A
study reported today in The Journal of the American Medical
Association claims to present evidence that “e-cigarette
use is aggravating rather than ameliorating the tobacco epidemic
among youths.” The authors, Lauren Dutra and Stanton Glantz of the
Center for Tobacco Research and Education at the University of
California in San Francisco, claim their results “suggest that
e-cigarettes are not discouraging use of conventional cigarettes.”
They add that their findings “call into question claims that
e-cigarettes are effective as smoking cessation aids.” But as
Boston University public health professor Michael Siegel
observes on his tobacco policy blog, Dutra and Glantz “make one
of the most cardinal errors in all of epidemiology” by ignoring
“the principle that ‘correlation does not equal causation.'”
Dutra and Glantz’s study is based on data from the National
Youth Tobacco Survey, the same study the U.S. Centers for Disease
Control and Prevention (CDC) cited last September in
sounding the alarm about the recent increase in e-cigarette use
among teenagers. The CDC neglected to mention that
smoking fell as vaping rose, a trend that might have cast doubt
on its warnings that e-cigarettes are a gateway to the real thing.
Dutra and Glantz try to make that fear plausible by looking at
associations between e-cigarette use and smoking in survey results
from 2011 and 2012. They find that “use of e-cigarettes was
associated with higher odds of ever or current cigarette smoking,
higher odds of established smoking, higher odds of planning to quit
smoking among current smokers, and, among experimenters, lower odds
of abstinence from conventional cigarettes.” In other words,
e-cigarette users were more likely to be smokers, tended to smoke
more, and were less likely to have stopped smoking, even though
they were more likely to say they would like to quit.
The problem, of course, is that a cross-sectional study like
this one does not tells us which came first: vaping or smoking.
Dutra and Glantz concede that “the cross-sectional nature of our
study does not allow us to identify whether most youths are
initiating smoking with conventional cigarettes and then moving on
to (usually dual use of) e-cigarettes or vice versa.” If teenagers
try e-cigarettes as a substitute for the conventional kind, it is
hardly surprising that vapers are more likely to be smokers. In
both 2011 and 2012, half of the current (past-month) e-cigarette
users were also current smokers, which is consistent with the
hypothesis that vaping is a strategy for cutting down or quitting.
It is plausible that smokers with a strong attachment to cigarettes
would be especially likely to try that strategy, which could
explain why e-cigarette users smoked more and were less likely to
have abstained from tobacco.
David Abrams, executive director of the Legacy
Foundation’s Schroeder Institute for Tobacco Research and
Policy Studies, made that point in an interview with The New
York Times. “I am quite certain that a survey would find
that people who have used nicotine gum are much more likely to be
smokers and to have trouble quitting,” he
said, “but that does not mean that gum is a gateway to
smoking or makes it harder to quit.” Thomas Glynn of the American
Cancer Society likewise cautioned that “the data in this study do
not allow many of the broad conclusions that it draws.”
Even if we knew that some teenagers start with vaping and move
on to smoking, that would not necessarily mean that e-cigarettes
made them more likely to smoke. We still would not know what would
have happened in the absence of e-cigarettes. Would those same
teenagers have started smoking anyway, or did the experience of
vaping somehow prime them to like a habit that otherwise would not
have attracted them? The same sort of question comes up in
discussions of marijuana’s purported role as a “gateway” to
other drugs. In both cases, symbolism and emotion carry more weight
than evidence and logic.
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