Effects of e-cigarette use on cigarette smoking among U.S. youth, 2004-2018.

Objective: To determine if the declining trend in U.S. youth cigarette smoking changed after e-cigarettes were introduced, and if youth e-cigarette users would have been likely to smoke cigarettes based on psychosocial and demographic predictors of smoking.
Methods: An interrupted time series analysis was used for cross-sectional data from the 2004 to 2018 National Youth Tobacco Surveys (NYTS) to assess changes in cigarette and e-cigarette use over time. A multivariable logistic regression model used 2004-2009 NYTS data on psychosocial risk factors to predict individual-level cigarette smoking risk from 2011 to 2018. Model-predicted and actual cigarette smoking behavior were compared.
Results: The decline in current cigarette smoking slowed in 2014 (-0.75 [95% CI: -0.81, -0.68] to -0.26 [95% CI: -0.40, -0.12] percentage points per year). The decline in ever cigarette smoking accelerated after 2012 (-1.45 [95% CI: -1.59, -1.31] to -1.71 [95% CI: -1.75, -1.66]). Ever and current combined cigarette and/or e-cigarette use declined during 2011-2013 and increased during 2013-2014 with no significant change during 2014-2018 for either variable. The psychosocial model estimated that 69.0% of current cigarette smokers and 9.3% of current e-cigarette users (who did not smoke cigarettes) would smoke cigarettes in 2018.
Conclusions: The introduction of e-cigarettes was followed by a slowing decline in current cigarette smoking, a stall in combined cigarette and e-cigarette use, and an accelerated decline in ever cigarette smoking. Traditional psychosocial risk factors for cigarette smoking suggest that e-cigarette users do not fit the traditional risk profile of cigarette smokers.
(Published by Elsevier Inc.)