Authors: David T Levy et al.

In 2018, the National Academies of Sciences, Engineering and Medicine (NASEM) released a report that examined the relationship between e-cigarette use and traditional, combustible cigarette use among young people. Essentially, the findings of the report supported the argument that e-cigarettes function as a gateway to combustible cigarette use. However, such a conclusion is contradicted by long-term population trends, which show that the rate of smoking is decreasing as the rate of vaping increases, an observation noted in the NASEM report.

This disagreement in data prompted David Levy et al. to reevaluate the relationship between vaping and smoking initiation among young people. The resulting study used multiple nationally representative datasets to assess the temporal relationship (that is, to determine which came first) between vaping and smoking initiation among youth.

In doing so, the authors established the average annual change in smoking prevalence from 2004 to 2013 to determine the long-term trend, which they used to extend the linear trend through 2017. Next, using the predicted value from the established, decreasing trend in smoking (from 2004-2017), they created a time-series model of smoking prevalence that accounts for the years where vaping was not prevalent (prior to 2014) and examines how the trend in youth smoking has changed since the introduction of e-cigarettes. As a result, several interesting findings emerge.

First, 2014 is the first year in which vaping became popular among youth and young adults. For this reason, data sources for years before 2014 were limited and inconsistent. This is important because an earlier, similar study attempted to draw conclusions about a possible temporal relationship between vaping and smoking among young people, however, that study only included data from 2004 to 2014. Accordingly, any change they found in the long-term smoking rate is likely unrelated to e-cigarette use. Levy et al.’s use of the additional and more relevant years of data therefore paint a more accurate picture of the true association between e-cigarette use and youth smoking trends.

Second, it is noteworthy that, for the vast majority of data sources Levy et al. analyzes, the prevalence of smoking among young people decreased more than predicted by long-term trends after vaping became prevalent in 2014. And, what’s more, the few data sources that did not see an acceleration of the downward trend in smoking showed no impact at all of vaping on the established trend in smoking. This suggests that the popularity of vaping affected the youth smoking rate by diverting young people from combustible use. That is, young people who would have otherwise smoked combustible cigarettes may be using e-cigarettes instead.

What’s more, the model generalizes across several national datasets that measure smoking behavior in the United States (MTF, NYTS, YRBS, NSDUH, NHIS), which means that it provides consistent and valid results when applied to multiple datasets with different characteristics. In fact, in the majority of datasets used, the introduction of vaping accelerated the decline of cigarette use. This strongly suggests that vaping does not increase cigarette use on the population level.

Moreover, models that result in the same findings using more than one data source are considered to be more representative of the true association between two events. Levy et al. tests the model using five data sources and twenty-two measures (populations) and found that downward deviation from predicted smoking rates was highest among 10th graders and lowest in 22-24-year-olds. This suggests that reductions in smoking as a result of vaping are most evident among older teens. Put simply, Levy et al. finds that vaping actually appears to reduce combustible cigarette use in youth populations.

Overall, this study presents a straight-forward, simple model of the change in smoking prevalence after vaping became established in the U.S. population. Since we do not know the nature of the association between vaping and smoking among youth, it is important that we continue to evaluate using different data sources and methods. It is also important that studies are updated when new data is presented. Levy et al. is an impactful study that lays groundwork for additional research on the impact of vaping on smoking initiation and use; however, the authors are correct in their conclusion that the results should be interpreted carefully due to the simplicity of the model.

Levy et al. provides a methodologically sound article that adds to the growing body of literature on the casual association between vaping and smoking. They address a statistically important conundrum: if vaping is associated with future smoking, why are smoking rates still declining as vaping rates are increasing? Answering this question will have a profound effect on the way legislators and public health leaders should approach youth vaping.