New York, (IANS): While electronic cigarettes (e-cigarettes) are generally assumed to be less harmful, new research has found that teenagers who use these cigarettes are more likely to smoke conventional cigarettes, cigars and hookahs over the next year compared with nonusers.

Electronic cigarettes, devices that deliver inhaled aerosol usually containing nicotine, are becoming increasingly popular, particularly among adolescents.

"Some teens may be more likely to use e-cigarettes prior to combustible tobacco because of beliefs that e-cigarettes are not harmful or addictive,” the study authors noted.

Adam Leventhal from University of Southern California, Los Angeles, and colleagues examined whether adolescents who reported ever using e-cigarettes were more likely to initiate the use of combustible tobacco (cigarettes, cigars, and hookah) during the subsequent year.

The study included 2,530 students from ten public high schools in Los Angeles who reported never using combustible tobacco at the beginning of the study in 2013, and completed follow-up assessments at six months in the spring 2014 or 12 months in the autumn of 2014.

At each time point, students completed self-report surveys on any use of combustible tobacco products.

The researchers found that e-cigarette users (222 students) were more likely to report use of any combustible tobacco product at the six-month follow-up (31 percent vs 8 percent) and at the 12-month follow-up (25 percent vs nine percent).

"These data provide new evidence that e-cigarette use is prospectively associated with increased risk of combustible tobacco use initiation during early adolescence," the study noted.

The findings appeared in JAMA: The Journal of the American Medical Association.