Prospective study of e-cigarette use and respiratory symptoms in adolescents and young adults.

RATIONALE: Electronic cigarette (e-cigarette) aerosol contains volatile aldehydes, including flavourings and oxidant metals with known pulmonary toxicity. OBJECTIVES: To evaluate the associations of e-cigarette use with symptoms of wheeze, bronchitic symptoms and shortness of breath (SOB) across 4 years of prospective data. METHODS: Participants completed questionnaires on respiratory symptoms and past 30-day e-cigarette, cigarette and cannabis use in 2014 (wave 1; N=2094; mean age 17.3 years, SD=0.6 years). Follow-up information was collected in 2015 (wave 2; n=1609), 2017 (wave 3; n=1502) and 2018 (wave 4; n=1637) using online surveys. Mixed-effects logistic regression models evaluated associations of e-cigarette use with respiratory symptoms. MEASUREMENTS AND MAIN RESULTS: Participants were mostly Hispanic white (51.8%) and evenly representative by sex (49.6% female; 50.4% male). Compared with never e-cigarette users, past 30-day e-cigarette users reported increased odds of wheeze (OR 1.81; 95% CI 1.28, 2.56), bronchitic symptoms (OR 2.06; 95% CI 1.58, 2.69) and SOB (OR 1.78; 95% CI 1.23, 2.57), adjusting for study wave, age, sex, race, lifetime asthma diagnosis and parental education. Effect estimates were attenuated (wheeze (OR 1.41; 95% CI 0.99, 2.01), bronchitic symptoms (OR 1.55; 95% CI 1.18, 2.05), SOB (OR 1.48; 95% CI 1.01, 2.18)), after adjusting additionally for current cigarette use, cannabis use and secondhand exposure to e-cigarettes/cigarettes/cannabis. CONCLUSIONS: E-cigarette use in young adults was associated with respiratory symptoms, independent of combustible cannabis and cigarette exposures.

Compliance in Controlled E-cigarette Studies.

INTRODUCTION: E-cigarette studies have found that the use of a variety of flavors and customizable devices results in greater use frequency and user satisfaction. However, standardized research e-cigarettes are being developed as closed systems with limited flavor options, potentially limiting user satisfaction. In this study, we explore protocol compliance in an e-cigarette study using a standardized, assigned device with puff time and duration tracking (controlled e-cigarette) and potential limitations that controlled devices and e-liquids can introduce. METHODS: In a crossover study, 49 young adult e-cigarette users were recruited using convenience sampling and assigned a controlled e-cigarette device and flavored or unflavored e-liquids on standardized protocols. E-cigarette use frequency (number of puffs per day, collected from the device) and serum cotinine levels were obtained at each of three study visits over 3 weeks. The correlation of cotinine and e-cigarette use over the preceding week was calculated at each study visit. RESULTS: Correlation of nicotine intake, as measured by serum cotinine, and puff time, as measured by puffs count and duration from the e-cigarette device, as an indicator of study protocol compliance, substantially declined after the first week of the study and were no longer correlated in the remaining study weeks (R2 = 0.53 and p ≤ .01 in week 1, R2 < 0.5 and p > .05 for remaining weeks). CONCLUSIONS: There is an emerging need for controlled e-cigarette exposures studies, but low compliance in the use of assigned devices and e-liquids may be a limitation that needs to be mitigated in future studies. IMPLICATIONS: This study is the first to analyze compliance with instructions to use a standardized e-cigarette device with puff time and duration tracking (controlled e-cigarette) across all subjects and an assigned e-liquid flavor over a 3-week period. We find that protocol compliance, as measured by correlations between e-cigarette use measures and cotinine levels, was only achieved in the first week of the study and declined thereafter. These findings indicate that the assignment of a study device and instruction to only use the study device with assigned e-liquid flavor may not be sufficient to ensure participant compliance with the study protocol. We suggest that additional measures, including behavioral and biological markers, are needed to ensure sole use of the study e-cigarette and e-liquid and to be able to interpret results from controlled e-cigarette studies.

E-cigarette Product Characteristics and Subsequent Frequency of Cigarette Smoking.

