Experimenting first with e‐cigarettes versus first with cigarettes and transition to daily cigarette use among adolescents: the crucial effect of age at first experiment.

Background and aims: Most studies in English‐speaking countries have found a positive association between e‐cigarette experimentation and subsequent daily tobacco smoking among adolescents. However, this result may not be valid in other cultural contexts; in addition, few studies have assessed whether this association varies with the subject' age at the time of e‐cigarette experimentation. This study aimed to estimate the association between experimenting first with e‐cigarette (rather than tobacco) and subsequent daily smoking according to age at the time of experimentation. Design Secondary analysis; risk ratios (RRs) computed using modified Poisson regressions with inverse probability weighting. Setting: A cross‐sectional nation‐wide representative survey performed in 2017 in France. Participants: French adolescents (n = 24 111), aged 17 to 18.5 years, who had previously experimented with either e‐cigarettes or tobacco. Measures Exposure was defined as the experimentation with e‐cigarettes first (whether or not followed by experimentation with tobacco); the outcome as daily tobacco smoking at the time of data collection. Gender, age, literacy, socio‐economic status, pre‐exposure repeat school years and experimentation with drunkeness, 3 licit and 8 illicit drugs were adjusted for. Uncertainties about the sequence of events defining exposure were handled by the definition of three patterns of exposure, to avoid a misclassification bias. Findings Exposure reduced the risk of transition to daily smoking: RR = 0.58, 95% confidence interval (CI) = 0.54, 0.62. This effect increased in a linear manner with age at exposure (RR = 0.87, 95% CI = 0.78; 0.98 for 1 year, P < 0.001): from RR = 1.30, 95% CI = 1.09; 1.54 at age 9 to RR = 0.38, 95% CI = 0.32; 0.45 at age 17. Conclusions: Experimenting with e‐cigarettes first (as opposed to tobacco first) appears to be associated with a reduction in the risk of daily tobacco smoking among French adolescents aged 17–18.5, but this risk varies negatively with age at experimentation, and early e‐cigarette experimenters are at higher risk. [ABSTRACT FROM AUTHOR]