INTRODUCTION Though smoking is a public health problem the use of e-cigarettes has been associated with a reduction in smoking in developed countries. However, public health experts have raised concerns about the association of e-cigarette use with an increase in traditional cigarette smoking in adolescents. Reviewlevel evidence is generally supportive of this concern, but as it is mainly based on studies from the USA we investigated if e-cigarette use is associated with traditional cigarette smoking in adolescents (aged 10-19 years) in the UK. METHODS We conducted a systematic review of empirical studies. Databases (PubMed, Medline via ProQuest, CINAHL and SCOPUS) were searched between January 2005 and May 2018 using search terms based on the concepts: adolescents, traditional cigarette smoking, e-cigarettes, and UK. Using predefined inclusion and exclusion criteria, a total of eight studies (involving 73076 adolescents) were included in this review. Three of the included studies were eligible to be combined in a meta-analysis. The CASP appraisal tool was used to assess study quality while risk of bias was assessed using ROBINS-I. RESULTS Studies included in the meta-analysis showed that adolescents who use e-cigarettes are up to six times more likely to smoke traditional cigarettes. Furthermore, results showed that traditional cigarette smoking can also precede e-cigarette use in adolescents and there was increased likelihood of an increase in initial product use (e-cigarette or traditional cigarette) when the alternate product was initiated. CONCLUSIONS Public health policy makers in the UK still need clear conclusions about the effects and safety of e-cigarettes. AFFILIATION

No abstract