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Section III Public Health Implications of E-Cigarettes While e-cigarettes might cause youth who use them to transition to use of combustible tobacco products, they could increase adult cessation of combustible tobacco cigarettes if they are used frequently. Across a range of studies and outcomes e-cigarettes pose less risk to an individual than combustible tobacco cigarettes. With the range of assumptions used, population modeling projects that there would be net public health harm in the short and long term if the products do not increase combustible tobacco cessation in adults. Factors that would maximize potential health benefits associated with these products include determining with more precision whether and under which conditions e-cigarettes could serve as an effective smoking cessation aid, discouraging their use among youth through standard tobacco control strategies such as education and access restrictions, and increasing their safety through data-driven engineering and design. Understanding the public health implications of e-cigarette use at the population level requires consideration of not only the risks of e-cigarettes on individual health outcomes, as described in the preceding chapters, but also the relation between e-cigarette use and use of other tobacco productsânamely, combustible tobacco cigarettes. Given the well-documented and strong influence of combustible tobacco cigarette smoking on health (HHS, 2014) and the emerging evidence that, although not harm free, e-cigarettes likely expose users to lower health risks compared with combustible tobacco cigarettes, any link between e-cigarette use and patterns of combustible tobacco cigarette smoking would have a considerable impact on both individual and population health. Thus, a question relevant to the committeeâs task is whether and to what extent e-cigarette use affects patterns of combustible tobacco cigarette smoking. The challenge of evaluating the effect of e-cigarette use on combustible tobacco cigarette use is that e-cigarettes could influence combustible tobacco cigarette smoking through a number of pathways, which together could lead to net public health benefit or harm. To understand the potential effects of e-cigarette use on combustible tobacco cigarette smoking, the committee developed a conceptual framework illustrating these plausible pathways, or the possible transitions among e-cigarette use, cigarette smoking, and non-use (see Figure). There are many PREPUBLICATION COPY: UNCORRECTED PROOFS
S III-2 PUBLI HEALTH CONSEQU IC H UENCES OF E-CIGARET F TTES FIGURE Smoking tr E ransitions be etween e-cig garette use, c cigarette smo oking, and n non-use. plausible pathways, and smoking and tobacco use traject e a g tories are oft complex. To assess t ten the potential effects of e- -cigarette use on combus stible tobacc cigarette s co smoking and correspond d ding health eff ffects, this se ection of the report focus on the in fluence of e- ses -cigarette us on cigaret se tte use initia ation and ces ssation, as well as the ha from e-c w arm cigarettes relative to com mbustible tobbacco cigarettess. Combustible tobacco ciga C arette initiati reflects t ion transitions frrom no smok king to established or regular smoking, and therefore involves m r a e multiple steps within the tobacco s progressi trajectory Conseque ion y. ently, to stud markers a dy along he cont tinuum of sm moking initiaation, the comm mittee first exxamined tran nsitions from never smo m oking combu ustible tobacc cigarettes to co s any repor of ever using combust rt tible tobacco cigarettes, alone or con o ncurrent with e-cigarette h es (dual use Ever use could reflect either a per e). c t riod of tempoorary experi imentation th does not hat progress to regular sm moking or th beginning of a trajecto toward b he g ory becoming a r regular smokker. Thus, the committee then examin the progression to be e ned ecoming a re egular smok as indicat ker ted by increa in the fr ases requency (i.e number of days used i past 30), i e., f in intensity (i.e cigarettes e., smoked per day on sm p moking day) and duration (i.e., leng of time in which smo ), gth n oking behavi ior continues versus ceas followin initiation) of smoking after becom s ses ng ming an ever- -smokers. In the n framework, cigarette initiation is depicted by the red arro that den any tran y ows note nsition from nnon- smoking to smoking. Estimates of e-cigarette as a risk f . o es factor for ciggarette initiattion most commonly involve a ratio of thes red lines, such as the l se level of cigaarette initiation among e- - cigarette users as com mpared with those who do not use e- d -cigarettes. Because near all adult combustible tobacco ciga B rly c arette smoke report fir use of ers rst cigarettes before age 26 (IOM, 2015), smokin initiation pertains pri s ng n imarily to yoouth and youung adults. E-cigarette us among youth and youn adults co se ng ould influenc subsequen cigarette ce nt PR REPUBLICA ATION COP UNCO PY: ORRECTED PROOFS D
