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The association between heated tobacco product use and cigarette cessation outcomes among youth smokers: A prospective cohort study

Published:August 14, 2021DOI:https://doi.org/10.1016/j.jsat.2021.108599

      Highlights

      • Youth HTP users were less likely to abstain from cigarette use than their non-HTP-using comparators.
      • HTPs were insufficient to be used as tools to aid smoking cessation for youth smokers.
      • No significant differences in cigarette consumption reduction between the youth HTP users and their non-HTP-using comparators.
      • No significant differences in cigarette quit attempts between the youth HTP users and their non-HTP-using comparators.
      • No significant differences in readiness level to quit between the youth HTP users and their non-HTP-using comparators.
      • After quitting cigarettes, youth HTP users were more likely to relapse than their non-HTP-using comparators.

      Abstract

      Introduction

      The U.S. Food and Drug Administration authorized the marketing of heated tobacco products (HTPs) with modified-risk information for adults on July 7, 2020. However, the effects of HTP use on cigarette cessation among youth smokers remain unclear. This study aimed to explore the association of HTP use with cigarette abstinence and cessation outcomes among youth smokers in Hong Kong who were willing to receive telephone counseling for smoking cessation.

      Methods

      This prospective cohort study included youth smokers aged ≤25 years who were enrolled in the Hong Kong Youth Quitline service. From December 1, 2016, to September 30, 2019, this study identified as HTP users 106 youth cigarette smokers who reported using HTPs on at least 1 of the past 30 days at enrollment, and identified as non-HTP users 473 smokers who reported smoking at least one conventional cigarette in the past 30 days and never using HTPs. The participants received follow-ups at 1 week and 1-, 3-, and 6-months postenrollment. The primary outcome was self-reported 7-day point prevalence of cigarette abstinence (PPA) at the 6-month follow-up. Secondary outcomes included reduction in cigarette smoking (excluding quitters), the number of cessation attempts, and the level of readiness to quit.

      Results

      The self-reported 7-day PPA was statistically significantly lower among HTP users than among non-HTP users after 6 months (19.0% vs. 34.2%; p = 0.009), with an adjusted relative risk of 0.47 (95% confidence interval: 0.24–0.91; p = 0.03). The study identified no significant differences in secondary outcomes between the two groups.

      Conclusions

      Youth HTP users were less likely to abstain from tobacco use than their non-HTP-using counterparts. These results suggest that HTPs should not be promoted as smoking cessation or reduction aids among the youth population.

      Abbreviations:

      HTP (Heated Tobacco Product), PPA (Point Prevalence of cigarette Abstinence), RR (Relative Risk), CI (Confidence Interval), SD (Standard Deviation)

      Keywords

      1. Introduction

      Heated tobacco products (HTPs), of which the best-known one is IQOS, were first released in Japan, Italy, and Switzerland in 2014; they are now available in 49 countries (

      World Health Organization. (2018). Heated Tobacco Products (HTPS): Market monitoring information sheet (No. WHO/NMH/PND/18.7). World Health Organization. https://apps.who.int/iris/bitstream/handle/10665/273459/ WHO-NMH-PND-18.7-eng.pdf?ua=1.

      ). In Japan, the proportion of individuals under 30 who use HTPs increased rapidly from 0.9% in 2015 to 4.4% in 2017, with 7.8% of the Japanese population under 30 reporting ever using HTPs in 2017 (
      • Tabuchi T.
      • Gallus S.
      • Shinozaki T.
      • Nakaya T.
      • Kunugita N.
      • Colwell B.
      Heat-not-burn tobacco product use in Japan: Its prevalence, predictors and perceived symptoms from exposure to secondhand heat-not-burn tobacco aerosol.
      ). The prevalence of ever HTP use among Korean adolescents aged 13–18 years was 2.9% only 1 year after the release of HTPs in Korea (
      • Kang S.Y.
      • Lee S.
      • Cho H.J.
      Prevalence and predictors of heated tobacco product use and its relationship with attempts to quit cigarette smoking among Korean adolescents.
      ). In Hong Kong, a region with a low prevalence of cigarette smoking (10.2% in 2019) (

      Census and Statistics Department. (2019, June 8). Thematic household survey report no. 70: Pattern of smoking. https://www.statistics.gov.hk/pub/B11302702020XXXXB0100.pdf.

      ), HTPs have not been formally released in the market. However, HTP components, including electronic devices, tobacco sticks, and other accessories, can be readily obtained online (
      • Wu Y.
      Perception and use of new tobacco products among youth and adults in Hong Kong.
      ). A population-based cross-sectional study in Hong Kong reported ever HTP use in approximately 20% of people under 30 years old (
      • Wu Y.S.
      • Wang M.P.
      • Ho S.Y.
      • Li H.
      • Cheung Y.
      • Tabuchi T.
      • Kwong A.C.
      • Lai V.
      • Lam T.H.
      Heated tobacco products use in Chinese adults in Hong Kong: A population-based cross-sectional study.
      ). Moreover, research has noted that HTP use is becoming increasingly popular among youth (
      • Ratajczak A.
      • Jankowski P.
      • Strus P.
      • Feleszko W.
      Heat not burn tobacco product-a new global trend: Impact of heat-not-burn tobacco products on public health, a systematic review.
      ).
      The U.S. Food and Drug Administration (FDA) authorized the marketing of HTPs with modified-risk information on July 7, 2020 (

      Center for Tobacco Products. (2020, July 7). Addendum to FDA briefing document. Philip Morris products S.A. Modified Risk Tobacco Product (MRTP) applications. https://www.fda.gov/tobacco-products/advertising-and-promotion/ philip-morris-products-sa-modified-risk-tobacco-product-mrtp-applications.

      ), under the assumption that HTP use could help addicted adult smokers to transition away from using combusted cigarettes and reduce their exposure to harmful chemicals. However, the modified risk status only works in the case of tobacco-addicted adults who completely switch from conventional cigarette use to HTPs (

      Center for Tobacco Products. (2020, July 7). Addendum to FDA briefing document. Philip Morris products S.A. Modified Risk Tobacco Product (MRTP) applications. https://www.fda.gov/tobacco-products/advertising-and-promotion/ philip-morris-products-sa-modified-risk-tobacco-product-mrtp-applications.

