By Amy Norton
MONDAY, Jan. 23, 2017 (HealthDay News) -- There's no evidence that e-cigarettes are driving down teen smoking -- and, in fact, they may be drawing in kids who otherwise would never have smoked, a new study suggests.
Researchers said the findings add to concerns about teenagers' use of e-cigarettes.
E-cigarettes are battery-powered devices that deliver nicotine -- along with flavoring and other chemicals -- through a vapor rather than tobacco smoke. They are often marketed as a "safer" alternative to smoking, and a bridge toward quitting.
But little is actually known about their health effects, according to the U.S. National Institutes of Health.
In recent years, the devices have been soaring in popularity among U.S kids. A federal report found that between 2013 and 2014, e-cigarette use tripled among high school and middle school students nationwide.
Still, cigarette smoking has continued to decline. And some have argued that the rise in kids' e-cigarette use might actually be feeding the decrease in their smoking rate, said Lauren Dutra, the lead researcher on the new study.
Based on her findings, however, she said that's not the case.
"We found no evidence to support that idea," said Dutra, who was a fellow with the University of California, San Francisco's Center for Tobacco Control Research and Education at the time of the study.
In fact, the study found, many kids who used e-cigarettes had never smoked -- and were actually "low risk" for starting.
"These aren't the kids we would normally expect to take up smoking," said Dutra, who is now a social scientist with the non-profit research group RTI International.
The study findings are based on an ongoing federal survey tracking tobacco use among U.S. kids in grades six through 12.
Overall, students' smoking rates dropped between 2004 and 2014, from nearly 16 percent to just over 6 percent. The decline was steady, with no signs of speeding up after 2009 -- when e-cigarettes came onto the scene.
If the devices really were driving kids away from cigarettes, Dutra said, you'd expect to see an acceleration in the smoking decline.
Instead, the researchers said they found evidence that e-cigarettes are attracting kids who would be unlikely to use tobacco.
The number of U.S. kids using e-cigarettes alone rose during the latter part of the survey period. By 2014, 6.5 percent of students said they'd ever used the devices, but had never smoked.
And, the study found, most of those kids did not have the risk factors that are usually linked to cigarette smoking -- such as living with a smoker, or thinking that smoking makes a person "look cool."
But if e-cigarettes contain no tobacco, what is the harm?
"One is that kids who use e-cigarettes are more likely to start smoking cigarettes," said Thomas Wills, a professor at the University of Hawaii Cancer Center, in Honolulu.
"It is clear that e-cigarettes act as a gateway to smoking," added Wills, who wrote an editorial published with the research.
Plus, he said, some studies have linked e-cigarettes to asthma in teenagers. It's not clear why, but it's potentially related to "combustion products" from the devices' flavorings and propylene-glycol base, Wills said.
And, of course, e-cigarettes contain nicotine -- a highly addictive drug, both Wills and Dutra pointed out.
The report was published online Jan. 23 in the journal Pediatrics.
A separate study in the same issue of the journal pointed to other concerns.
The study by Zewditu Demissie, of the U.S. Centers for Disease Control and Prevention, and colleagues found that U.S. kids who used e-cigarettes alone showed elevated rates of "risky" behaviors -- such as having multiple sexual relationships or abusing marijuana or prescription painkillers.
Among the teens in the study who "vaped," rates of those health risks were not as high as smokers' were. But they were higher compared with kids who used no tobacco-related products.
However, the study doesn't prove that e-cigarettes cause teenagers to take health risks, the researchers wrote.
Wills said, on one hand, e-cigarettes may attract kids who are somewhat drawn to "risky things."
But, he added, studies do suggest that e-cigarettes can encourage at least one unhealthy habit: Smoking.
Last year, the U.S. Food and Drug Administration banned e-cigarette sales to minors -- after many U.S states already had. But Dutra said that's unlikely to be enough.
"Cigarettes have been restricted to people 18 and over for a long time," she noted, "but kids still get them."
E-cigarettes appeal to kids, Dutra said, because they are flavored, with enticing tastes such as "birthday cake."
"They don't taste like an ashtray," Dutra said. "They taste good."
She noted that regulators have taken no steps to address the devices' "kid-friendly" flavors, TV ads or health claims.
If e-cigarettes do encourage some kids to try cigarettes, then why are smoking rates still going down? According to Dutra, the most recent federal figures -- from 2015 -- suggest the decline is plateauing, and smoking rates may even be ticking up slightly among high school kids.