Association between age at first reported e‐cigarette use and subsequent regular e‐cigarette, ever cigarette and regular cigarette use

Background and Aims: Association of electronic cigarette use and subsequent smoking has received considerable attention, although age of first use has not. This study tested differences in regular (e-cigarettes, cigarettes) and ever (cigarettes) use between e-cigarette user groups: early versus never users, late versus never users, early versus late users and effects of controlling for covariates.
Design: Prospective study with 12- and 24-month follow-up of e-cigarette/cigarette ever/regular use with data from an intervention.
Setting: Forty-five schools in England (Staffordshire and Yorkshire).
Participants: Never smokers (3289 13-14 year olds) who were part of a cluster randomised controlled trial.
Measurements: Sample divided into groups of e-cigarette users: early users (at 13-14 years), late users (at 14-15 years), never users (at 13-14 and 14-15 years). Dependent variables were self-reported regular e-cigarette and cigarette use, ever cigarette use at 15-16 years. Covariates were assessed.
Findings: Early users and late users compared with never users were significantly more likely to be regular e-cigarette users (early: OR=9.42, 95%CI=5.38, 16.49, p<.001; late: OR=6.89, 95%CI=4.11, 11.54, p<.001), ever cigarette users (early: OR=7.96, 95%CI=6.02, 10.53, p<.001; late: OR=5.13, 95%CI=3.85, 6.84, p<.001), and regular cigarette users (early: OR=7.80, 95%CI=3.99, 15.27, p<.001; late: OR=4.34, 95%CI=1.93, 9.77, p<.001) at age 15-16 years. Late users compared with early users had significantly lower rates of ever use of cigarettes at 15-16 years (OR=0.48, 95%CI=0.35, 0.66, p<.001), although this difference was non-significant at 12 months after first use of e-cigarettes (OR=0.89, 95%CI 0.64, 1.25, p = .498). Controlling for covariates did not change findings.
Conclusions: Adolescents in England who report using e-cigarettes at 13-14 years of age have higher rates of subsequently initiating cigarette use than adolescents who report using e-cigarettes at 14-15 years, a difference that may be attributable to a longer period of time to initiate cigarette use in former group.
Key words: electronic nicotine delivery systems; e-cigarettes; smoking; harm reduction; intervention.