      ), which is not the common use pattern among most HTP users (
      • Hwang J.H.
      • Ryu D.H.
      • Park S.W.
      Heated tobacco products: Cigarette complements, not substitutes.
      ). Additionally, FDA authorization does not mean that the FDA has approved HTPs as safe cessation devices. Studies have reported that HTPs are not effective cessation devices among adult smokers compared to other cessation aids, e.g., nicotine replacement products (
      • Chen R.
      • Pierce J.P.
      • Leas E.C.
      • White M.M.
      • Kealey S.
      • Strong D.R.
      • Trinidad D.R.
      • Benmarhnia T.
      • Messer K.
      Use of electronic cigarettes to aid long-term smoking cessation in the United States: Prospective evidence from the PATH cohort study.
      ;
      • Kim J.
      • Lee S.
      • Kimm H.
      • Lee J.A.
      • Lee C.M.
      • Cho H.J.
      Heated tobacco product use and its relationship to quitting combustible cigarettes in Korean adults.
      ). Previous studies have even reported that approximately 78% of youth smokers who use HTPs become dual, or even triple, tobacco product users, rather than transitioning away from conventional cigarettes to exclusive HTP use (
      • Hwang J.H.
      • Ryu D.H.
      • Park S.W.
      Heated tobacco products: Cigarette complements, not substitutes.
      ;
      • Kim J.
      • Yu H.
      • Lee S.
      • Paek Y.J.
      Awareness, experience and prevalence of heated tobacco product, IQOS, among young Korean adults.
      ). Despite studies finding that HTP users were more likely to have attempted to quit cigarette smoking than those who had never used HTPs (
      • Kang S.Y.
      • Lee S.
      • Cho H.J.
      Prevalence and predictors of heated tobacco product use and its relationship with attempts to quit cigarette smoking among Korean adolescents.
      ), the role of HTP use in cigarette cessation among youth smokers remains unclear (
      • Ratajczak A.
      • Jankowski P.
      • Strus P.
      • Feleszko W.
      Heat not burn tobacco product-a new global trend: Impact of heat-not-burn tobacco products on public health, a systematic review.
      ). Most previous studies have investigated the relationship between HTP use and smoking cessation outcomes among youth using cross-sectional approaches, and the findings have been broadly inconclusive (
      • Czoli C.D.
      • White C.M.
      • Reid J.L.
      • OConnor R.J.
      • Hammond D.
      Awareness and interest in IQOS heated tobacco products among youth in Canada, England and the USA.
      ;
      • Kang S.Y.
      • Lee S.
      • Cho H.J.
      Prevalence and predictors of heated tobacco product use and its relationship with attempts to quit cigarette smoking among Korean adolescents.
      ;
      • McKelvey K.
      • Baiocchi M.
      • Halpern-Felsher B.
      PMI's heated tobacco products marketing claims of reduced risk and reduced exposure may entice youth to try and continue using these products.
      ;
      • Ratajczak A.
      • Jankowski P.
      • Strus P.
      • Feleszko W.
      Heat not burn tobacco product-a new global trend: Impact of heat-not-burn tobacco products on public health, a systematic review.
      ). Moreover, according to our literature search, little longitudinal evidence is available regarding this relationship. Thus, this study explored the association between HTP use and cigarette abstinence and cessation in a prospective cohort of youth smokers aged 25 years or younger in Hong Kong who intended to quit smoking.

      2. Material and methods

      2.1 Study design and data sources

      The participants in this prospective cohort study were users of the Hong Kong Youth Quitline service. The reporting of this study follows the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines for cohort studies (
      • von Elm E.
      • Altman D.G.
      • Egger M.
      • Pocock S.J.
      • Gøtzsche P.C.
      • Vandenbroucke J.P.
      • Initiative S.T.R.O.B.E.
      The strengthening the reporting of observational studies in epidemiology (STROBE) statement: Guidelines for reporting observational studies.
      ). The Hong Kong Youth Quitline service is funded by the Department of Health and has been operated by the Smoking Cessation Research Team from the School of Nursing, The University of Hong Kong, since 2005. Details of the program have been reported elsewhere (
      • Li W.
      • Chan S.
      • Wang M.P.
      • Ho K.Y.
      • Cheung Y.
      • Chan V.
      • Lam T.H.
      An evaluation of the youth quitline service young Hong Kong smokers.
      ).

      2.2 Setting and participants

      Trained research assistants screened individuals who directly contacted the Youth Quitline, who were actively recruited to the service via schools and the community, and who were referred from other institutions via a screen sheet. Individuals were eligible for the Youth Quitline service if they 1) were aged ≤25 years; 2) had smoked at least one tobacco product of any kind in the past 30 days; 3) spoke Cantonese; and 4) were willing to receive telephone counseling to support smoking cessation. This study excluded youth smokers who were psychologically or physically unable to communicate or who were participating in other smoking cessation research programs or services.
      This study screened for eligibility youth smokers who enrolled in the Youth Quitline from December 2016 to September 2019. The study identified youth cigarette smokers who reported dual use of HTPs and conventional cigarettes on at least 1 of the past 30 days as HTP users, and identified those who reported having smoked at least one conventional cigarette in the past 30 days and never using HTPs at enrollment as non-HTP users. After excluding those who reported using other tobacco (e.g. E-cigarette, shisha, etc.) products in the past 30 days at baseline, the analytical cohort included 579 youth smokers.

      2.3 Smoking cessation service

      To motivate youth smokers to quit, the trained peer counselors at the Youth Quitline service provided smoking cessation counseling to the recruited smokers according to the “5As” model: 1) Asking about tobacco use to assess the participants' nicotine dependence level and the number of previous cessation attempts; 2) using a risk communication approach and explaining the negative health effects of active and passive smoking and the benefits of quitting smoking, thereby Advising them to quit smoking; 3) Assessing their willingness to quit; 4) designing an individualized cessation plan to Assist a quit attempt with a prospective quit date, as a short-term goal, thereby strengthening their self-efficacy in quitting by increasing their perceived competency in coping with withdrawal symptoms; and 5) Arranging for telephone follow-ups.

