7 times more likely to successfully quit than those who used NRT and also about 1.7 times more likely to successfully quit than those who used non-nicotine e-cigarettes.83 Along with using e-cigarettes that contain nicotine,84 sustained75 and frequent85-96 e-cigarette users appear to be more likely to successfully quit than those who use the products short-term or intermittently. Infrequent e-cigarette users—who comprise the majority of users—may be less likely to quit, with research showing an association between non-daily use and both lower motivation to quit85 and lower rates of successful cessation.88, 93, 94 Some research has found support for the role of sweet/fruit flavours in quitting compared with tobacco or menthol,94, 95, 97 while others have found no differences in quit attempts between users of different flavours.98 Use of disposable e-cigarettes may also be associated with a lower likelihood of quit attempts compared with other product types.95, 96, 99

Each of the reviews to date note the limited/low quality nature of the evidence,84, 100-112 and call for long-term randomised controlled trials (RCTs). A meta-analysis published in 2021 that only included RCTs found that participants who used nicotine e-cigarettes were 49% more likely to successfully quit than those who received nicotine replacement therapy, and 109% more likely than those in control conditions who were not provided with any form of nicotine replacement. However, it notes that most studies had moderate–high risk of bias.113 Additional meta-analyses similarly found modest evidence that nicotine e-cigarettes were more effective than placebo, NRT,25, 114 or counselling for smoking cessation.114 One review and meta-analysis noted that while there was low certainty evidence to support the use of e-cigarettes for short-term cessation, there is a lack of long-term safety and efficacy data.115 A further meta-analysis of RCTs comparing e-cigarettes with NRT published in 2021 found no differences in cessation outcomes, however also notes the low quality nature of the evidence, and that only five studies met criteria for inclusion.116 A preprint of a systematic review and meta-analysis (i.e., it has not yet been peer reviewed) commissioned by the Australian government concluded that there is currently insufficient evidence that e-cigarettes—with or without nicotine—are effective cessation aids compared with no intervention, placebo or NRT, but notes that there is some promising evidence that e-cigarettes may help with cessation.117

A number of population-based studies published in recent years have also explored the association between e-cigarette use and quit rates.92, 118-121 For example, research in England found that the increase in prevalence of e‐cigarette use between 2007 and 2017 was associated with increased success rates of quit attempts and overall quit rates.120 In its latest evaluation, Public Health England reported that in 2017, over 50,000 smokers stopped smoking with a vaping product who would otherwise have continued to smoke. Among people attending stop smoking services, using an e-cigarette as part of quit attempt appeared to be as effective as using cessation medications; however, the proportion of quit attempts using an e-cigarette remained very small (5%).82 Another UK study found that use of NRT or e-cigarettes alongside smoking was associated with an increased likelihood of becoming an ex-smoker, although most ex-smokers had used no nicotine products to quit.122 Cross-sectional research in the EU found an association between e-cigarette use and recent smoking cessation.123 However, findings from the ITC Four country  (US, Canada, Australia, England) study found that dual use of cigarettes and e-cigarettes at baseline (2016) was not associated with cessation for either daily or non-daily smokers two years later.124 Research in the US found that e-cigarette use by adolescent smokers was not associated with subsequent abstinence,125 nor does it appear to be associated with increased cessation among adult smokers compared with non-e-cigarette users126, 127 or compared with users of NRT or cessation medications.128 A review published in 2020 concluded that while e-cigarettes appear to increase cessation when provided for free within RCTs, at the population level, e-cigarette use as a consumer product is not significantly associated with smoking cessation. The authors suggest that that e-cigarettes could be considered on a prescription basis with clinical supervision, and after considering potential risks and benefits.93

18B.6.4 Effects on relapse among ex-smokers

The ITC Four Country study found that while ex-smokers who vaped daily were more likely to perceive that they were still very addicted to smoking, compared with ex-smokers who were not vaping, vapers also reported greater confidence in remaining a non-smoker, which the authors suggest may help to reduce relapse.129 Another paper analysing data from the ITC study found no differences in relapse in 2018 between ex-smokers who were vaping in 2016 compared to those who were not vaping.124 Research in Italy found that among a sample of e-cigarette users who were all ex-smokers, almost two-thirds remained abstinent six years later.130 However, longitudinal research in France found that e-cigarette use was associated with an increase in the rate of smoking relapse among ex-smokers, although the authors note that relapse was not higher among ex-smokers who had quit in recent years.119 Several studies in the US have also suggested that e-cigarette use is associated with relapse among ex-smokers,131-134 with one study finding intermittent users may be more likely to relapse to smoking than those who vape daily.135 Longitudinal research in the US found that while dual use was association with cessation, e-cigarette use had a much stronger relationships with smoking both smoking initiation and relapse.136 Survey research in South Africa found that odds of relapse for smokers trying to quit were higher among ever, former and current e-cigarette users than never e-cigarette users.137 A systematic review and meta-analysis published in 2021 found evidence that that ex-smokers who use e-cigarettes have more than twice the odds of relapse compared with ex-smokers who have not used e-cigarettes.11 Another similarly concluded that ex-smokers who used e-cigarettes—particularly long-term ex-smokers—had an increased risk of relapse to smoking compared with non-e-cigarette users.138

