This year the Monitoring the Future Study, which I mentioned yesterday in connection with marijuana use by teenagers, asked about electronic cigarettes for the first time. It found that "more teens use e-cigarettes than traditional, tobacco cigarettes or any other tobacco product." Whether you see that news as cause for alarm depends on whether you view e-cigarettes as a potentially lifesaving alternative to conventional cigarettes or as a menace to the youth of America. That, in turn, depends on how calmly you consider the evidence.

In the Monitoring the Future (MTF) survey, 17.1 percent of 12th-graders, 16.2 percent of 10th-graders, and 8.7 percent of eighth-graders reported using e-cigarettes in the previous month. By comparison, the CDC's National Youth Tobacco Survey (NYTS) last year put the prevalence of past-month e-cigarette use among all high school students at 4.5 percent. Although the two surveys are not directly comparable, the gap suggests that past-month e-cigarette use by teenagers, which according to the NYTS tripled between 2011 and 2013, continues to rise. But at the same time, both surveys show that smoking among teenagers continues to fall. In fact, the rates of past-month cigarette smoking among eighth-graders, 10th-graders, and 12th-graders in the MTF survey—4 percent, 7.2 percent, and 13.6 percent, respectively—are lower than ever before in the history of the study, which began in 1975. Furthermore, as Bill Godshall of Smokefree Pennsylvania points out, the drops in past-month cigarette smoking between 2013 and 2014—11 percent, 21 percent, and 17 percent, respectively—are the largest such decreases ever seen.

Given these data, it hardly seems reasonable to conclude that more vaping means more smoking. Yet that is what anti-smoking activist Stanton Glantz claims. "There's no question that e-cigarettes are a gateway to smoking," he recently told USA Today. The story cites recent studies of e-cigarette use by teenagers in Hawaii and Connecticut, neither of which proves Glantz's claim.

The Hawaii survey, conducted last year, found that 18 percent of high school students had used e-cigarettes in the previous month, which is four times the nationwide rate indicated by the 2013 NYTS. At the same time, however, the past-month smoking rate in Hawaii was just 7 percent, compared to a national average of 12.7 percent in 2013, per the NYTS. So in Hawaii, an unusually high rate of e-cigarette use by teenagers coincides with an unusually low smoking rate, and this supposedly shows that "e-cigarettes are a gateway to smoking."

The Connecticut study, which included a survey of students at four high schools, two middle schools, and a college, found that 21 percent of them had ever tried e-cigarettes. The study does not say how many had used e-cigarettes in the previous year or month. But as in Hawaii, the past-month smoking rate was quite low: 7 percent, about half the national average for high school students. Again, this does not look like evidence that the rising popularity of e-cigarettes is attracting teenagers to the conventional kind.

If anything, the fact that vaping and smoking rates among teenagers are moving in opposite directions is consistent with the idea that e-cigarettes are replacing combustible cigarettes among people who otherwise would be smoking. Godshall cites additional evidence from the MTF survey in support of that hypothesis:

Among [the] 33.8% of 12th graders who reported ever smoking a cigarette, MTF found that during the "past 30 days" 16% reported no use of cigarettes or e-cigs, 4.6% reported exclusive e-cig use, 7.3% reported dual use of cigarettes and e-cigs, and just 5.9% reported exclusive cigarette smoking. Among [the] 21.9% of 10th graders who reported ever smoking a cigarette, MTF found that during the "past 30 days" 10.0% reported no use of cigarettes or e-cigs, 4.9% reported exclusive e-cig use, 4.3% reported dual use of cigarettes and e-cigs, and just 2.7% reported exclusive cigarette smoking. Among [the] 13.3% of 8th graders who reported ever smoking a cigarette, MTF found that during the "past 30 days," 6.6% reported no use of cigarettes or e-cigs, 2.2% reported exclusive e-cig use, 2.2% reported dual use of cigarettes and e-cigs, and just 2.3% reported exclusive cigarette smoking.

These patterns suggest that e-cigarettes may be helping some adolescent cigarette smokers cut back or quit. Even when teenagers try e-cigarettes first, some of them might otherwise have smoked the conventional kind. The upshot in both cases would be the same: less smoking and less tobacco-related disease, something anti-smoking activists like Glantz supposedly want.

New York Times science reporter Sabrina Tavernise treats the claims of Glantz and other opponents of vaping with appropriate skepticism (emphasis added):

Health advocates say the trend [in] e-cigarette use is dangerous because it is making smoking seem normal again. They also worry it could lead to an increase in tobacco smoking, though the new data do not show that…. E-cigarettes have split the public health world, with some experts arguing that they are the best hope in generations for the 18 percent of Americans who still smoke to quit. Others say that people are using them not to quit but to keep smoking, and that they could become a gateway for young people to take up real cigarettes. But that does not seem to be happening, at least so far. Daily cigarette use among teenagers continued to decline in 2014, the survey found, dropping across all grades by nearly half over the past five years. Among high school seniors, for example, 6.7 percent reported smoking cigarettes daily in 2014, compared with 11 percent five years ago.

Tavernise also notes that "most experts agree that e-cigarettes are far less harmful than traditional cigarettes." That is why the crucial question, in assessing the "public health" impact of e-cigarettes, is whether they compete with tobacco cigarettes or somehow expand the market for them. The evidence so far clearly supports the former view.