      2.4 Instruments

      This study used a well-validated structured questionnaire to collect data (
      • Abdullah A.S.
      • Ho W.W.
      What Chinese adolescents think about quitting smoking: A qualitative study.
      ;
      • Abdullah A.S.
      • Lam T.H.
      • Chan S.S.
      • Hedley A.J.
      Smoking cessation among chinese young smokers: does gender and age difference matters and what are the predictors?.
      ). The baseline questionnaire covered: 1) smoking profile, including the types and number of tobacco products used, age at smoking initiation, number of years of smoking, and level of nicotine dependence, in addition to HTP use within the previous 30 days, reasons for HTP use initiation, and the initiation order of HTP and cigarette use (for HTP users); 2) past cigarette quit attempts lasting more than 24 h within the past 12 months; 3) level of readiness to quit (preparedness to quit cigarettes within 1 month vs. after 1 month); 4) perspectives on the importance of, difficulty of, and confidence in quitting smoking; 5) attitudes towards HTPs; and 6) demographic characteristics. The study assessed nicotine dependence levels using the Fagerström Test for Nicotine Dependence; the internal consistency for the Chinese version of this instrument is 0.74 (
      • Huang C.L.
      • Lin H.H.
      • Wang H.H.
      Psychometric evaluation of the Chinese version of the fagerstrom tolerance questionnaire as a measure of cigarette dependence.
      ). We measured the perspectives on the importance of, difficulty of, and confidence in quitting smoking by a single-item 11-point Likert-type scale ranging from 0 (indicating not at all important/difficult/confident) to 10 (indicating the most important/difficult/confident). The study assessed attitudes towards HTPs by the questions “Do you agree that HTPs are not addictive?”; “Do you agree that HTPs are better than cigarettes in terms of being less hazardous to health?”; “Do you agree that HTPs contain less harmful substances than cigarettes?”; “Do you agree that HTPs can help with smoking cessation?”; and “Do you agree that HTPs can reduce cigarette smoking?”, with possible responses of “Strongly agree,” “Agree,” “Disagree,” “Strongly disagree,” and “Don't know.”
      Research assistants conducted telephone follow-ups at 1 week and 1, 3, and 6 months. The primary outcome was the self-reported 7-day point prevalence of cigarette abstinence (PPA) at the 6 month follow-up. The secondary outcomes included: 1) self-reported 7-day PPA at the 1-week and 1- and 3-month follow-ups; 2) cigarette consumption reduction compared with baseline levels, excluding those who had successfully quit; 3) cigarette quit attempts lasting for more than 24 h; and 4) the level of readiness to quit at 1-week and 1-, 3-, and 6-month follow-ups. The study staff determined the frequency of HTP use within the previous 7 days and 30 days at each follow-up. The study measured the 7-day PPA using the questions: “Did you smoke any cigarettes in the past 7 days?” and “How long have you abstained from cigarettes?” The research team calculated the reduction in cigarette smoking by the change in the average number of cigarettes per day (CPD) compared to that at baseline. The study measured CPD using the questions: “How many cigarettes per day, on average, have you smoked in the past 7 days?” and “How many daily cigarettes, on average, have you smoked on weekdays and weekends, respectively, in the past 30 days?” (
      • Blank M.D.
      • Breland A.B.
      • Enlow P.T.
      • Duncan C.
      • Metzger A.
      • Cobb C.O.
      Measurement of smoking behavior: Comparison of self-reports, returned cigarette butts, and toxicant levels.
      ). We determined the number of cigarette quit attempts using the question, “Since our last talk, have you ever intentionally attempted to stop smoking cigarettes for more than 24 hours?” The study assessed the level of readiness to quit using the stages of the transtheoretical model. This tool comprises six statements, including “I have not decided to quit smoking” (pre-contemplation), “I will quit smoking after 6 months” (pre-contemplation), “I will quit smoking within 6 months” (contemplation), “I will quit smoking within 1 month” and “I will quit smoking within 1 week” (preparation), and “I don't smoke now” (action) (
      • Prochaska J.O.
      • Redding C.A.
      • Evers K.E.
      The transtheoretical model and stages of change.
      ). All measures discussed here are commonly used for the measurement of smoking behavior.

      2.5 Data analysis

      We performed the data analyses with the R programming language for statistical computing and graphics (version 4.0). We adopted a two-sided statistical significance level of 0.05 for all analyses.
      The study used descriptive statistics to detail participants' demographic characteristics and smoking profiles. We used frequency and percentage or mean and standard deviation (SD) to present categorical data and continuous data, respectively. We compared differences in baseline characteristics between the non-HTP users and HTP users using a chi-squared test for categorical variables and a one-way analysis of variance for continuous variables.
      By combining the data describing HTP use at baseline and at all follow-ups, we created a composite variable of different patterns of HTP use. We categorized the participants into HTP never-users (those who did not use HTPs at baseline nor at any follow-ups); baseline HTP users (those who used HTPs at baseline only); initiative HTP users (those who did not use HTPs at baseline but did at the 1-week, 1-month, or 3-month follow-ups); and persistent HTP users (those who used HTPs at baseline and at 1-week, 1-month, and 3-month follow-ups). We merged those who used HTPs at baseline or at the 1-week, 1-month, or 3-month follow-ups into any HTP users. We identified the participants who had self-reported 7-day PPA but subsequently reported cigarette use at any follow-ups as relapsed.
      Before performing the regression analyses, we used multiple imputations to handle missing values. We generated 30 datasets with the imputed missing data using the Markov chain Monte Carlo method (

      S. Van Buuren K. Groothuis-Oudshoorn G. Vink R. Schouten R. Robitzsch P. Rockenschaub L. Doove S. Jolani M. Moreno-Betancur I. White P. Gaffert F. Meinfelder B. Gray V. Arel-Bundock (2021, January 27). mice: Multivariate imputation by chained equations in R. https://cran.r-project.org/web/packages/mice/index.html.

      ;
      • White I.R.
      • Royston P.
      • Wood A.M.
      Multiple imputation using chained equations: Issues and guidance for practice.
      ). Then we fit regression parameters and corresponding standard errors (SEs) using all the imputed datasets and Rubin's rules (
      • White I.R.
      • Royston P.
      • Wood A.M.
      Multiple imputation using chained equations: Issues and guidance for practice.
      ).
      The study team performed univariable regression analyses with robust variance to obtain crude relative risks (RRs) for the association of HTP use with cigarette cessation outcomes at each follow-up, and then the multivariable regression analyses with robust variance to obtain adjusted RRs, after adjusting for baseline characteristics that significantly differed between the two groups. We performed linear regression analyses with the same steps as above to obtain the coefficients of correlation between HTP use and the percentage of reduction in cigarette smoking among the participants. We also performed the corresponding regression analyses to explore specific associations of different patterns of HTP use with cigarette cessation outcomes at the 6-month follow-up. Finally, we performed sensitivity analyses using the complete dataset.

