In a trial of e-cigarettes among Italian smokers with no desire to quit using tobacco at the outset, up to 13 percent of participants were not smoking regular cigarettes at all a year later.
Though the study was not billed as a smoking-cessation test, more than half of participants cut down on tobacco soon after they started using the e-cigarettes. And the percentage who quit smoking entirely by the end rivals results achieved with medications, the authors note in the journal PLOS ONE.
"I think the main message of the study is that we can use these products as an extraordinary tobacco control tool," Dr. Riccardo Polosa, the new study's senior author from the University of Catania, said.
"This really is the first clinical trial that's ever been reported on electronic cigarettes. There has been survey evidence and anecdotal reports, but this is the first serious study," said Dr. Michael Siegel, who studies e-cigarettes but wasn't involved in the new research.
E-cigarettes were first introduced in China in 2004. The battery-powered devices let users inhale nicotine-infused vapors, which don't contain the harmful tar and carbon monoxide in tobacco smoke.
While past studies have looked at the use of e-cigarettes, the new study is the first to follow hundreds of smokers for an entire year. It did not, however, compare the devices to traditional nicotine replacement therapies, such as gum or patches.
To see how many e-cigarette users would cut down or quit smoking cigarettes without any encouragement, the researchers recruited 300 people between June 2010 and February 2011. All were current smokers who stated they had no intention of quitting in the near future. Each participant was then randomized into one of three groups.
One group received e-cigarettes along with cartridges containing 7.2 milligram (mg) of nicotine. Another group also received the devices and 7.2 mg nicotine cartridges, but later in the study they were switched to 5.4 mg nicotine cartridges. And a third group got e-cigarettes and cartridges containing only tobacco flavor but no nicotine.
Each participant received enough supplies to last three months and went to regular checkups throughout the year.
At the end of the study, 13 percent of the group that first received the highest-dose nicotine cartridges was no longer smoking. That compared to 9 percent of those who were in the reduced-nicotine group and 4 percent in the group without nicotine.
Since there was no control group of smokers who got no e-cigarettes at all, it's hard to know how many would have quit smoking on their own by the end of a year, experts noted.
Siegel, a professor at the Boston University School of Public Health, said he would expect about 2 percent of the participants to quit within a year if they weren't involved in a study.
However, Polosa's team also found that between 9 and 12 percent of people in each of the nicotine-cartridge groups had reduced the amount they smoked by at least half.
"The study is very positive in that it shows if you smoke even a low- or medium-strength e-cigarette, you can get some increased quitting and decreased smoking," Dr. Murray Laugesen, a tobacco and nicotine researcher who was not involved with the new study, said.
"It also has to be acknowledged that these are good results in people who had no intention of quitting," said Laugesen, a public health medicine specialist at Health New Zealand Ltd in Christchurch. He is also involved in an e-cigarette clinical trial and hopes to present the results in September.
Siegel said that what's attractive about e-cigarettes is they can not only provide the nicotine that smokers crave without other harmful substances, they allow people to mimic their traditional smoking behavior.
Researchers said that's one reason why e-cigarettes might turn out to be a better form of nicotine replacement therapy than patches and gums, but there's no data yet to prove it.
"I think that's why they… found the people who actually got no-nicotine electronic cigarettes had some sort of quitting behavior… But obviously the people who got the nicotine and the high dose of nicotine did the best. Clearly having the nicotine and device structure is ideal," Siegel said.
But he cautioned that more research is needed - especially on the long-term safety of e-cigarettes and how the devices stack up against traditional smoking cessation methods.
"My advice to people is to try the traditional therapy first. But I think electronic cigarettes are for people who have tried and failed nicotine replacement therapy, which is, sadly, most people," Siegel added.