Nicotine may have some adverse health effects, but they are relatively minor, said Dr. Neal L. Benowitz, a professor of medicine at the University of California, San Francisco, who has spent his career studying the pharmacology of nicotine.

Another ingredient, propylene glycol, the vapor that e cigarettes emit whose main alternative use is as fake smoke on concert and theater stages is a lung irritant, and the effects of inhaling it over time are a concern, Dr. Benowitz said.

But Dr. Siegel and others contend that some public health experts, after a single minded battle against smoking that has run for decades, are too inflexible about e cigarettes. The strategy should be to reduce harm from conventional cigarettes, and e cigarettes offer a way to do that, he said, much in the way that giving clean needles to intravenous drug users reduces their odds of getting infected with the virus that causes AIDS.

Solid evidence about e cigarettes is limited. A clinical trial in New Zealand, which many researchers regard as the most reliable study to date, found that after six months about 7 percent of people given e cigarettes had quit smoking, a slightly better rate than those with patches.

The findings were intriguing but nothing to write home about yet, said Thomas J. Glynn, a researcher at the American Cancer Society.

In Britain, where the regulatory process is more developed than in the United States, researchers say that smoking trends are heading in the right direction.

Motivation to quit is up, success of quit attempts are up, and prevalence is coming down faster than it has for the last six or seven years, said Robert West, director of tobacco studies at University College London. It is impossible to know whether e cigarettes drove the changes, he said, but we can certainly say they are not undermining quitting.

The scientific uncertainties have intensified the public health fight, with each side seizing on scraps of new data to bolster its position. One recent study in Germany on secondhand vapor from e cigarettes prompted Dr. Glantz to write on his blog, More evidence that e cigs cause substantial air pollution. Dr. Siegel highlighted the same study, concluding that it showed no evidence of a significant public health hazard.

That Big Tobacco is now selling e cigarettes has contributed to skepticism among experts and advocates.

Cigarettes went into broad use in the 1920s and by the 1940s, lung cancer rates had exploded. More Americans have died from smoking than in all the wars the United States has fought. Smoking rates have declined sharply since the 1960s, when about half of all men and a third of women smoked. But progress has slowed, with a smoking rate now of around 18 percent.

Part of the furniture for us is that the tobacco industry is evil and everything they do has to be opposed, said John Britton, a professor of epidemiology at the University of Nottingham in England, and the director for the U.K. Center for Tobacco and Alcohol Studies. But one doesn t want that to get in the way of public health.

Carefully devised federal regulations might channel the marketing might of major tobacco companies into e cigarettes, cannibalizing sales of traditional cigarettes, Dr. Abrams of the Schroeder Institute said. We need a jujitsu move to take their own weight and use it against them, he said.

Dr. Benowitz said he could see a situation under which the F.D.A. would gradually reduce the nicotine levels allowable in traditional cigarettes, pushing smokers to e cigarettes.

If we make it too hard for this experiment to continue, we ve wasted an opportunity that could eventually save millions of lives, Dr. Siegel said.

Dr. Glantz disagreed.

I frankly think the fault line will be gone in another year, he said. The evidence will show their true colors.

Young using e-cigarettes smoke too, study finds – nytimes.com

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Middle and high school students who used electronic cigarettes were more likely to smoke real cigarettes and less likely to quit than students who did not use the devices, a new study has found. They were also more likely to smoke heavily. But experts are divided about what the findings mean.

The study s lead author, Stanton Glantz, a professor of medicine at the University of California, San Francisco, who has been critical of the devices, said the results suggested that the use of e cigarettes was leading to less quitting, not more.

The use of e cigarettes does not discourage, and may encourage, conventional cigarette use among U.S. adolescents, the study concluded. It was published online in the journal JAMA Pediatrics on Thursday.

But other experts said the data did not support that interpretation. They said that just because e cigarettes are being used by youths who smoke more and have a harder time quitting does not mean that the devices themselves are the cause of those problems. It is just as possible, they said, that young people who use the devices were heavier smokers to begin with, or would have become heavy smokers anyway.

The data in this study do not allow many of the broad conclusions that it draws, said Thomas J. Glynn, a researcher at the American Cancer Society.

The study is likely to stir the debate further over what electronic cigarettes mean for the nation s 45 million smokers, about three million of whom are middle and high school students. Some experts worry that e cigarettes are a gateway to smoking real cigarettes for young people, though most say the data is too skimpy to settle the issue. Others hope the devices could be a path to quitting.

So far, the overwhelming majority of young people who use e cigarettes also smoke real cigarettes, a large federal survey published last year found.

Still, while e cigarette use among youths doubled from 2011 to 2012, regular cigarette smoking for youths has continued to decline. The rate hit a record low in 2013 of 9.6 percent, down by two thirds from its peak in 1997.

The new study drew on broad federal survey data from more than 17,000 middle school and high school students in 2011 and more than 22,000 in 2012. But instead of following the same students over time which many experts say is crucial to determine whether there has been a progression from e cigarettes to actual smoking the study examined two different groups of students, essentially creating two snapshots.

Dr. Glantz says that his findings show that use of e cigarettes can predict who will go on to become an established smoker. Students who said they had experimented with cigarettes that is, taken at least one puff were much more likely to become established smokers if they also used e cigarettes, he said.

One of the arguments that people make for e cigarettes is that they are a way to cut down on the smoking of cigarettes, but the actual use pattern is just the opposite, he said.

But David Abrams, executive director of the Schroeder Institute for Tobacco Research and Policy Studies at the Legacy Foundation, an antismoking research group, said the study s data do not support that conclusion.

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, but that does not mean that gum is a gateway to smoking or makes it harder to quit, he said.

He argued that there were many possible reasons that students who experimented with e cigarettes were also heavier smokers for example, living in a home where people smoke, belonging to a social circle where smoking is more common, or abusing drugs or alcohol.

The study did have a bright spot Youths who used e cigarettes were more likely to plan to quit smoking. Dr. Abrams highlighted that finding, but said it was impossible to tell whether students who planned to quit actually did, because the data did not track this.