      3. Results

      Of the 579 participants, we identified 106 (18.3%) HTP users, and 473 (81.7%) non-HTP users at baseline. Of the total participants, the study recruited 166 (28.7%), 34 (5.9), and 379 (65.5) via incoming calls, active referrals from other institutions, and outreach activities in schools or the community, respectively. The study found no significant differences in recruitment source (p = 0.07) and retention rate (74.5% vs. 74.2%, p = 0.95) between the HTP users and non-HTP users.
      Table 1 shows the participants' baseline characteristics. Their mean age was 19.2 (SD = 2.9) years, with HTP users being older than non-HTP users (19.9 [SD = 2.8] years vs. 19.0 [SD = 2.9] years; p = 0.004). Most of the participants were male (82.2%), in postsecondary education (67.5%), and single (97.9%). Approximately 38% of the participants were full-time students but also worked as part-time employees. The proportion of full-time students working part time was significantly higher among HTP users than among non-HTP users (52.9% vs. 35.0%; p = 0.001). The mean daily cigarette consumption was 9.3 (SD = 7.6), with HTP users consuming slightly fewer cigarettes daily than non-HTP users (8.1 [SD = 6.5] vs. 9.6 [SD = 7.8]; p = 0.06). The participants' mean age at smoking initiation was 14.6 (SD = 3.0) years. Among the HTP users, 11.3% (35/106) were daily HTP users. The participants had smoked for 4.9 (SD = 3.5) years on average. Approximately 74% (427/579) of the participants had attempted to quit cigarettes for more than 24 h in the past 12 months. More HTP users reported attempts to quit than non-HTP users (81.1% vs. 72.1%; p = 0.06), but the study identified no statistical significant difference. Compared to non-HTP users, significantly more HTP users had a mild level of nicotine dependence (76.7% vs. 66.3%; p = 0.04) and were prepared to quit smoking within 1 month (48.1% vs. 37.0%; p = 0.03). HTP users were significantly more confident in their ability to quit smoking than non-HTP users (6.7 ± 2.4 vs. 6.0 ± 2.6; p = 0.02). When comparing attitudes towards HTPs, significantly more HTP users than non-users agreed that “HTPs are better than cigarettes in terms of being less hazardous to health” (55.4% vs. 31.4%; p < 0.001); “HTPs contain less harmful substances than cigarettes” (51.1% vs. 23.1%; p < 0.001); and “HTPs can help with smoking cessation” (41.9% vs. 26.6%; p = 0.005). In addition, more HTP users agreed that “HTPs are not addictive” (25.0% vs. 18.5%; p = 0.18) and “HTPs can reduce cigarette smoking” (46.7% vs. 36.2%; p = 0.07) than non-HTP users, but this difference was not statistically significant. Among the HTP users, 90.3% (84/93) had used cigarettes before initiating HTP use, 4.3% (4/93) had used HTPs before initiating cigarette use, and 5.4% (5/93) could not remember the order in which they had started. The top three reasons reported by the HTP users for initiating HTP use were curiosity (48.5%), peer influence (39.4%), and use as a smoking cessation aid (15.2%).
      Table 1Characteristics of the youth smoking participants by the use of heated tobacco products at baseline.
      All participants