BACKGROUND: There is a dearth of evidence regarding the association of use of electronic cigarettes (e-cigarettes) with certain product characteristics and adolescent and young adult risk of unhealthy tobacco use patterns (eg, frequency of combustible cigarette smoking), which is needed to inform the regulation of e-cigarettes. METHODS: Data were collected via an online survey of participants in the Southern California Children's Health Study from 2015 to 2016 (baseline) and 2016 to 2017 (follow-up) (N = 1312). We evaluated the association of binary categories of 3 nonmutually exclusive characteristics of the e-cigarette used most frequently with the number of cigarettes smoked in the past 30 days at 1-year follow-up. Product characteristics included device (vape pen and/or modifiable electronic cigarette [mod]), use of nicotine in electronic liquid (e-liquid; yes or no), and use for dripping (directly dripping e-liquid onto the device; yes or no). RESULTS: Relative to never e-cigarette users, past-30-day e-cigarette use was associated with greater frequency of past-30-day cigarette smoking at follow-up. Among baseline past-30-day e-cigarette users, participants who used mods (versus vape pens) smoked >6 times as many cigarettes at follow-up (mean: 20.8 vs 1.3 cigarettes; rate ratio = 6.33; 95% confidence interval: 1.64-24.5) after adjustment for sociodemographic characteristics, baseline frequency of cigarette smoking, and number of days of e-cigarette use. After adjustment for device, neither nicotine e-liquid nor dripping were associated with frequency of cigarette smoking. CONCLUSIONS: Baseline mod users (versus vape pen users) smoked more cigarettes in the past 30 days at follow-up. Regulation of e-cigarette device type warrants consideration as a strategy to reduce cigarette smoking among adolescents and young adults who vape.

Risk factors associated with subsequent initiation of cigarettes and e-cigarettes in adolescence: A structural equation modeling approach.

BACKGROUND: Previous youth tobacco research has identified multiple correlated risk factors for initiation of cigarette and e-cigarette use; whether these factors are independently associated with initiation is not known, due to challenges with disentangling the independent effects of these correlated risk factors. METHODS: Students in 11th/12th grade enrolled in the Southern California Children's Health Study were surveyed in 2014 (baseline) and again in 2015 (N = 1553). Structural equation models (SEM) were developed to investigate associations of susceptibility, marketing, and the social environment (as latent factors), and other tobacco use at baseline with cigarette or e-cigarette initiation between baseline and follow-up. Analyses were restricted to baseline never cigarette users (N = 1293) for models evaluating cigarette initiation, and to never e-cigarette users (N = 1197) for models evaluating e-cigarette initiation. RESULTS: In fully-adjusted prospective SEM models, latent factors for cigarette susceptibility, marketing, and the social environment, along with ever e-cigarette use and ever hookah use at baseline were independently associated with cigarette initiation between baseline and follow-up (P < 0.05). Similarly, latent factors for e-cigarette susceptibility, marketing, and the social environment, along with ever hookah use at baseline were associated with e-cigarette initiation between baseline and follow-up (P < 0.05); however, cigarette use at baseline was not associated with e-cigarette initiation in SEM models (P = 0.16). CONCLUSIONS: We identified independent effects of multiple risk factors in SEM models on initiation of cigarettes and e-cigarettes. E-cigarette use was associated with cigarette initiation, but cigarette use was not associated with e-cigarette initiation in fully adjusted models. Research to identify underlying causal mechanisms is warranted.

Past 30-day co-use of tobacco and marijuana products among adolescents and young adults in California.

BACKGROUND: Limited research among adolescents and young adults (AYA) has assessed tobacco and marijuana co-use in light of specific products. We examined the patterns of past 30-day co-use of tobacco and marijuana products, and the product-specific associations among past 30-day use of these substances. METHODS: Data from three school-based convenience samples of California AYA (aged 15-22) (Sample 1 = 3008; Sample 2 = 1419; Sample 3 = 466) were collected during 2016-2017. Proportions of past 30-day co-use of tobacco (e-cigarettes, cigarettes, hookah, cigars) and marijuana (combustible, vaporized, edible, blunt) were estimated. Multivariable logistic regression analyses examined associations between use of each tobacco and marijuana product for individual samples, then the pooled analysis calculated combined ORs. RESULTS: In the three samples, 7.3-11.3% of participants reported past 30-day co-use. Combinations of e-cigarettes or cigarettes and combustible marijuana were the most common co-use patterns. Past 30-day use of e-cigarettes or cigarettes (vs. non-use) increased the odds of past 30-day use of all marijuana products [e-cigarettes: ORs (95%CI) ranging from 2.5 (1.7, 3.2) for edible marijuana to 4.0 (2.8, 5.2) for combustible marijuana; cigarettes: from 3.2 (2.1, 4.2) for vaporized marijuana to 5.5 (3.8, 7.3) for combustible marijuana]. Past 30-day use of hookah or cigars was positively associated with past 30-day use of three of four marijuana products, except for hookah and vaporized marijuana, and for cigars and combustible marijuana. CONCLUSIONS: Given various co-use patterns and significant associations among tobacco and marijuana products, interventions targeting AYA should address co-use across the full spectrum of specific products for both substances.

