E-cigarettes - thought by some to be responsible for a decline in youth cigarette smoking - are actually attracting a new population of adolescents who might not otherwise have smoked tobacco products, according to a new UC San Francisco study.

In the first national analysis of the impact of e-cigarettes on trends in youth smoking in the United States, UCSF researchers did not find evidence that e-cigarettes have caused youth smoking to decline.

In fact, combined e-cigarette and cigarette use among adolescents in 2014 was higher than total cigarette use in 2009, according to the study.

The authors concluded that the low-risk youth in the study, who went on to smoke regular cigarettes, may not have used nicotine at all if e-cigarettes did not exist.

The study will be published online January 23, 2017 in Pediatrics as well as the February print issue of the journal.

"We didn't find any evidence that e-cigarettes are causing youth smoking to decline," said lead author Lauren Dutra, a former postdoctoral fellow at the UCSF Center for Tobacco Control Research and Education and current social scientist at RTI International, a not-for-profit research organization based in North Carolina.

"While some of the kids using e-cigarettes were also smoking cigarettes, we found that kids who were at low risk of starting nicotine with cigarettes were using e-cigarettes," Dutra said. "Recent declines in youth smoking are likely due to tobacco control efforts, not to e-cigarettes."

The national analysis builds on several previous studies that have reported that adolescents who start with e-cigarettes are more likely to subsequently smoke traditional cigarettes.

In August 2016, the U.S. Food and Drug Administration restricted e-cigarette purchases to adults ages 18 and older (California set the age to 21).

The FDA also will require a warning label on e-cigarettes, starting August 2018, regarding the addictive nature of nicotine.

However, the FDA's ruling does not regulate advertising or flavours, and e-cigarettes continue to be sold in flavours that appeal to youth.

In the new UCSF study, the researchers examined survey data from more than 140,000 middle and high school students who completed the CDC's National Youth Tobacco Survey between 2004 and 2014.

The authors found that cigarette smoking among U.S. adolescents declined during that decade, but did not decline faster after the advent of e-cigarettes in the U.S. between 2007 and 2009.

The authors also performed an in-depth analysis of the psychosocial characteristics of e-cigarette users.

Research has established that smokers tend to display certain characteristics that non-smokers are less likely to show, such as a tendency to live with a smoker or to wear clothing that displays a tobacco product logo.

The smokers in the national youth survey displayed these characteristics, but the adolescents who were only using e-cigarettes displayed few of these qualities.

"E-cigarettes are encouraging - not discouraging - youth to smoke and to consume nicotine, and are expanding the tobacco market," said senior author Stanton A. Glantz, PhD, UCSF professor of medicine and director of the UCSF Center for Tobacco Control Research and Education.

The new results are consistent with a similar study of youth in California conducted last year by researchers at the University of Southern California and also published in Pediatrics.

Those researchers also found that adolescents who used e-cigarettes - but not cigarettes - displayed few of the risk factors commonly found among cigarette smokers.

In combination, the two studies suggest that "e-cigarettes are attracting low-risk youth," the UCSF scientists said.

Source: Pediatrics