      (N = 579)
      Non-HTP users

      (n = 473)
      HTP users

      (n = 106)
      P value
      Sources0.07
       Incoming calls166(28.7)143(30.2)23(21.7)
       Referral cases34(5.9)24(5.1)10(9.4)
       Outreach recruitment379(65.5)306(64.7)73(68.9)
      Age19.2(2.9)19.0(2.9)19.9(2.8)0.004
      Sex0.28
       Male476(82.2)385(81.4)91(85.8)
       Female103(17.8)88(18.6)15(14.2)
      Educational attainment
      Missing values were excluded.
      0.16
       Lower secondary67(12.4)60(13.6)7(7.0)
       Upper secondary109(20.1)90(20.4)19(19.0)
       Post-secondary365(67.5)291(66.0)74(74.0)
      Employment status
      Missing values were excluded.
      0.001
       Full-time students176(31.7)158(35.0)18(17.3)
       Full-time students and part-time employed213(38.4)158(35.0)55(52.9)
       Fill-time employed146(26.3)119(26.4)27(26.0)
       Unemployed20(3.6)16(3.5)4(3.8)
      Marital Status
      Missing values were excluded.
      0.41
       Single522(97.9)424(97.7)98(99.0)
       Married/cohabitated11(2.1)10(2.3)1(1.0)
      Age of starting smoking
      Missing values were excluded.
      14.6(3.0)14.5(2.8)14.9(3.9)0.23
      Year of regular smoking
      Missing values were excluded.
      4.9(3.5)4.9(3.4)5.7(4.6)0.25
      Daily cigarette consumption9.3(7.6)9.6(7.8)8.1(6.5)0.06
      Dosage of HTP consumption
       Less than 1 time per week59(55.7)
       1–6 times per week35(33.0)
       Daily user12(11.3)
      Quit attempt >24 h within the past year.0.06
       Yes427(73.7)341(72.1)86(81.1)
       No152(26.3)132(27.9)20(18.9)
      Nicotine dependency by the Fagerstrom Test0.04
       Mild (0–3)388(68.2)309(66.3)79(76.7)
       Moderate (4–5)132(23.2)111(23.8)21(20.4)
       Severe (6–10)49(8.6)46(9.9)3(2.9)
      Prepare to quit within 1 month0.03
       Yes226(39.0)175(37.0)51(48.1)
       No353(61.0)298(63.0)55(51.9)
      Perspectives on importance of quitting smoking (1−10), mean (SD)
      Missing values were excluded.
      6.9(2.4)6.9(2.3)6.8(2.6)0.63
      Perspectives on confidence of quitting smoking (1–10), mean (SD)
      Missing values were excluded.
      6.2(2.6)6.0(2.6)6.7(2.4)0.02
      Perspectives on difficulty of quitting smoking (1–10), mean (SD)
      Missing values were excluded.
      5.6(2.9)6.0(2.8)6.0(2.8)0.39
      Attitudes towards the HTPs
      Missing values were excluded.
       HTPs aren't addictive0.18
      Strongly agree/agree83(20.0)60(18.5)23(25.0)
      Strongly disagree/disagree/don't know333(80.0)264(81.5)69(75.0)
       HTPs are better than cigarettes in terms of less health hazardous<0.001
      Strongly agree/agree152(36.5)102(31.4)51(55.4)
      Strongly disagree/disagree/don't know264(63.4)223(68.6)41(44.6)
       HTPs contain less harmful substances<0.001
      Strongly agree/agree122(29.3)75(23.1)47(51.1)
      Strongly disagree/disagree/don't know295(70.7)250(76.9)45(48.9)
       HTPs can help with smoking cessation0.005
      Strongly agree/agree125(30.0)86(26.6)39(41.9)
      Strongly disagree/disagree/don't know291(70.0)237(73.4)54(58.1)
       HTPs can reduce smoking of cigarettes0.07
      Strongly agree/agree160(38.6)117(36.2)43(46.7)
      Strongly disagree/disagree/don't know255(61.4)206(63.8)49(53.3)
      Note: Data are n (%) or mean (SD).
      a Missing values were excluded.
      Of the 473 non-HTP users at baseline, 22 reported the use of HTPs at the 1-week; 1-, 3-, or 6-month follow-ups. As Table 2 shows, those who were full-time students and part-time employed, and those who agreed that HTPs were not addictive were more likely to use HTPs after joining the smoking cessation service.
      Table 2Baseline predictors of HTP imitation during the follow-up period in non-HTP users at baseline.
      HTP Initiation (%)
      A total of 22 non-HTP users at baseline reported the HTPs initiation at 1w/1 m/3 m/6 m follow-ups.
      Crude RRs (95% CI)
      Multiply imputed.
      HTP imitative users refer to the non-HTP users at baseline and any follow-ups.
      P valueAdjusted RRs (95% CI)
      Multiply imputed.
      HTP imitative users refer to the non-HTP users at baseline and any follow-ups.
      Multivariable logistic regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      P value
      Sources
       Incoming calls6.3%11
       Referral cases/Outreach recruitment3.9%0.92(0.73, 1.16)0.480.91(0.68, 1.22)0.54
      Age4.7%1.09(0.96, 1.27)0.261.03(0.97, 1.08)0.35
      Sex
       Male4.4%11
       Female3.4%0.97(0.62, 1.53)0.900.73(0.41, 1.30)0.73
      Educational attainment
      A total of 22 non-HTP users at baseline reported the HTPs initiation at 1w/1 m/3 m/6 m follow-ups.
       Lower secondary5.0%11
       Upper secondary2.2%0.43(0.07, 2.67)0.370.64(0.13, 3.28)0.60
       Post-secondary5.2%1.03(0.29, 3.68)0.961.55(0.40, 6.03)0.53
      Employment status
      A total of 22 non-HTP users at baseline reported the HTPs initiation at 1w/1 m/3 m/6 m follow-ups.
       Full-time students5.1%11
       Full-time students and part-time employed7.6%2.27(0.84, 6.13)0.113.56(1.16, 7.99)0.03
       Full-time employed0%0.86(0.38, 1.96)0.730.94(0.34, 2.65)0.91
       Unemployed2.5%0.83(0.17, 3.98)0.820.58(0.11, 2.99)0.52
      Marital status
      A total of 22 non-HTP users at baseline reported the HTPs initiation at 1w/1 m/3 m/6 m follow-ups.
       Single4.5%11
       Married/cohabitated10.0%0.94(0.59, 1.50)0.780.89(0.54, 1.45)0.53
      Age of starting smoking4.7%0.95(0.82, 1.10)0.490.90 (0.78, 1.04)0.16
      Year of regular smoking
      A total of 22 non-HTP users at baseline reported the HTPs initiation at 1w/1 m/3 m/6 m follow-ups.
      4.7%1.12 (0.97, 1.29)0.141.10(0.96, 1.27)0.17
      Daily cigarette consumption4.7%0.98(0.92, 1.04)0.490.93(0.87, 0.998)0.04
      Nicotine dependency
       Mild (0–3)3.9%11
       Moderate (4–5)5.4%1.53(0.60, 3.95)0.381.42(0.53, 3.79)0.48
       Severe (6–10)4.3%1.04(0.23, 4.74)0.972.52(0.61, 9.41)0.20
      Prepare to quit within 1 month
       No4.7%11
       Yes3.9%0.63(0.24, 1.63)0.340.83(0.36, 1.88)0.83
      Quit attempt >24 h within the past year.
       No6.2%11
       Yes3.5%0.54(0.23, 1.30)0.170.95(0.41, 2.21)0.90
      Perspectives on importance of quitting smoking
      A total of 22 non-HTP users at baseline reported the HTPs initiation at 1w/1 m/3 m/6 m follow-ups.
      4.7%0.85(0.71, 1.01)0.060.86(0.72, 1.03)0.10
      Perspectives on confidence of quitting smoking
      A total of 22 non-HTP users at baseline reported the HTPs initiation at 1w/1 m/3 m/6 m follow-ups.
      4.7%0.89(0.76, 1.04)0.150.87(0.73, 1.04)0.12
      Perspectives on difficulty of quitting smoking
      A total of 22 non-HTP users at baseline reported the HTPs initiation at 1w/1 m/3 m/6 m follow-ups.
      4.7%1.01(0.86, 1.17)0.950.96(0.81, 1.12)0.57
      Attitudes towards the HTPs
      A total of 22 non-HTP users at baseline reported the HTPs initiation at 1w/1 m/3 m/6 m follow-ups.
       HTPs aren't addictive
      Strongly agree/agree10.0%3.53(1.70, 7.38)0.0012.86(1.24, 6.61)0.01
      Strongly disagree/disagree/don't know2.3%11
       HTPs are better than cigarettes in terms of less health hazardous
      Strongly agree/agree4.7%1.31(0.03, 57.98)0.892.03(0.82, 5.05)0.13
      Strongly disagree/disagree/don't know3.0%11
       HTPs contain less harmful substances
      Strongly agree/agree4.8%3.06(1.46, 6.42)0.0032.22(0.90, 5.47)0.08
      Strongly disagree/disagree/don't know3.0%11
       HTPs can help with smoking cessation
      Strongly agree/agree2.9%1.35(0.93, 1.98)0.110.50(0.21, 1.19)0.12
      Strongly disagree/disagree/don't know2.9%1
       HTPs can reduce smoking of cigarettes
      Strongly agree/agree2.3%1.19(0.82, 1.74)0.360.74(0.28, 1.94)0.54
      Strongly disagree/disagree/don't know3.1%
      a A total of 22 non-HTP users at baseline reported the HTPs initiation at 1w/1 m/3 m/6 m follow-ups.
      b Multiply imputed.
      c HTP imitative users refer to the non-HTP users at baseline and any follow-ups.
