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 randomized controlled trial. MEASUREMENTS: The sample was divided into groups of e-cigarette users: early users (at 13-14 years), late users (at 14-15 years) and never users (at 13-14 and 14-15 years). Dependent variables were self-reported regular e-cigarette and cigarette use and ever cigarette use at 15-16 years. Covariates were assessed. FINDINGS: Early and late users compared with never users were significantly more likely to be regular e-cigarette users [early: odds ratio (OR) = 9.42, 95% confidence interval (CI) = 5.38, 16.49, P < 0.001; late: OR = 6.89, 95% CI = 4.11, 11.54, P < 0.001], ever cigarette users (early: OR = 7.96, 95% CI = 6.02, 10.53, P < 0.001; late: OR = 5.13, 95% CI = 3.85, 6.84, P < 0.001) and regular cigarette users (early: OR = 7.80, 95% CI = 3.99, 15.27, P < 0.001; late: OR = 4.34, 95% CI = 1.93, 9.77, P < 0.001) 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 < 0.001), 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 = 0.498). Controlling for covariates did not change the findings. CONCLUSIONS: Adolescents in England who report using e-cigarettes at age 13-14 years have higher rates of subsequently initiating cigarette use than adolescents who report using e-cigarettes at age 14-15 years, a difference that may be attributable to a longer period of time to initiate cigarette use in former group.