The popularity of e-cigarettes among teenagers now eclipses that of traditional cigarettes, the use of which has fallen to the lowest level in years.
In the latest study, researchers analyzed data from a national sample of nearly 700 nonsmokers who were between ages 16 and 26 in 2012, and again in 2013. All of them said "definitely no" when they were asked if they would try a cigarette offered by a friend or believed they would smoke a cigarette within the next year.
Only 16 of the participants used e-cigarettes when they were initially surveyed, but six of them had progressed to cigarette smoking by the next year, or about 38 percent. By contrast, only 10 percent of the youths who were not e-cigarette users started smoking traditional cigarettes.
The study was conducted by the University of Pittsburgh Center for Research on Media, Technology and Health and the Dartmouth-Hitchcock Norris Cotton Cancer Center.
In the past, few studies looked at whether e-cigarette users who initially did not smoke were at risk for taking up both the use of e-cigarettes and traditional cigarettes, or the exclusive use of cigarettes. Previous studies could not determine whether e-cigarette use preceded cigarette use, researchers said. Those studies also looked at different youngsters over different time periods.
The latest study analyzed the same individuals over time.
"This is the first longitudinal, national study to show that e-cigarette use among youth directly leads to regular cigarette use, even among people who insist at baseline that they never will smoke regular cigarettes," said lead author Brian Primack, who is assistant vice chancellor for health and society at Pittsburgh's Schools of the Health Sciences. "It is also the first to include young adults, as opposed to strictly teenagers."
Researchers said one limitation was the relatively small number in the sample size. The findings need to be replicated with larger samples. Even so, after controlling for well-known risk factors, such as age, sex, socioeconomic status and risk-taking, "we think the effect is real," said Samir Soneji, an assistant professor at the Dartmouth Institute for Health Policy and Clinical Practice and one of the authors.
E-cigarettes accelerate the progression to traditional cigarette smoking, he said.
The quandary for public health officials is this, he said. "Are they more dangerous for kids than they are helpful for adults who are trying to quit smoking?"