      d Multivariable logistic regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      Table 3 presents the association between HTP use at baseline and cigarette cessation outcomes. Self-reported 7-day PPA was statistically lower among HTP users than among non-HTP users at both the 3- and 6-month follow-ups (3-month: 15.7% vs. 26.2%, p = 0.04; 6-month: 19.0% vs. 34.2%, p = 0.009), with adjusted RRs of 0.50 (95% confidence interval [CI]: 0.29–0.86; p = 0.01) at 3 months and 0.47 (95% CI: 0.24–0.91; p = 0.03) at 6 months. The study found no statistically significant difference in self-reported 7-day PPA at the 1-week and 1-month follow-ups between the HTP users and non-HTP users. The study did not observe any statistically significant differences between the HTP users and non-HTP users in the mean percentage of reduction in cigarette smoking (excluding the quitters), the number of cigarette quit attempts, and the level of readiness to quit at any follow-ups. The number of youth smokers who had self-reported 7-day PPA but relapsed at any subsequent follow-up through the study period was significantly higher among the HTP users than among the non-HTP users (60.7% vs. 33.9%; p = 0.008), with an adjusted RR of 4.56 (95% CI: 1.17–17.79; p = 0.03).
      Table 3Associations of HTP use at baseline and cigarette cessation outcomes.
      n/N (%)Crude RRs (95% CI)
      Multiply imputed.
      HTP users refer to the non-HTP users at baseline.
      P valueAdjusted RRs (95% CI)
      Multiply imputed.
      HTP users refer to the non-HTP users at baseline.
      Multivariable logistic regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      P value
      Non-HTP usersHTP user
      Self-reported 7-day point prevalence of cigarette abstinence
      1 week56/380(14.7)16/83(19.3)1.24(1.01, 1.51)0.041.01(0.79, 1.28)0.96
      1 month84/418(20.1)18/92(19.6)0.96(0.79, 1.18)0.720.84(0.66, 1.07)0.16
      3 month106/404(26.2)14/89(15.7)0.81(0.66, 0.99)0.040.50(0.29, 0.86)0.01
      6 month120/351(34.2)15/79(19.0)0.50(0.29, 0.84)0.0090.47(0.24, 0.91)0.03
      Attempted to quit cigarettes ≥ 24 h
      1 week178/376(47.3)45/83(54.2)1.24(0.77, 1.67)0.381.14(0.92, 1.41)0.23
      1 month212/383(55.4)39/80(48.8)0.76(0.48, 1.24)0.290.69(0.41, 1.15)0.16
      3 month148/332(44.6)29/74(39.2)0.86(0.53, 1.40)0.550.72(0.43, 1.20)0.21
      6 month223/341(65.4)51/77(66.2)1.02(0.62, 1.68)0.930.81(0.48, 1.37)0.43
      Prepared to quit within 30 days
      1 week125/355(35.2)25/79(31.6)0.91(0.54, 1.51)0.710.74(−0.43, 1.27)0.27
      1 month85/310(27.4)15/63(23.8)0.91(0.56, 1.50)0.720.60(0.35, 1.01)0.06
      3 month126/280(45.0)36/69(52.2)1.20(0.72, 1.98)0.491.18(0.70, 1.98)0.53
      6 month96/237(40.5)23/63(36.5)0.84(0.48, 1.45)0.521.11(0.67, 1.87)0.68
      Relapse cigarette consumption during the follow-ups
      Participants who had self-reported 7-day point prevalence of cigarette abstinence, but relapsed at any subsequent follow-up.
      Relapsed62/183(33.9)17/28(60.7)3.02(1.33, 6.83)0.0084.56(1.17, 17.79)0.03
      Mean of %(SD)Crude coefficient (95% CI)
      Multiply imputed.
      HTP users refer to the non-HTP users at baseline.
      P valueAdjusted coefficient (95% CI)
      Multiply imputed.
      HTP users refer to the non-HTP users at baseline.
      Multivariable linear regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      P value
      Reduction of cigarette consumption compared to baseline
      Excluded quitters in both nominator and denominator.
      1 week31.8%(0.30)36.0%(0.34)0.04(−0.04, 0.12)0.120.02(−0.15, 0.10)0.71
      1 month33.9%(0.29)28.7%(0.27)−0.05(−0.13, 0.03)0.27−0.05(−0.17, 0.06)0.37
      3 month31.3%(0.31)28.4%(0.34)−0.03(−0.05, 0.11)0.31−0.07(−0.19, 0.06)0.29
      6 month31.5%(31.5)24.5%(0.30)−0.07(−0.16, 0.02)0.09−0.13(−0.26, 0.003)0.06
      Note: RR, Relative Risk; CI, Confidence Interval; SD, Standard deviation.
      a Multiply imputed.
      b HTP users refer to the non-HTP users at baseline.
      c Multivariable logistic regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      d Multivariable linear regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      e Participants who had self-reported 7-day point prevalence of cigarette abstinence, but relapsed at any subsequent follow-up.
      f Excluded quitters in both nominator and denominator.
      Table 4Associations of different HTP use patterns and cigarette cessation outcomes at 6 months.
      Different HTP use patternsAdjusted RR (95% CI)
      Multiply imputed.
      HTP users refer to the non-HTP users at baseline.
      Multivariable logistic regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      P value
      Self-reported 7-day point prevalence of cigarette abstinence
       Never-HTP users (n = 453)1
       Baseline HTP users (n = 17)0.38(0.21, 0.69)0.03
       Initiative HTPs users (n = 20)0.45(0.15, 0.92)0.02
       Persistent HTP users (n = 89)0.18(0.04, 0.86)0.001
      Attempted to quit cigarettes ≥24 h
       Never-HTP users (n = 453)1
       Baseline HTP users (n = 17)0.76(0.44, 1.31)0.65
       Initiative HTPs users (n = 20)1.16(0.40, 3.37)0.79
       Persistent HTP users (n = 89)1.31(0.40, 4.30)0.32
      Prepared to quit within 30 days
       Never-HTP users (n = 453)1
       Baseline HTP users (n = 17)1.21(0.70, 2.08)0.90
       Initiative HTPs users (n = 20)2.17(0.84, 5.61)0.11
       Persistent HTP users (n = 89)1.08(0.33, 3.55)0.50
      Reduction of cigarette consumption compared to baseline
      Excluded quitters in both nominator and denominator.
      Adjusted coefficient (95% CI)
      Multiply imputed.
      HTP users refer to the non-HTP users at baseline.
      Multivariable linear regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      P value
      Baseline HTP users (n = 17)−0.11(−0.26, 0.03)0.13
      Initiative HTPs users (n = 20)−0.03(−0.15, 0.21)0.76
      Persistent HTP users (n = 89)−0.07(−0.15, 0.009)0.08
      Any use of HTPs at baseline and follow-upsAdjusted RR (95% CI)
      Multiply imputed.
      HTP users refer to the non-HTP users at baseline.
      Multivariable logistic regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      P value
      Self-reported 7-day point prevalence of cigarette abstinence
       Never-HTP users (n = 453)1
       Any HTP users (n = 126)0.40(0.25, 0.86)0.01
      Attempted to quit cigarettes ≥24 h
       Never-HTP users (n = 453)1
       Any HTP users (n = 126)0.84(0.52, 1.38)0.50
      Prepared to quit within 30 days
       Never-HTP users (n = 453)1
       Any HTP users (n = 126)1.42(0.87, 2.30)0.16
      Reduction of cigarette consumption compared to baseline
      Excluded quitters in both nominator and denominator.
      Adjusted coefficient (95% CI)
      Multiply imputed.
      HTP users refer to the non-HTP users at baseline.
      Multivariable linear regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      P value
      Any users (n = 126)−0.11(−0.24, 0.01)0.08
      Note: RR, Relative Risk; CI, Confidence Interval; SD, Standard deviation; Never-HTP users, those who did not use HTP at baseline and any follow-ups; Baseline HTP user, those who used HTP at baseline only; Initiative HTPs users, those who did not use HTPs at baseline but at 1w/1 m/3 m follow up; Persistent HTP users, those who used HTPs at baseline and 1w/1 m/3 m follow-up; Any users, those who used HTPs at baseline or 1w/1 m/3 m follow-up.
      a Multiply imputed.
      b HTP users refer to the non-HTP users at baseline.
      c Multivariable logistic regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      d Multivariable linear regression with robust variance, adjusting for age, education attainment, employment status, age of starting smoking, year of regular smoking, daily cigarette consumptions, level of nicotine dependency, readiness to quit, quit attempt, perceived importance and confidence of quitting smoking, attitudes towards the HTPs, and the sources of the participants.
      e Excluded quitters in both nominator and denominator.
      Table 4 shows that compared with the HTP never-users (n = 453), the baseline HTP users (n = 17), initiative HTP users (n = 20), and persistent HTP users (n = 89) were significantly less likely to abstain from cigarettes. HTP use patterns were not associated with the mean percentage of reduction in cigarette smoking, the number of cigarette quit attempts, or the level of readiness to quit at 6 months. The study observed similar results for cigarette cessation outcomes at the 6-month follow-up for any HTP users (n = 126) and HTP never-users. Sensitivity analyses using the sample of complete cases (Appendix online in Supplementary Table) demonstrated results similar to those reported here.