Evaluating the predictive value of measures of susceptibility to tobacco and alternative tobacco products.

BACKGROUND: The "cigarette susceptibility index" has been adapted for other products, yet, the validity of these adapted measures-particularly among youth who have used other tobacco products-has not been evaluated. METHODS: We used prospective data from the Southern California Children's Health Study to evaluate the association of questionnaire measures assessing susceptibility to e-cigarette, cigarette, hookah and cigar/cigarillo/little cigar use at wave 1 (W1; 11th/12th grade) with subsequent initiation between W1 and W2 (16 months later, N = 1453). We additionally examined whether each effect estimate differed by use of other tobacco products at W1. RESULTS: Odds ratios, attributable risk%, and risk differences for product initiation among susceptible vs. non-susceptible youth were consistently higher among never users of any tobacco product than among youth with any tobacco use history. For example, susceptible (vs. non-susceptible) youth with no prior tobacco use had 3.64 times the odds of subsequent initiation of e-cigarettes (95%CI:2.61,5.09), while among users of another product, susceptible (vs. non-susceptible) youth had 1.95 times the odds of e-cigarette initiation (95%CI:0.98,3.89; p-interaction = 0.016). 60.4% of e-cigarette initiation among never users of any product could be attributed to susceptibility, compared to 19.8% among users of another product. The e-cigarette absolute risk difference between susceptible and non-susceptible youth was 21.9%(15.2,28.6) for never users, vs. 15.4%(0.2,30.7) for users of another product. CONCLUSION: Tobacco product-specific susceptibility associations with initiation of use at W2 were markedly attenuated among prior users of other products, demonstrating reduced utility for these measures among subjects using other products.

Tobacco Retail Licensing and Youth Product Use.

BACKGROUND: Restricting youth access to tobacco is a central feature of US tobacco regulatory policy, but impact of local tobacco retail licensing (TRL) regulation on cigarette smoking rates remains uncertain. Effects of TRL on other tobacco product use and use as adolescents reach the age to legally purchase tobacco products has not been investigated. METHODS: Prevalences of ever and past 30-day cigarette, electronic cigarette (e-cigarette), cigar, and hookah use were assessed in a survey of a cohort of 1553 11th- and 12th-grade adolescents (mean age: 17.3 years); rates of initiation were evaluated 1.5 years later. An American Lung Association (2014) youth access grade was assigned to each of 14 political jurisdictions in which participants lived on the basis of the strength of the local TRL ordinance. RESULTS: At baseline, participants living in 4 jurisdictions with "A" grades (ie, with most restrictive ordinances) had lower odds of ever cigarette use (odds ratio [OR] 0.61; 95% confidence interval [CI] 0.41-0.90) and of past 30-day use (OR 0.51; 95% CI 0.29-0.89) than participants in 10 D- to F-grade jurisdictions. At follow-up at legal age of purchase, lower odds of cigarette use initiation (OR 0.67; 95% CI 0.45-0.99) occurred in jurisdictions with stronger TRL policy. Lower odds of e-cigarette initiation at follow-up (OR 0.74; 95% CI 0.55-0.99) and of initiation with past 30-day use (OR 0.45; 95% CI 0.23-0.90) were also associated with better regulation. CONCLUSIONS: Strong local TRL ordinance may lower rates of cigarette and e-cigarette use among youth and young adults.

Tobacco Marketing and Subsequent Use of Cigarettes, E-Cigarettes, and Hookah in Adolescents.

