Recent studies have found that teenagers who use e-cigarettes are more likely to start smoking tobacco cigarettes. But it turns out it’s not just whether teens vape that predicts whether they'll start smoking later: Frequent vaping or using flavored e-cigs is also associated with an elevated risk of becoming a regular cigarette smoker, two new studies show.

To find out if the frequency of vaping was tied to the risk of becoming a smoker, Adam Leventhal, Ph.D., director of the Health, Emotion and Addiction Laboratory at the University of Southern California, and his colleagues surveyed about 3,300 California 10th graders. The teens answered questions about whether they used e-cigarettes, and if so, how often. Six months later, the researchers followed up.   

“We found that the more you vape, the more likely you were to be a cigarette smoker six months later, and the more likely you were to be smoking multiple cigarettes per day,” says Leventhal, whose study was published in JAMA.

The difference was stark. At the time of the follow-up, less than 1 percent of those who had never used e-cigs and only about 5 percent of those who were infrequent users (vaping just one or two days during that month) had become frequent cigarette smokers, which the study defined as people who had smoked at least three times in the past 30 days. In contrast, nearly 20 percent of the teens who had been vaping three or more days a month were—at the time of the follow-up—frequent cigarette smokers (defined as having at least two cigarettes on the days they smoked).

While it’s too early to generalize from a study of 3,300 California 10th graders, the results suggest that the frequency of vaping may be a key risk factor in a teen’s decision to take up smoking later.

The Trouble with Flavored E-Cigs

Experts have long suspected that flavored e-cigs may be especially attractive to young people. They're available in more than 7,000 flavors, with plenty of kid-friendly options like Candy Crush, Cotton Candy, and Gummy Bear.

And now a new study published in the journal Pediatrics finds that middle and high school students who use flavored e-cigs say that they are more likely to try smoking traditional cigarettes than their peers who don't vape, or who vape using unflavored e-cigs. (The researchers did not follow up to see whether the students had gone from considering trying cigarettes to actually doing it.)

The results are based on data from roughly 21,500 middle and high school students nationwide, who participated in the 2014 National Youth Tobacco Survey.

Those who used flavored e-cigs were nearly six times as likely to say they would try smoking tobacco cigarettes than those who didn’t use e-cigs at all, and twice as likely to try smoking as those who used non-flavored e-cigs.

The study, led by Hongying Dai, Ph.D., a health researcher at Children's Mercy Hospital in Kansas City, Missouri, revealed another worrying finding: The students who used flavored e-cigs perceived both e-cigs and regular cigarettes as less harmful than those who didn't vape or who only used unflavored e-cigs.

Gregory Conley, president of e-cigarette advocacy group the American Vaping Association, says, “Teens are going to experiment. And, yes, some students who try e-cigs will end up being smokers." Conley adds that using e-cigarettes is a safer option than using tobacco cigarettes.

But Consumer Reports chief medical adviser Marvin M. Lipman, M.D. says there is reason for concern. “Smoking-associated diseases are a leading cause of death, and these studies suggest that flavored e-cigs—and their popularity with young people—could undo years of work educating people about the harms of tobacco products."

Mountain Dew, Cotton Candy, Wild Berry, and More

According to the Centers for Disease Control and Prevention, the number of U.S. adolescents using e-cigs has skyrocketed from an estimated 780,000 in 2013 to more than 3 million in 2015. Evidence that vaping may offer a fruit-flavored pathway to a traditional smoking habit makes that trend all the more troubling. 

“The enormous range of flavors lures kids into using these products,” Dai says. Later, her study shows, they may be more inclined to move onto to traditional cigarettes.

“When kids first try tobacco, they actually don’t like the bitterness,” Dai says. Flavored e-cigs remove that natural barrier between kids and a nicotine fix—“and because the kids are curious, they want to try all of these different flavors.”

Unlike regular cigarettes, e-cigs also come in a range of nicotine levels. But even low-nicotine e-cigs can contain enough of the addictive chemical to get teens hooked.

“Kids’ brains are uniquely sensitive to nicotine and they can become addicted more easily,” says Douglas Kamerow, M.D., M.P.H., a former assistant surgeon general and a professor of family medicine at Georgetown University.

Once they are addicted to nicotine, Dai says, teens may eventually try other products like cigars, hookahs, and cigarettes.

The bottom line is that we don’t want kids smoking or vaping, Lipman says: "That's one reason sweet-flavored cigarettes are already not allowed."

“Tobacco cigarettes are banned from containing flavorings—other than menthol—because they appeal to kids," Lipman explains. "Studies like this provide even more evidence that the Food and Drug Administration should ban them from e-cigarette liquid, too."