      4. Discussion

      To the best of our knowledge, this study is the first to explore the prospective predictors of HTP initiation and the association of HTP use with cigarette cessation outcomes among youth smokers who were willing to receive telephone counseling to support smoking cessation. The findings indicated that use of HTPs was negatively associated with abstinence from cigarettes over a 6-month period among youth smokers using telephone cessation services in Hong Kong. This study, therefore, reveals that HTPs are likely ineffective tools to aid smoking cessation in this population.
      Employment status and the belief that HTPs were not addictive were strong predictors of future HTP use among youth smokers. Comparison of baseline characteristics showed that youth HTP users were less dependent on nicotine, more ready to quit within 1 month, more had previously attempted to quit, and had more confidence in their ability to quit smoking. These findings mirror the use patterns that have been previously reported in Korea, Japan, and the United States (
      • Sutanto E.
      • Miller C.
      • Smith D.M.
      • O'Connor R.J.
      • Quah A.
      • Cummings K.M.
      • Xu S.
      • Fong G.T.
      • Hyland A.
      • Ouimet J.
      • Yoshimi I.
      • Mochizuki Y.
      • Tabuchi T.
      • Goniewicz M.L.
      Prevalence, use behaviors, and preferences among users of heated tobacco products: findings from the 2018 ITC Japan survey.
      ;
      • Kang S.Y.
      • Lee S.
      • Cho H.J.
      Prevalence and predictors of heated tobacco product use and its relationship with attempts to quit cigarette smoking among Korean adolescents.
      ;
      • Dunbar M.S.
      • Seelam R.
      • Tucker J.S.
      • Rodriguez A.
      • Shih R.A.
      • D'Amico E.J.
      Correlates of awareness and use of heated tobacco products in a sample of US young adults in 2018–2019.
      ). Despite the aforementioned variables being common predictors of abstinence from conventional cigarettes, the youth HTP users reported a lower quit rate. HTP users and non-HTP users reported similar levels of readiness to quit and a similar number of cigarette quit attempts at each follow-up. The study did not identify any difference in cigarette smoking reduction between the two groups, after excluding quitters. Additionally, HTP users were significantly more likely to relapse during the study period. These discrepancies in the association between common predictors and outcomes reveal that smoking cessation was significantly more difficult among youth HTP users than among non-HTP users.
      The negative association between HTP use and cigarette abstinence may be linked to the patterns of HTP use and reasons for initiating HTP use. According to previous qualitative interview data, youth smokers are more likely to experiment with a multitude of tobacco products that have features of perceived luxury, prestige, or novelty, such as HTPs (
      • McKelvey K.
      • Popova L.
      • Kim M.
      • Chaffee B.W.
      • Vijayaraghavan M.
      • Ling P.
      • Halpern-Felsher B.
      Heated tobacco products likely appeal to adolescents and young adults.
      ). We found that most of the HTP users had initiated HTP use due to curiosity or peer influence, rather than as smoking cessation aids. Therefore, youth cigarette smokers may be less likely than older smokers to consider switching from cigarettes to HTPs, which may hinder users' decisions to completely abstain from cigarettes (
      • Lee C.M.
      • Kim C.Y.
      • Lee K.
      • Kim S.
      Are heated tobacco product users less likely to quit than cigarette Smokers? Findings from THINK (Tobacco and health IN Korea) study.
      ;
      • Mallock N.
      • Pieper E.
      • Hutzler C.
      • Henkler-Stephani F.
      • Luch A.
      Heated tobacco products: A review of current knowledge and initial assessments.
      ;
      • Tucker J.S.
      • Shadel W.G.
      • Golinelli D.
      • Seelam R.
      • Siconolfi D.
      Motivation to quit cigarettes and alternative tobacco products: Prevalence and correlates among youth experiencing homelessness.
      ). Furthermore, as reported in a previous study, youth smokers used HTPs not as substitutes for cigarettes but as an alternative in situations where conventional cigarette smoking was not allowed, such as smoke-free areas or schools (
      • Ratajczak A.
      • Jankowski P.
      • Strus P.
      • Feleszko W.
      Heat not burn tobacco product-a new global trend: Impact of heat-not-burn tobacco products on public health, a systematic review.
      ). However, as with the use of traditional nicotine replacement therapies, HTP use may not promote nicotine abstinence (
      • Hwang J.H.
      • Ryu D.H.
      • Park S.W.
      Heated tobacco products: Cigarette complements, not substitutes.
      ). Rather, the use of HTPs and cigarettes may increase nicotine intake. Previous studies have shown that higher nicotine dependence is a barrier to quitting smoking and a predictor of relapse among youth smokers (
      • El Mhamdi S.
      • Sriha A.
      • Bouanene I.
      • Ben Salah A.
      • Ben Salem K.
      • Soltani M.S.
      Predictors of smoking relapse in a cohort of adolescents and young adults in Monastir (Tunisia).
      ;
      • Siqueira L.M.
      • Rolnitzky L.M.
      • Rickert V.I.
      Smoking cessation in adolescents: The role of nicotine dependence, stress, and coping methods.
      ). In line with these findings, while both HTP users and non-HTP users received assistance from the cessation service, HTP users achieved a lower cigarette abstinence rate than their non-HTP-using comparators. Given that HTP does not aid cessation, policy-makers should consider policies or strategies to deter HTP use among youth smokers under 25 years of age in Hong Kong (
      • Chung S.J.
      • Kim B.K.
      • Oh J.H.
      • Shim J.S.
      • Chang Y.S.
      • Cho S.H.
      • Yang M.S.
      Novel tobacco products including electronic cigarette and heated tobacco products increase risk of allergic rhinitis and asthma in adolescents: Analysis of Korean youth survey.
      ;
      • Leigh N.J.
      • Tran P.L.
      • O’Connor R.J.
      • Goniewicz M.L.
      Cytotoxic effects of heated tobacco products (HTP) on human bronchial epithelial cells.
      ).
      We examined sociodemographic and smoking-related predictors of HTP initiation in youth non-HTP users. In contrast to the findings of a previous study, which reported that younger age and higher educational attainment were predictors of HTP use among adult smokers in Hong Kong (
      • Luk T.T.
      • Weng X.
      • Wu Y.S.
      • Chan H.L.
      • Lau C.Y.
      • Kwong A.C.
      • Lai V.W.
      • Lam T.H.
      • Wang M.P.
      Association of heated tobacco product use with smoking cessation in Chinese cigarette smokers in Hong Kong: a prospective study.
      ), we found that youth non-HTP users who agreed that HTPs were not addictive and who were full-time students with part-time employment were more likely to initiate HTP use. Studies have demonstrated that positive attitudes towards HTPs are linked to HTP initiation among youth in many countries (
      • Dunbar M.S.
      • Seelam R.
      • Tucker J.S.
      • Rodriguez A.
      • Shih R.A.
      • D'Amico E.J.
      Correlates of awareness and use of heated tobacco products in a sample of US young adults in 2018–2019.
      ;
      • Sutanto E.
      • Miller C.
      • Smith D.M.
      • O'Connor R.J.
      • Quah A.
      • Cummings K.M.
      • Xu S.
      • Fong G.T.
      • Hyland A.
      • Ouimet J.
      • Yoshimi I.
      • Mochizuki Y.
      • Tabuchi T.
      • Goniewicz M.L.
      Prevalence, use behaviors, and preferences among users of heated tobacco products: findings from the 2018 ITC Japan survey.
      ). A 10-year cohort study found that adolescents aged 14–18 years who spent more hours working for pay had an elevated risk of initiating HTP use relative to adolescents who did not take up employment (
      • Ramchand R.
      • Ialongo N.S.
      • Chilcoat H.D.
      The effect of working for pay on adolescent tobacco use.
      ). Our findings add important information to the literature by demonstrating a similar association between employment and initiation of HTP use.
      This study has some limitations, however. First, given the observational design of the cohort study, we could not draw a causal inference, as the participants self-selected to use HTPs. Although we adjusted for sociodemographic factors that predicted HTP use and known predictors of cigarette cessation, including employment status and agreement that HTPs were not addictive, the potential effects of unmeasured and residual confounders could not be excluded. Second, the study team conducted this cohort study through a telephone-based smoking cessation service. Even though this study also actively recruited participants from the community, this study could not access youth who were not willing to use such services and were unreachable via this telephone-based service. Additionally, due to the difficulties in defining exclusive cigarette users and accounting for the effects of other tobacco products, this study excluded individuals who were using other tobacco-based products. These inclusion and exclusion criteria led to a biased sample, as dual users tend to use other tobacco products. Most smokers (82.2%) in the cohort were male, which is in-line with the expected ratio of tobacco users by sex in the Hong Kong population (male: 85.7% vs. female: 14.3%) (