INTRODUCTION: Tobacco marketing has expanded from cigarettes to other tobacco products through many promotional channels. Marketing exposure is associated with use of that tobacco product. However, it is unclear if marketing for one product leads to subsequent use of other tobacco products. METHODS: This prospective cohort study assessed self-reported marketing exposure for six tobacco products across five marketing channels in 11th and 12th grade students in 2014. Approximately 16 months later, a follow-up survey was conducted online (N = 1553) to assess initiation of cigarettes, electronic cigarettes (e-cigarettes), and hookah. RESULTS: Adolescent never-smokers with frequent exposure to cigarette marketing on the Internet and in stores are more than two times as likely to begin smoking as young adults (Internet OR = 2.98 [95% CI = 1.56 to 5.66]; stores OR = 2.83 [95% CI = 1.23 to 6.50]). Never users of e-cigarettes were significantly more likely to initiate use, if exposed to Internet, store, and outdoor e-cigarette marketing. Never users of hookah were more likely to use hookah after seeing it marketed in stores. Youth exposed to marketing of e-cigarettes, hookah, cigars, smokeless tobacco, and pipe tobacco in stores were two to three times more likely to begin smoking cigarettes even though the marketed products were not cigarettes. CONCLUSIONS: Adolescent exposure to marketing of tobacco products is associated with initiation of those products as young adults. Exposure to marketing for non-cigarette tobacco products is associated with subsequent cigarette smoking, even when the promoted products are not cigarettes. Future research and interventions should consider the influence of marketing from multiple tobacco products on adolescent tobacco use. IMPLICATIONS: Adolescents grow up in a rich media environment with exposure to tobacco marketing in both their homes (eg, through the Internet and television) and their communities (eg, stores and billboards). This prospective study provides evidence that adolescents exposed to tobacco marketing for multiple tobacco products are more likely to subsequently begin using those products and to begin smoking cigarettes even when the marketing they recall is for different tobacco products. Adolescent exposure to tobacco marketing can increase likelihood of cigarette smoking, e-cigarette, and hookah use with potential lifelong health effects.

Electronic Cigarette and Cigarette Social Environments and Ever Use of Each Product: A Prospective Study of Young Adults in Southern California.

BACKGROUND: A supportive youth cigarette social environment, for example, friends' approval of use, leads to cigarette use initiation, and cigarette users develop a more supportive social environment. Whether there is a bidirectional relationship of electronic cigarette (e-cigarette) social environment with e-cigarette use has not been studied. METHODS: Prospective data were collected from 1441 Children's Health Study participants in 2014 (median age = 17.3 years) and at follow-up 1.5 years later. Associations were examined of (1) supportive e-cigarette social environment with subsequent e-cigarette use initiation and (2) baseline e-cigarette use with supportive e-cigarette social environment at follow-up (among those with a nonsupportive baseline social environment). RESULTS: Participants with three to four friends using e-cigarettes at baseline (vs. no friends) had an odds ratio (OR) of 4.08 of subsequent initiation (95% confidence interval [CI] = 1.96 to 8.49); those with best friends who would have a very friendly (vs. unfriendly) reaction to e-cigarette use had an OR of 2.54 of initiation (95% CI = 1.57 to 4.10); and those with someone in the home using e-cigarettes had an OR of 1.94 of initiation (95% CI = 1.19 to 3.15). Participants who had ever used e-cigarettes at baseline developed a supportive social environment at follow-up (OR of 2.06 of having any friends who used e-cigarettes [95% CI = 1.29 to 3.30] and OR of 2.33 of having friends who were friendly toward use [95% CI = 1.32 to 4.11]). Similar bidirectional associations were observed between ever cigarette use and a supportive cigarette social environment. CONCLUSIONS: The bidirectional relationship between a supportive e-cigarette social environment and ever use of e-cigarettes was similar to that previously observed between cigarette social environment and cigarette use. IMPLICATIONS: Disrupting the social acceptability of youth e-cigarette use merits consideration as a strategy for preventing initiation of e-cigarette use, just as the social denormalization of cigarette use has proven to be effective in preventing cigarette initiation.

The impact of local regulation on reasons for electronic cigarette use among Southern California young adults.

