Kids who experiment with e-cigarettes end up smoking tobacco about as much as teen smokers who never used the devices, according to a USC study in the journal Paediatrics.

"The findings show that e-cigs do nothing to deter the amount of combustible smoking in youth," said Jessica Barrington-Trimis, an assistant professor of preventive medicine at the Keck School of Medicine of USC and the study's lead author. "On the contrary, they increase the likelihood that vaping teens will start smoking."

The study is likely to add heft to a growing chorus seeking changes in regulation or industry practice for the nicotine delivery devices. Their popularity has surged while government and health officials warn of unintended consequences.

The e-cigarette market is expected to reach $44.6 billion worldwide in five years. 

Earlier this year, the FDA commissioner declared e-cigs and vaping an "epidemic" that threatens to undo gains in decreasing smoking rates, and ordered e-cigarette manufacturers to submit plans on reducing teen use.

"This study shows that tobacco control policies are needed to reduce adolescent use of e-cigs and prevent progression to more frequent tobacco use," Barrington-Trimis said.

The USC researcher and her colleagues surveyed 6,258 high schoolers from three studies, the Children's Health Study and Happiness and Health Study in Southern California, and the Yale Adolescent Survey study in Connecticut, about their vaping and smoking usage.

Participants were surveyed again about 12 months later.

Here's what researchers found:

• 7 percent of never-smokers started smoking
• 21 percent of e-cig users began smoking regular cigarettes
• The number of days that teens smoked in the past 30 days was similar for those who began smoking after using e-cigarettes or who began smoking without e-cigarettesTeens who were using both combustible and e-cigarettes were more likely to continue using both than to switch to vaping only.

Previously, researchers found that many of the kids who vaped started smoking cigarettes later.

"Paediatricians need to find a way to address this matter because e-cigarettes are not benign, and it's unlikely to stop there," said Barrington-Trimis. "A lot of people like to compare cigarette smoking to vaping and say, oh, vaping is safer. When you're talking about kids, and especially kids who might never have started smoking without vaping, it's definitely not safer than not using any tobacco products at all."

Barrington-Trimis said the study was unique because its large size allowed researchers to look beyond smoking initiation, and see what patterns emerged after a year.

Source: University of Southern California