Use of electronic nicotine delivery systems and recent initiation of smoking among US youth.

Objectives: We assessed whether the prevalence of recent (within a year) initiation of cigarette smoking was associated with reports of ever using electronic delivery systems (ENDS) in the National Youth Tobacco Survey (NYTS) and whether the association varied by age.
Methods: Weighted cross-sectional analysis of use of ENDS, cigarette smoking, age at interview and age at initiation of smoking collected systematically through the 2011-2013 NYTS cycles.
Results: In multivariate analyses those who ever used ENDS were twice as likely as nonusers of ENDS to have tried cigarette smoking in the last year (multivariate PR: 2.3; 95 % CI 1.9, 2.7). This average hid significant variations by age: a 4.1-fold increase (95 %; 2.6, 6.4) among those 11-13 years of age, compared to a smaller increase among those 16-18 years: 1.4-fold (95 % CI 1.1, 1.8).
Conclusions: Use of ENDS by adolescents was associated with initiation of cigarette smoking in the last year. This association was stronger in younger adolescents.