OBJECTIVE: Tobacco control policies have decreased tobacco use among youth and young adults. We aimed to identify whether specific local tobacco retail licensing ordinances were associated with reasons for e-cigarette use, in order to examine whether strong local policies may reduce e-cigarette initiation rates by influencing the appeal of these products. METHODS: Online questionnaires were completed by Southern California Children's Health Study participants in 2015-2016 (mean age = 18.9 years). Those who had ever used an e-cigarette (N = 614) were asked about reasons for use; additional data were collected on local jurisdiction tobacco sales policy, friends' attitudes toward e-cigarette use, e-cigarette characteristics (level of nicotine, flavorings), and history of tobacco use. Multivariate logistic regression models evaluated associations of each factor with reasons for e-cigarette use, adjusting for gender, ethnicity, highest parental education, tobacco use history and with a random effect of jurisdiction. RESULTS: The top reason for e-cigarette use was "They come in flavors I like" (56.6%). Using e-cigarettes to quit smoking was uncommon (12.8%). Participants in jurisdictions with weaker tobacco retail licensing ordinances were more likely to report use of e-cigarettes because they are less harmful than cigarettes (50.1% vs. 36.2%), more acceptable to non-tobacco users (38% vs. 25%), and because they can use e-cigarettes in places where smoking is prohibited (30.7% vs. 18.3%; all p < .05). CONCLUSION: Targeted policy to enforce a strong regulatory environment that denormalizes e-cigarette use, conveys the adverse impact of e-cigarettes, and restricts use in public places may reduce e-cigarette use among adolescents and young adults.

Association between AXL promoter methylation and lung function growth during adolescence.

AXL is one of the TAM (TYRO3, AXL and MERTK) receptor tyrosine kinases and may be involved in airway inflammation. Little is known about how epigenetic changes in AXL may affect lung development during adolescence. We investigated the association between AXL DNA methylation at birth and lung function growth from 10 to 18 years of age in 923 subjects from the Children's Health Study (CHS). DNA methylation from newborn bloodspots was measured at multiple CpG loci across the regulatory regions of AXL using Pyrosequencing. Linear spline mixed-effects models were fitted to assess the association between DNA methylation and 8-year lung function growth. Findings were evaluated for replication in a separate population of 237 CHS subjects using methylation data from the Illumina HumanMethylation450 (HM450) array when possible. A 5% higher average methylation level of the AXL promoter region at birth was associated with a 48.4 ml decrease in mean FEV1 growth from 10 to 18 years of age in the primary study population (95% CI: -100.2, 3.4), and a 53.9 ml decrease in mean FEV1 growth from 11 to 15 years of age in the replication population (95% CI: -104.3, -3.5). One CpG locus in the promoter region, cg10564498, was significantly associated with decreased growth in FEV1, FVC and MMEF from 10 to 18 years of age and the negative associations were observed in a similar age range in the replication population. These findings suggest a potential association between AXL promoter methylation at birth and lower lung function growth during adolescence.

Talking about tobacco on Twitter is associated with tobacco product use.

Tobacco-related content appears on social media in the form of advertising and messages by individuals. However, little is known about associations between posting social media messages and tobacco product use among adolescents and young adults. Self-reports of tobacco product use were obtained from the Children's Health Study of young adults in Southern California. Among the 1486 respondents in the most recent wave of the cohort (2016-2017), 284 provided tobacco product use data and their Twitter user names to access publicly available Twitter account data (mean age = 20.1 yrs. (SD = 0.6), 54% female, 49% Hispanic). We obtained the tweets that those respondents posted on Twitter, searched the tweets for 14 nicotine- and tobacco-related keywords, and coded these statements as positive or negative/neutral. Logistic regression analyses were conducted to determine whether respondents who posted positive tobacco-related tweets were more likely to report tobacco product use, relative to those who did not post any positive tobacco-related tweets. Respondents who posted any positive messages about tobacco had significantly higher odds of reporting past month use of cigarettes (OR = 3.15, 95% CI = 1.36, 7.30) and any tobacco product (OR = 2.41, 95% CI = 1.16, 5.01), relative to respondents who did not post about tobacco. This is the first study to establish an empirical link between adolescents' and young adults' tobacco-related Twitter activity and their tobacco product use. Health communications about the risks of tobacco use could target adolescents who post positive messages about tobacco products on Twitter.

Performance of cigarette susceptibility index among e-cigarette and hookah users.

