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Importance: The prevalence of electronic nicotine delivery systems (ENDS) use, including e-cigarettes, among US young adults (YAs) has raised questions about how these products may affect future tobacco and nicotine use among YAs. Given this prevalence and that young adulthood is a critical period for the establishment of tobacco and nicotine use, it is important to consider the association between ENDS use and cigarette smoking specifically in this age group., Objective: To examine whether ENDS use frequency or intensity is associated with changes in cigarette smoking among US YA ever smokers during 1 year., Design, Setting, and Participants: This cohort study used 3 waves of data (2013-2014, 2014-2015, and 2015-2016) from the Population Assessment of Tobacco and Health (PATH) Study, an ongoing longitudinal cohort study of adults and youth. Unweighted 1:6 propensity score matching was used to match participants on wave 1 risk factors for ENDS use at wave 2. The changes in smoking between wave 2 and wave 3 were assessed using the matched sample. In total, 1096 ENDS-naive, ever cigarette-smoking YAs (18-24 years of age) at wave 1 who participated in wave 2 and wave 3 and who had complete data in the PATH Study were included in the analyses, which were conducted from August 2018 to October 2019., Exposures: Never ENDS use (n = 987), any previous 30-day ENDS use (n = 109), 1 to 5 days of ENDS use in the previous 30 days (n = 75), and 6 or more days ENDS use in the previous 30 days at wave 2 (n = 34)., Main Outcomes and Measures: The analytic sample was selected using multiple variables based on peer-reviewed literature supporting associations with ENDS use. The main outcomes-changes in cigarette smoking behavior between wave 2 and wave 3-were defined using 2 measures: (1) change in smoking frequency, defined as the number of smoking days in the previous 30 days at wave 3 vs wave 2, and (2) change in smoking intensity, defined as the number smoking days in the previous 30 days multiplied by the mean number of cigarettes consumed on smoking days at wave 3 vs wave 2., Results: The present cohort analyses included 1096 YA ever smokers who were ENDS naive at wave 1. The majority of the sample were women (609 [55.6%]) and White individuals (698 [63.7%]), and the mean (SD) age was 21.4 (1.9) years. In wave 1, 161 YAs (14.7%) were daily smokers in the previous 30 days. After propensity score matching, no statistically significant associations were observed between any definition of wave 2 ENDS use and changes in either the frequency or intensity of smoking at wave 3., Conclusions and Relevance: In this cohort study of US YA ever smokers, ENDS use was not associated with either decreased or increased cigarette smoking during a 1-year period. However, it is possible that the rapidly evolving marketplace of vaping products may lead to different trajectories of YA cigarette and ENDS use in the future.

Importance: Use of electronic cigarettes (e-cigarettes) is increasing. Measures of exposure to known tobacco-related toxicants among e-cigarette users will inform potential health risks to individual product users., Objectives: To estimate concentrations of tobacco-related toxicants among e-cigarette users and compare these biomarker concentrations with those observed in combustible cigarette users, dual users, and never tobacco users., Design, Setting, and Participants: A population-based, longitudinal cohort study was conducted in the United States in 2013-2014. Cross-sectional analysis was performed between November 4, 2016, and October 5, 2017, of biomarkers of exposure to tobacco-related toxicants collected by the Population Assessment of Tobacco and Health Study. Participants included adults who provided a urine sample and data on tobacco use (N = 5105)., Exposures: The primary exposure was tobacco use, including current exclusive e-cigarette users (n = 247), current exclusive cigarette smokers (n = 2411), and users of both products (dual users) (n = 792) compared with never tobacco users (n = 1655)., Main Outcomes and Measures: Geometric mean concentrations of 50 individual biomarkers from 5 major classes of tobacco product constituents were measured: nicotine, tobacco-specific nitrosamines (TSNAs), metals, polycyclic aromatic hydrocarbons (PAHs), and volatile organic compounds (VOCs)., Results: Of the 5105 participants, most were aged 35 to 54 years (weighted percentage, 38%; 95% CI, 35%-40%), women (60%; 95% CI, 59%-62%), and non-Hispanic white (61%; 95% CI, 58%-64%). Compared with exclusive e-cigarette users, never users had 19% to 81% significantly lower concentrations of biomarkers of exposure to nicotine, TSNAs, some metals (eg, cadmium and lead), and some VOCs (including acrylonitrile). Exclusive e-cigarette users showed 10% to 98% significantly lower concentrations of biomarkers of exposure, including TSNAs, PAHs, most VOCs, and nicotine, compared with exclusive cigarette smokers; concentrations were comparable for metals and 3 VOCs. Exclusive cigarette users showed 10% to 36% lower concentrations of several biomarkers than dual users. Frequency of cigarette use among dual users was positively correlated with nicotine and toxicant exposure., Conclusions and Relevance: Exclusive use of e-cigarettes appears to result in measurable exposure to known tobacco-related toxicants, generally at lower levels than cigarette smoking. Toxicant exposure is greatest among dual users, and frequency of combustible cigarette use is positively correlated with tobacco toxicant concentration. These findings provide evidence that using combusted tobacco cigarettes alone or in combination with e-cigarettes is associated with higher concentrations of potentially harmful tobacco constituents in comparison with using e-cigarettes alone.