(See: Miech R, Patrick ME, O’Malley PM, Johnston LD. E-cigarette use as a predictor of cigarette smoking: results from a 1-year follow-up of a national sample of 12th grade students. Tobacco Control. http://dx.doi.org/10.1136/tobaccocontrol-2016-0532910).
The study involved a one-year follow-up of 347 high school seniors who were surveyed at baseline in 2014 and at follow-up in 2015. At baseline, they were classified as recent vapers (used an e-cigarette in the past 30 days) or non-vapers. At follow-up, smoking initiation was defined as having smoked a cigarette in the past year.
In the key analysis, smoking initiation (smoking a cigarette in the past year) was compared between recent vapers (used an e-cigarette in the past 30 days) and non-vapers who had never smoked at the time of the baseline survey. The paper reports that the rate of smoking initiation was 31% among the recent vapers and 7% among non-vapers. In an adjusted analysis, recent vapers were 4.8 times more likely than non-vapers to initiate smoking during the follow-up period.
The paper concludes that “vaping is a one-way bridge to cigarette smoking among youth.”
The Rest of the Story
At first glance, this paper appears to demolish the claim that vaping is not a known gateway to youth smoking. The conclusion that is drawn is a sweeping one: e-cigarettes are a one-way bridge to cigarette smoking among youth. If this conclusion is true, then I believe e-cigarettes are not a tenable harm reduction strategy because the benefits of adults quitting using e-cigarettes would be offset by a substantial increase in youth becoming addicted to smoking and possibly suffering life-long health effects, disease, disability, and premature death.
So am I going to renounce my earlier conclusions (that there is no evidence vaping causes kids to start smoking)?
Perhaps, but not without a closer look at the study.
To be a valid conclusion, there must not be a plausible, alternative explanation for the study findings. The paper does not present any alternative explanations. But this doesn’t mean that there isn’t one.
In fact, there is a very plausible (and in fact, highly likely) alternative interpretation of these findings:
Experimenting with e-cigarettes is a sensitive marker of substance-related, risk-taking behavior in general, which strongly predisposes a youth to trying cigarettes.
What could easily explain the observed findings is that youth who experiment with e-cigarettes are also more likely to experiment with other substances, including cigarettes. Therefore, of course you are going to find a higher rate of cigarette experimentation among youth who have already experimented with electronic cigarettes. This should come as a surprise to no one.
The observed relationship between e-cigarette experimentation and cigarette experimentation could well be a spurious one, confounded by an underlying predisposition to substance-related, risk-taking behavior. Importantly, the study did not make any attempt to control for any measures of risk-taking behavior. Moreover, the study did not even control for underlying susceptibility to smoking.
There are two additional and related factors that cast serious doubt on the study’s conclusion.
First, the exposure variable – recent vaping – was defined as having tried even one e-cigarette in the past month. All we know about the baseline “vapers” is that they had taken a puff on an e-cigarette in the past month. We do not know that they were regular vapers. We do not know that they had become addicted to nicotine or to vaping. We don’t even know that they had tried vaping more than once in their entire life! So to conclude that this study demonstrates that vaping is a one-way bridge to smoking is not warranted.
Second, the outcome variable – smoking initiation – was defined as having tried even one cigarette in the past year. All we know about the smoking initiators is that they had taken a puff on a cigarette in the past year. We don’t even know that they had tried more than one cigarette in the past year. So to conclude that vaping is a bridge to smoking based on this definition is not warranted.
The question that arises is why the study did not examine whether frequent vapers were more likely to progress to regular smoking (or at very least, current or established smoking). According to the paper, the sample size was not large enough to allow such an analysis. But that raises the question: If the sample size was not large enough to allow an analysis of frequent vapers, was it large enough to allow an analysis of all vapers? And most critically, how many youths were there who were nonsmoking, recent vapers at baseline who tried a cigarette in the next year? After all, this is the sample upon which the entire conclusion of the study is based.
So I took a closer look at the study – well, not the actual study because the sample size of baseline nonsmokers who had recently vaped is not reported anywhere in the study. You have to go to a separate, online appendix to find this out.
So take a guess: How many youths is the sweeping conclusion of this paper based on? (i.e., how many nonsmoking, recent vapers at baseline progressed to having tried a cigarette at follow-up?)
If you guessed E (9) ...
… then you are wrong.
The correct answer is none of the above. The total number of nonsmoking, recent vapers who tried a cigarette in this study appears to be just 4!
So you mean to tell me that the sweeping conclusion of this paper – that vaping is a one-way bridge to smoking – is based on 4 youth? Moreover, on 4 youth about whom all we know is that they tried an e-cigarette during the month prior to the baseline survey and then tried a cigarette in the following year. That hardly seems like a sufficient sample of youth upon which to rely to formulate national policy.
In fact, there were apparently only 13 nonsmokers who were recent vapers in the entire study of 347 youth. That itself should tell you something. Namely, that it is very difficult to find nonsmokers who vape with any significant frequency. In other words, e-cigarette experimentation is not any kind of significant bridge to youth smoking because it doesn’t even appear to be a bridge to regular or frequent vaping.
The rest of the story is that far from providing evidence that vaping is a one-way bridge to cigarette smoking among youth, this study provides further evidence that e-cigarette experimentation among nonsmoking youth doesn’t even appear to be a bridge to regular vaping. It is very difficult to find nonsmoking youth who experiment with e-cigarettes and then progress to become frequent vapers. In fact, it’s such a rare phenomenon that this study failed to achieve a high enough sample size to even analyze the rate at which these nonsmoking frequent vapers progressed to smoking. That itself is really the key finding of the paper.
This story illustrates why you have to be very careful in reading and interpreting the scientific literature. If you didn’t look at the supplemental material, which was not part of the article itself, you would never even be aware that the sweeping conclusions of this study were based on 4 kids.
All I can say is that when the FDA commissioner signs his first order putting a vape shop out of business, these 4 kids should be invited to the signing ceremony. Because it’s based on those 4 kids that vaping opponents apparently would like us to formulate national smoking policy.
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