OBJECTIVE: Susceptibility to cigarette smoking has been used since the mid-1990s as a measure to identify youth at risk of cigarette initiation. However, it is unclear how well this measure predicts future smoking among electronic (e-)cigarette or hookah users, or among those in tobacco-friendly social environments. METHODS: We used prospective data from the Southern California Children's Health Study to evaluate the performance (sensitivity, specificity, predictive value) of a composite index assessing susceptibility to smoking, and to evaluate whether performance of the measure differed by use of e-cigarettes or hookah, or immersion in a tobacco-friendly social environment. Susceptibility to cigarette smoking was measured in 11th/12th grade (2014) among never cigarette-smokers (N=1266); follow-up data on smoking initiation were obtained approximately 16 months later. RESULTS: Overall, 16.4% of youth initiated smoking between baseline and follow-up. The sensitivity of the susceptibility to smoking index was low (46.4%), and specificity was high (79.0%). No difference in sensitivity was observed by baseline e-cigarette use; specificity was higher among never e- cigarette users. Differences in negative predictive value (NPV) and positive predictive value (PPV) were also observed by baseline e-cigarette and hookah use. Specificity was generally lower, and sensitivity was generally higher for those in tobacco-friendly social environments. CONCLUSIONS: Our findings suggest that use of the susceptibility to smoking index in cross-sectional studies of older adolescents to identify those likely to begin smoking may be inappropriate for those using alternative tobacco products (e.g., e-cigarettes or hookah).

Perceived stress and poly-tobacco product use across adolescence: Patterns of association and gender differences.

Perceived stress-an endophenotype indicative of the tendency to appraise stress as frequent, unpredictable and unmanageable-is associated with adolescent cigarette smoking. It is unclear whether this association: (1) extends to alternative tobacco products, like electronic cigarettes and hookah (tobacco water pipe), which are increasingly popular among youth, and (2) differs by gender. In this report, data were drawn from a population-based longitudinal cohort of youth in Southern California. Perceived stress was assessed at baseline (7th or 8th grade; 2010). Electronic cigarette, hookah, combustible cigarette, and cigar use were assessed at a 4-year follow-up (11th or 12th grade; 2014). After adjusting for confounders, polytomous logistic regressions showed that a standardized baseline perceived stress score (M = 0, SD = 1) predicted electronic cigarette, hookah, combustible cigarette, and cigar use and a poly-tobacco use index at the 4-year follow-up in the overall sample. Interactions between perceived stress and gender were also observed (Interaction Ps < 0.05), which demonstrated that the association of perceived stress with tobacco product use and poly-use were stronger in females (ORs for current use range: 1.47 to 1.72) than males (ORs range: 0.93 to 1.31). Adjusting for baseline perceived stress, the change in perceived stress from baseline to follow-up was also positively associated with use and poly-use of most tobacco products in females and in males to some extent. In the current era in which teen use of alternative tobacco products is increasingly common, adolescent tobacco use and poly-use research and prevention strategies should address gender-specific origins of tobacco product use risk and consider perceived stress and other emotional endophenotypes in such risk pathways.

Electronic Cigarette Use and Respiratory Symptoms in Adolescents.

RATIONALE: Rates of adolescent electronic (e-) cigarette use are increasing, but there has been little study of the chronic effects of use. Components of e-cigarette aerosol have known pulmonary toxicity. OBJECTIVES: To investigate the associations of e-cigarette use with chronic bronchitis symptoms and wheeze in an adolescent population. METHODS: Associations of self-reported use of e-cigarettes with chronic bronchitic symptoms (chronic cough, phlegm, or bronchitis) and of wheeze in the previous 12 months were examined in 2,086 Southern California Children's Health Study participants completing questionnaires in 11th and 12th grade in 2014. MEASUREMENTS AND MAIN RESULTS: Ever e-cigarette use was reported by 502 (24.0%), of whom 201 (9.6%) used e-cigarettes during the last 30 days (current users). Risk of bronchitic symptoms was increased by almost twofold among past users (odds ratio [OR], 1.85; 95% confidence interval [CI], 1.37-2.49), compared with never-users, and by 2.02-fold (95% CI, 1.42-2.88) among current users. Risk increased with frequency of current use (OR, 1.66; 95% CI, 1.02-2.68) for 1-2 days and 2.52 (95% CI, 1.56-4.08) for 3 or more days in past 30 days compared with never-users. Associations were attenuated by adjustment for lifetime number of cigarettes smoked and secondhand smoke exposure. However, risk of bronchitic symptoms among past e-cigarette users remained elevated after adjustment for relevant potential confounders and was also observed among never-cigarette users (OR, 1.70; 95% CI, 1.11-2.59). There were no statistically significant associations of e-cigarette use with wheeze after adjustment for cigarette use. CONCLUSIONS: Adolescent e-cigarette users had increased rates of chronic bronchitic symptoms. Further investigation is needed to determine the long-term effects of e-cigarettes on respiratory health.

