Evidence that an intervention weakens the relationship between adolescent electronic cigarette use and tobacco smoking: A 24 month prospective study

Background: The electronic cigarette (e-cigarette) use to subsequent smoking relationship in adolescents has received much attention. Whether an intervention to reduce smoking initiation attenuated this relationship was assessed.
Method: Data were from 3994 adolescent never smokers (aged 13-14 years at baseline) as part of a cluster randomised controlled trial. Self-report measures of smoking, e-cigarette use and covariates were assessed and used to predict ever smoked cigarettes, any recent tobacco smoking, and regularly smoked cigarettes at 24-month follow-up.
Results: Baseline ever use of e-cigarettes was associated with ever smoked cigarettes (OR= 4·03, 95%CI 3·33—4·88; controlling for covariates, OR=2·78, 95%CI 2·20—3·51), any recent tobacco smoking (OR=3·38, 95%CI 2·72—4·21; controlling for covariates, OR=2·17, 95%CI 1·76—2·69) and regularly smoked cigarettes (OR=3·60, 95%CI 2·35—5·51; controlling for covariates, OR=1·27, 95%CI 1·17—1·39) at follow-up. For ever smoked cigarettes only, the impact of e-cigarette use was attenuated in the intervention (OR=1·83) compared to control (OR=4·53) condition. For ever smoked cigarettes and any recent tobacco smoking, the impact of e-cigarette use was attenuated among those with friends who smoked (OR=2·05 [ever smoked]; 1·53 [any tobacco use]) compared to those without friends who smoked (OR=3·32 [ever smoked]; 2·17 [any tobacco use]).
Conclusions: This is one of the first studies to show that e-cigarette use was robustly associated with measures of smoking over 24 months and the first to show an intervention to attenuate the relationship. Further research with a broader age-range of adolescents is required.