A recent study found a connection between smoking and use of e-cigarettes among adolescents. Published Thursday in the journal JAMA Pediatrics, the study found that among those who smoked, those adolescents who also used e-cigarettes were less likely to give up smoking than those who did not use them.

The authors of the study, Lauren Dutra and Stanton Glantz, found that "the use of e-cigarettes does not discourage, and may encourage, conventional cigarette use among U.S. adolescents."

Not everyone is convinced by the results of the study. Dr. Michael Siegel, professor of community health sciences at Boston University School of Public Health, said that while the study shows a connection between e-cigarette use and smoking, it did not prove that e-cigarettes led to smoking.

"The authors seem to have an axe to grind," he said. "I could equally argue that what this study shows is that people who are heavy smokers are attracted to e-cigarettes because they are looking to quit."

The study was conducted by the University of California San Francisco's Center for Tobacco Control Research and Education and funded by the National Cancer Institute.

For their study, the researchers surveyed 17,353 middle and high school students in 2011, and 22,529 people in 2012 as part of the National Youth Tobacco Survey. Adolescents who reported ever using e-cigarettes or currently using them had a greater chance of trying regular cigarettes, being a current cigarette smoker or smoking on a regular basis. Among those who had used tobacco cigarettes, trying an e-cigarette was connected to being an established smoker. The study also found that teens who used e-cigarettes had a greater likelihood of wanting to quit smoking the next year, but were also less likely to completely abstain from cigarettes.

The study did not determine whether teens started with e-cigarettes and moved to regular cigarettes, or vice versa. It comes as the U.S. Food and Drug Administration prepares for regulatory control over e-cigarettes, which had sales of almost $2 billion last year.

Rates of adult smoking have fallen to 18 percent from 43 percent in 1965. More than 3,200 people a day under age 18 try their first cigarette, according to a recent government report. Between 2011 and 2012 young people's use of e-cigarettes doubled.

Advocates of e-cigarettes say that the vapor found in them is less harmful than regular cigarette smoke. However, information on the long-term safety of e-cigarettes is limited. Several cities, including Chicago, New York, Boston and Los Angeles have banned the use of e-cigarettes in bars, restaurants, nightclubs and other public places.