E-cigarettes, Cigarettes, and the Prevalence of Adolescent Tobacco Use.

BACKGROUND: Adolescent e-cigarette use has increased rapidly in recent years, but it is unclear whether e-cigarettes are merely substituting for cigarettes or whether e-cigarettes are being used by those who would not otherwise have smoked. To understand the role of e-cigarettes in overall tobacco product use, we examine prevalence rates from Southern California adolescents over 2 decades. METHODS: The Children's Health Study is a longitudinal study of cohorts reaching 12th grade in 1995, 1998, 2001, 2004, and 2014. Cohorts were enrolled from entire classrooms in schools in selected communities and followed prospectively through completion of secondary school. Analyses used data from grades 11 and 12 of each cohort (N = 5490). RESULTS: Among 12th-grade students, the combined adjusted prevalence of current cigarette or e-cigarette use in 2014 was 13.7%. This was substantially greater than the 9.0% adjusted prevalence of current cigarette use in 2004, before e-cigarettes were available (P = .003) and only slightly less than the 14.7% adjusted prevalence of smoking in 2001 (P = .54). Similar patterns were observed for prevalence rates in 11th grade, for rates of ever use, and among both male and female adolescents and both Hispanic and Non-Hispanic White adolescents. CONCLUSIONS: Smoking prevalence among Southern California adolescents has declined over 2 decades, but the high prevalence of combined e-cigarette or cigarette use in 2014, compared with historical Southern California smoking prevalence, suggests that e-cigarettes are not merely substituting for cigarettes and indicates that e-cigarette use is occurring in adolescents who would not otherwise have used tobacco products.

E-Cigarettes and Future Cigarette Use.

BACKGROUND: There has been little research examining whether e-cigarette use increases the risk of cigarette initiation among adolescents in the transition to adulthood when the sale of cigarettes becomes legal. METHODS: The Children's Health Study is a prospectively followed cohort in Southern California. Data on e-cigarette use were collected in 11th and 12th grade (mean age = 17.4); follow-up data on tobacco product use were collected an average of 16 months later from never-smoking e-cigarette users at initial evaluation (n = 146) and from a sample of never-smoking, never e-cigarette users (n = 152) frequency matched to e-cigarette users on gender, ethnicity, and grade. RESULTS: Cigarette initiation during follow-up was reported by 40.4% of e-cigarette users (n = 59) and 10.5% of never users (n = 16). E-cigarette users had 6.17 times (95% confidence interval: 3.30-11.6) the odds of initiating cigarettes as never e-cigarette users. Results were robust to adjustment for potential confounders and in analyses restricted to never users of any combustible tobacco product. Associations were stronger in adolescents with no intention of smoking at initial evaluation. E-cigarette users were also more likely to initiate use of any combustible product (odds ratio = 4.98; 95% confidence interval: 2.37-10.4), including hookah, cigars, or pipes. CONCLUSIONS: E-cigarette use in never-smoking youth may increase risk of subsequent initiation of cigarettes and other combustible products during the transition to adulthood when the purchase of tobacco products becomes legal. Stronger associations in participants with no intention of smoking suggests that e-cigarette use was not simply a marker for individuals who would have gone on to smoke regardless of e-cigarette use.

The E-cigarette Social Environment, E-cigarette Use, and Susceptibility to Cigarette Smoking.