      Census and Statistics Department. (2019, June 8). Thematic household survey report no. 70: Pattern of smoking. https://www.statistics.gov.hk/pub/B11302702020XXXXB0100.pdf.

      ). Nonetheless, this imbalance may decrease the generalizability of our findings. Further studies including more female youth smokers could be conducted at general cessation clinics to explore the association of HTP use with cigarette cessation outcomes among a sex-balanced youth population. Third, all measures were self-reported and the research team determined that only the 7-day PPA inferred abstinence. Although the original service performed a biochemical validation of abstinence, the study carried out validation only for participants who reported abstinence from all nicotine-containing products (including HTPs). Evidence surrounding the ability of existing biochemical methods, including exhaled carbon monoxide and cotinine tests, to distinguish cigarette smoking from HTP use remains scarce (
      • Benowitz N.L.
      • Bernert J.T.
      • Foulds J.
      • Hecht S.S.
      • Jacob P.
      • Jarvis M.J.
      • Joseph A.
      • Oncken C.
      • Piper M.E.
      Biochemical verification of tobacco use and abstinence: 2019 update.
      ). Smokers who completely switch to HTPs are still exposed to carbon monoxide (albeit at a lower level) and nicotine in HTP emissions (
      • Auer R.
      • Concha-Lozano N.
      • Jacot-Sadowski I.
      • Cornuz J.
      • Berthet A.
      Heat-not-burn tobacco cigarettes: Smoke by any other name.
      ). Nevertheless, self-reported abstinence is considered acceptable given the minimal contact between the participants and investigators (
      • Benowitz N.L.
      • Bernert J.T.
      • Foulds J.
      • Hecht S.S.
      • Jacob P.
      • Jarvis M.J.
      • Joseph A.
      • Oncken C.
      • Piper M.E.
      Biochemical verification of tobacco use and abstinence: 2019 update.
      ). Fourth, given that participants who did not want to quit are more likely to skip follow-ups, the missing data may have led to bias. Despite a satisfactory retention rate of 74.3%, with no difference between the HTP users and non-HTP users, the missing values account for 16.71% of the baseline and follow-up data. The study used multiple imputations to address this issue, which reduced bias and increased the precision of the estimates while preserving the uncertainties of the missing data. The similarity of the results obtained from the primary analyses and complete case analyses (Appendix online in Supplementary Table) suggests that our use of multiple imputations was reliable. Finally, this study did not assess the reasons for youths' initiating HTP use during the follow-up period. As reported by the HTP users at baseline, the main reasons for HTP initiation among the youth were curiosity and peer influence, which are different from reasons that adult HTP users report. Studies should obtain qualitative information from youth HTP users to explore their reasons for HTP initiation and their experiences using HTPs. Such information may enhance our understanding of the association between HTP use and cigarette cessation among youth smokers.

      5. Conclusion

      This study showed that among youth smokers who intended to quit smoking with the assistance of a telephone-based cessation service in Hong Kong, HTP users were less likely to abstain from tobacco use than non-HTP users. These findings reveal that HTPs are ineffective tools to aid smoking cessation in this population.
      The following is the supplementary data related to this article.

      Ethics approval and consent to participate

      Ethical approval was obtained from the Institutional Review Board (UW 05-185 T/848). This study was registered on ClinicaslTrials.gov (NCT02758028). Considering the wishes of youth smokers to keep their smoking status confidential from their parents and join the service anonymously, oral consent to partake in the project was obtained before providing phone counseling, and written consent from parents was not required, which was discussed and approved by the ethics committee. The participants reserved the right to terminate the telephone counseling service at any time throughout the service without any consequences. Participants' confidentiality was ensured, and their verbal consent and counseling content were audio-recorded.

      Availability of data and materials

      The data that support the findings of this study are available from the Tobacco and Alcohol Control Office, the Department of Health in Hong Kong, but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. Data are however available from the authors upon reasonable request and with permission of the Tobacco and Alcohol Control Office, the Department of Health in Hong Kong.

      CRediT authorship contribution statement

      Wei Xia: Conceptualization, Methodology, Formal analysis, Investigation, Writing - Original Draft, Writing - Review & Editing. William Ho Cheung Li: Conceptualization, Resources, Writing - Original Draft, Supervision, Funding acquisition. Yuan Hui Luo: Investigation, Project administration, Writing - Review & Editing. Ting Na Liang: Investigation, Validation, Project administration, Writing - Review & Editing. Laurie Long Kwan Ho: Investigation, Validation, Writing - Review & Editing. Ankie Tan Cheung: Investigation, Project administration, Writing - Review & Editing. Peige Song: Formal analysis, Software, Data Curation, Resources, Writing - Review & Editing.

      Declaration of competing interest

      The authors declare that they have no competing interests.

      Acknowledgements

      We would like to thank the youth smokers for their participation in this project, and Ms. Vanessa Lai War Yeung and Ms. Annie On Ni Yip for their contribution to the Youth Quitline service. We also thank Audrey Holmes, MA, from the AsiaEdit Team for editing a draft of this manuscript.

      Funding

      This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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