Waterpipe smoking and subsequent cigarette and e-cigarette use: a cohort study.

Aim We tested the hypothesis that waterpipe smoking increases the likelihood to try conventional and electronic cigarettes. Methods In 2017 and 2018, 2752 German adolescents (mean age: 14.9 years), who had never tried conventional cigarettes or e-cigarettes, took part in a longitudinal survey with a 6-month observational period. Multiple regression analyses tested the association between waterpipe use at baseline and first experimentation with e-cigarettes at follow-up. The models adjusted for risk-taking propensity (sensation seeking and experimentation with alcohol and marijuana), age, sex, migration background, type of school and peer substance use. Results Some 381 adolescents (12.5% of the survey population) reported waterpipe smoking at baseline. The overall initiation rate during the 6 months was 4.9% (n=134) for conventional cigarettes and 10.5% (n=288) for e-cigarettes. Prior waterpipe smoking significantly predicted cigarette use (adjusted relative risk (ARR)=1.81, 95% CI 1.19–2.76), as well as e-cigarette use (ARR=3.29, 95% CI 2.53–4.28). In addition, a significant interaction between waterpipe use and sensation seeking was found (ARR=0.56, 95% CI 0.33–0.95), with waterpipe use being more predictive of later e-cigarette initiation for lower sensation-seeking individuals. Discussion Waterpipe use predicted both later cigarette and e-cigarette use independent of all other assessed risk factors, indicating that waterpipe use might be a risk factor on its own. The results suggest that the association was stronger for adolescents with a lower risk-taking propensity, which brings this group into focus for prevention efforts. However, further research is needed to understand whether these associations are causal.