PURPOSE: One concern regarding the recent increase in adolescent e-cigarette use is the possibility that electronic (e-) cigarettes may be used by those who might not otherwise have used cigarettes, and that dual use, or transition to cigarette use alone, may follow. METHODS: Questionnaire data were obtained in 2014 from 11th/12th grade students attending schools in 12 communities included in the Southern California Children's Health Study. We evaluated the cross-sectional association between e-cigarette use, the social environment (family and friends' use and approval of e-cigarettes and cigarettes), and susceptibility to future cigarette use among never cigarette smokers (N = 1,694), using previously validated measures based on reported absence of a definitive commitment not to smoke. RESULTS: Among adolescents who had never used cigarettes, 31.8% of past e-cigarette users and 34.6% of current (past 30-day) e-cigarette users indicated susceptibility to cigarette use, compared with 21.0% of never e-cigarette users. The odds of indicating susceptibility to cigarette use were two times higher for current e-cigarette users compared with never users (odds ratio = 1.97; 95% confidence interval: 1.21-3.22). A social environment favorable to e-cigarettes (friends' use of and positive attitudes toward the use of e-cigarettes) was also associated with greater likelihood of susceptibility to cigarette use, independent of an individual's e-cigarette use. CONCLUSIONS: E-cigarette use in adolescence, and a pro-e-cigarette social environment, may put adolescents at risk for future use of cigarettes. E-cigarettes may contribute to subsequent cigarette use via nicotine addiction or social normalization of smoking behaviors.

Patterns of Alternative Tobacco Product Use: Emergence of Hookah and E-cigarettes as Preferred Products Amongst Youth.

PURPOSE: There is a growing public health concern related to the rapid increase in the use of multiple tobacco products among adolescents. This study examined patterns of adolescent use of cigarettes, e-cigarettes, cigars/cigarillo, hookah/waterpipe, and smokeless/dip/chewing tobacco in a population of southern California adolescents. METHODS: Data from 2,097 11th- and 12th-grade participants in the Southern California Children's Health Study were collected via self-report in 2014. Study participants were asked about lifetime and current (past 30 days) use of cigarettes, cigars/cigarillos/little cigars, e-cigarettes, hookah/waterpipe, and smokeless/dip/chewing tobacco. Latent class analysis (LCA) was used to identify patterns of tobacco use. RESULTS: Hookah/waterpipe tobacco use had the highest current prevalence (10.7%) followed by e-cigarettes (9.6%). The prevalence of use of smokeless/dip/chewing tobacco was lowest, with 2.2% of adolescents reporting current use. The LCA suggested four distinct classes, comprising nonusers (72.3% of the sample), polytobacco experimenters (13.9%), e-cigarette/hookah users (8.2%), and polytobacco users (5.6%). Multinomial logistic regression based on these four classes found that males had double the odds to be polytobacco users relative to nonusers compared to females (odds ratio, 2.3; 95% confidence interval, 1.26-4.25). CONCLUSIONS: By identifying naturally occurring configurations of tobacco product use in teens, these findings may be useful to practitioners and policymakers to identify the need for tobacco control interventions that address specific tobacco products and particular combinations of polytobacco use. LCA can be used to identify segments of the population overrepresented among certain tobacco use classes (e.g., boys) that may benefit most from targeted polyproduct intervention approaches.

Psychosocial Factors Associated With Adolescent Electronic Cigarette and Cigarette Use.

BACKGROUND: Use of electronic cigarettes (e-cigarettes) among adolescents has increased since their introduction into the US market in 2007. Little is known about the role of e-cigarette psychosocial factors on risk of e-cigarette or cigarette use in adolescence. METHODS: Information on e-cigarette and cigarette psychosocial factors (use and attitudes about use in the home and among friends) was collected from 11th- and 12th-grade participants in the Southern California Children's Health Study during the spring of 2014. RESULTS: Of 2084 participants, 499 (24.0%) had used an e-cigarette, including 200 (9.6%) current users (past 30 days); 390 participants (18.7%) had smoked a combustible cigarette, and 119 (5.7%) were current cigarette smokers. Cigarette and e-cigarette use were correlated. Nevertheless, 40.5% (n = 81) of current e-cigarette users had never smoked a cigarette. Psychosocial factors (home use of each product, friends' use of and positive attitudes toward e-cigarettes and cigarettes) and participant perception of the harm of e-cigarettes were strongly positively associated both with e-cigarette and cigarette use. Most youth who reported e-cigarette use had friends who used e-cigarettes, and almost half of current users reported that they did not believe there were health risks associated with e-cigarette use. CONCLUSIONS: Longitudinal studies of adolescents are needed to determine whether the strong association of e-cigarette psychosocial factors with both e-cigarette and cigarette use will lead to increased cigarette use or dual use of cigarettes and e-cigarettes, or whether e-cigarettes will serve as a gateway to cigarette use.