Actor Leonardo DiCaprio is seen puffing away on his electronic cigarette and blowing out rings of smoke between takes while filming on his last day for new movie 'The Wolf of Wall Street' at Rao's Restaurant in East Harlem, New York. [Photo/icpress]

For those who were still smoking in 2012, using e-cigarettes also did not appear to change how many traditional cigarettes people smoked per day.

The researchers note that the small number of participants who reported using e-cigarettes may have limited their ability to detect a link between quitting smoking and using the device.

Dr Michael Siegel, who was not involved with the new research, says that the new study had several design flaws, including that the researchers did not know why some of the participants tried e-cigarettes or how long they had used them. Siegel is an expert on community health at Boston University School of Public Health and has studied e-cigarette research.

By comparing people who smoked regular cigarettes and those who smoked e-cigarettes, the researchers are assuming "that the groups are exactly equivalent in terms of their motivations and their levels of addiction to cigarettes", Siegel says. "You can't make those assumptions. You're not dealing with comparable groups."

In an e-mailed statement, Grana and fellow researchers acknowledged that they did not have information on the participants' motivations to use e-cigarettes, but said their analysis took into account other factors known to be linked to quitting smoking, such as their stated intention to quit and how many cigarettes they already smoked each day.

"These factors may also reflect motivations to use e-cigarettes, as e-cigarettes are frequently marketed and perceived as cessation aids," they write. "While these factors predicted quitting as expected, we found that e-cigarette use did not predict quitting."

Siegel also points out that only about 8 percent of the people surveyed said they had any intention to quit smoking within the next month. He hopes people will reserve judgment on e-cigarettes until randomized controlled studies—considered the "gold standard" of medical research—are published.

"We need solid data that's based on solid science before we make decisions," he says. "I hope no one would take this research letter and make any conclusion based on it."

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