18B.6.5 Cutting down as a step towards quitting

Reduced daily consumption of conventional cigarettes in users of e-cigarettes have been noted in several studies,80, 139-141 and reviews;103, 104 however, this may not lead to meaningful changes in consumption at a population level.142 One study found that although dual use reduced cigarette consumption, total nicotine use and dependence increased, which could hinder the ability to quit either or both products.141 Longitudinal findings from the ITC Four Country surveys showed that among daily smokers, vaping appeared to have been helpful in reducing daily smoking to non-daily smoking, but did not improve rates of quitting.124

Even following substantial reductions in cigarette consumption, evidence suggests that the health benefits are limited. Although smokers who substantially reduce the number of cigarettes smoked per day reduce their exposure to some harmful and potentially harmful constituents, these decreases are limited and much smaller in magnitude than reductions following complete cessation.143 Several large cohort studies have found that smokers who reduce their consumption do not significantly reduce their risk of premature death.144, 145 Smoking just 1–4 cigarettes per day significantly increases a person’s risk of dying from smoking-related disease.146 This modesty of the health benefit from smoking reduction  is often attributed to compensatory smoking: those who cut down tend to inhale each cigarette more deeply, and smoke more of it.143, 147 (See Section 18.3 for further detail).

A number of studies have shown that dual use of NRT and cigarettes can help alleviate the issue of compensation,148-150 leading some to advocate long-term use of NRT in combination with cutting down as a harm reduction strategy.151, 152 Researchers have suggested that it may be possible that the use of e-cigarettes while smoking could similarly reduce intake of nicotine and toxins from each cigarette. However, data on the long-term safety of e-cigarettes is lacking, and they may be less safe than existing, licenced NRT products.73

The main benefit of cutting down seems to be its role as a step toward quitting.144, 153 A 2015 review exploring the usefulness of cutting down determined that smokers who reduce the number of daily cigarettes smoked are more likely than smokers who do not cut down to attempt to quit and actually achieve smoking cessation. This is particularly the case when the quit attempt is combined with NRT.154 A 2019 Cochrane review concluded that cutting down may result in similar quit rates to going cold turkey, and that reduction‐to‐quit interventions may be more effective when pharmacotherapy is used, particularly fast‐acting NRT or varenicline.155 NRT-assisted reduction appears to be an effective intervention for achieving sustained smoking abstinence, particularly for smokers not currently intending to quit (or quit abruptly),156, 157 and is effective and cost effective compared to no quit attempt.153 E-cigarettes may similarly prove to be a useful form of NRT in combination with smoking reduction as part of ‘cutting down to quit’, but further research is needed on the efficacy of the products in this context.154

18B.6.6 Prolonged dual use of cigarettes and e-cigarettes

Dual use refers to the concurrent use of conventional tobacco products and e-cigarettes.  Dual use is actively promoted by some e-cigarette manufacturers, especially those that also manufacture tobacco products, as a way for smokers to by-pass smokefree regulations,158 and this is a commonly cited reason for e-cigarette use among smokers.111, 159 Other smokers use both products as a means of cutting down the number of cigarettes they smoke each day, and/or as an intended pathway to complete smoking cessation.4, 160 However, many smokers are unsuccessful in transitioning fully from smoking to vaping, despite initial intentions to quit smoking.159 One study in England found that long-term use of e-cigarettes was similarly prevalent among current and recent ex-smokers, indicating continued dual use was a common pattern, although this was not associated with reduced motivation to quit.161 Research in the US has also found that continued dual use is a common pattern among adults,162, 163 and that among dual users, most are predominant smokers (rather than heavy or light use of both, or predominant vaping). Completely switching from dual use to exclusive e-cigarette use appears to be relatively uncommon,164 with one longitudinal study finding the majority of dual users transitioned to exclusive smoking.163  Also in the US, use of e-cigarettes by young adults is associated with more rather than less frequent and intensive cigarette smoking.165 Another English study found that dual users of e-cigarettes had lower quit attempt rates than dual users of NRT,71 and an Italian study found that dual users were no more likely to quit than exclusive smokers six years later.130

While a reduction in risk seems likely for smokers who completely substitute tobacco cigarettes for e-cigarettes,166, 167 the benefits for those who continue to use some tobacco cigarettes are much less certain; as noted above, even ‘light’ cigarette smoking carries substantial health risks—see Section 18.3. Among those who exclusively smoke tobacco cigarettes, cutting down the number of cigarettes consumed may not reduce toxic exposure if smokers compensate by drawing more deeply on the cigarettes they do smoke. There is some evidence that supplementing reduced cigarette consumption with an alternative source of nicotine might reduce toxicant exposure and hence mortality among smokers who continue to smoke at a reduced rate.144, 145, 168  However, there is no available evidence whether or not long-term e-cigarette use among smokers changes morbidity or mortality compared with those who only smoke tobacco cigarettes.8 Use of e-cigarettes has the potential to introduce independent or additive health risks.9, 169 Targeted smoking cessation interventions for dual users have been developed with the understanding that most will continue to smoke.170

 

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