SECTION III S III-3 initiation in several ways. One scenario is that youth and young adults begin using e-cigarettes and subsequently initiate use of combustible tobacco cigarettes, either through switching or in addition to e-cigarettes. In this scenario, e-cigarette use is associated with cigarette smoking initiation and thus tobacco-related health risks. Another scenario suggests that some portion of youth and young adults who otherwise would have begun smoking combustible tobacco cigarettes would not do so, and would instead begin using e-cigarettes. Here, e-cigarette use would reduce or delay initiation of combustible tobacco cigarette use and could reduce tobacco- related health risks. These potential pathways and corresponding evidence are described further in Chapter 16. E-cigarette use could affect combustible tobacco use among adult smokers through several pathways, with different implications for public health. For example, it is plausible that e-cigarettes promote cessation of combustible tobacco cigarette smoking. The committee defined cigarette cessation as transitions from any combustible tobacco cigarette smoking to non- smoking. By this definition, cessation may involve the outcome of e-cigarette use alone or non- use of both e-cigarettes and combustible tobacco cigarettes. In other words, smokers could either transition completely from combustible tobacco cigarettes to e-cigarette use only or they could start using e-cigarettes in addition to combustible tobacco cigarettes (dual use) for a limited time, and then completely switch to e-cigarette use alone. Smokers could also subsequently quit both combustible tobacco cigarette and e-cigarette use. As the committee previously concluded, e- cigarettes are likely to expose users to fewer and lower levels of potentially toxic substances compared with exposure from combustible tobacco cigarettes and thus to confer lower health risks. Therefore, complete switching from combustible tobacco cigarettes to e-cigarettes would be expected to reduce tobacco-related health risks. E-cigarette users who subsequently stopped using both e-cigarettes and combustible tobacco cigarettes would incur additional benefits. In the framework, combustible tobacco cigarette cessation is depicted by the green arrows that denote any transition from smoking to non-smoking. Estimates for e-cigarettes as a cessation tool most commonly involve a ratio using at least one of these green lines, such as the level of cigarette cessation among active smokers (E1) compared with smokers who recently quit and use e- cigarettes as a replacement (recent members of B1). In these scenarios, e-cigarettes would benefit public health. If, on the other hand, e-cigarettes are not effective cessation aids, e-cigarettes could cause relapse, whereby current e-cigarette use by former or non-active combustible tobacco cigarette users leads these users to transition back to combustible tobacco smoking either alone or concurrently with e-cigarettes. This could occur, for example, if a former smoker uses e- cigarettes under the belief that they are safe and will provide many of the same pleasures as combustible tobacco cigarettes, and follow a path that eventually leads back to active cigarette smoking. In the framework, cigarette relapse is depicted by the purple arrows that denote any transition from non-active to active smoking. As with initiation and cessation, estimates of relapse are based primarily on the ratio of the relevant transition probabilities. In this case, cigarette relapse levels among e-cigarette users are compared with relapse levels among former smokers who do not use e-cigarettes. Among e-cigarette users who relapse, the potential reduction in tobacco-related health risks from a period of temporary switching would likely be minimal. The influence of e-cigarettes on relapse would be especially worrying if e-cigarettes cause relapse among those who otherwise would have remained abstinent from combustible tobacco cigarette smoking, as this would increase both individual and overall public health risk. PREPUBLICATION COPY: UNCORRECTED PROOFS
S III-4 PUBLIC HEALTH CONSEQUENCES OF E-CIGARETTES Discussion of the potential influence of e-cigarettes on cigarette smoking among current and former adult smokers and corresponding evidence can be found in Chapter 17. Finally, current smokers could start using e-cigarettes in addition to combustible tobacco cigarettes (dual use) and persist in using both products concurrently. If use of both products lead to smoking reduction, this could confer health benefits. However, it is also feasible that dual users do not reduce combustible tobacco cigarette use, which could expose them to adverse health effects from the e-cigarettes in addition to those from combustible tobacco use. Discussion and evidence on the influence of concurrent e-cigarette and combustible tobacco cigarette use (dual use) on smoking cessation as well as health outcomes are presented in Chapter 18. In addition to the tobacco use trajectories, the committee considered whether certain factors (or moderators) may strengthen or weaken the association between e-cigarette use and combustible tobacco cigarette use. Much remains unknown about potential moderators, but potentially important moderators that warrant serious consideration include age, motivation of e- cigarette users to smoke or stop smoking, substance vaped in e-cigarettes (e.g., nicotine concentration or flavorings), and whether e-cigarette use is part of a structured cessation program. Information on these moderators is currently scarce, but noted below when available. To understand the overall effect of these different hypothesized pathways among e- cigarette use, combustible tobacco cigarette smoking, and non-use on the U.S. population as a whole, the committee used population-dynamic modeling and presents results of a range of scenarios in Chapter 19. REFERENCES HHS (U.S. Department of Health and Human Services). 2014. The health consequences of smoking-50 years of progress: A report of the Surgeon General. Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Disease Prevention and Health Promotion, Office on Smoking and Health. IOM (Institute of Medicine). 2015. Public health implications of raising the minimum age of legal access to tobacco products. Washington, DC: The National Academies Press. PREPUBLICATION COPY: UNCORRECTED PROOFS