Young people who use e-cigarettes are significantly more likely to try conventional cigarettes later on, a new study suggests.

Whether e-cigarettes serve as a “gateway” to traditional tobacco products is hotly debated. But the new study, published in JAMA Pediatrics, finds that young people who use e-cigarettes are much more likely to start using conventional cigarettes within a year compared to peers who do not use e-cigarettes.

Researchers at the University of Pittsburgh Center for Research on Media, Technology, and Health (CRMTH) and the Dartmouth-Hitchcock Norris Cotton Cancer Center looked at about 700 people from ages 16 to 26 who did not smoke cigarettes. At the study’s start, the men and women were asked if they would try a cigarette if a friend offered them one, or if they thought they would smoke a cigarette within the next year. Those who answered “definitely no” were found to be “non-susceptible” to cigarette smoking. The group was surveyed in 2012 and again in 2013.

MORE: Teen E-Cig Smokers Are More Likely To Turn To Cigarettes: Study

During that year, things changed—especially for those who used e-cigarettes. When the young men and women were surveyed again, more people who said they used e-cigarettes at the start of the study had started using regular cigarettes, compared to people who did not use e-cigarettes.

Notably, the number of young people who used e-cigarettes at the start of the study was small. Out of the 694 people in the study, only 16 were e-cigarette users at the start. Six of those 16 people, or 37.5%, used cigarettes a year later. Just 65 out of the 678 people who did not use e-cigarettes progressed to smoking cigarettes, or 9.6%.

The authors say that because the number of e-cigarette users at the start of the study was so small, it could be inferred by others that the public health risk with smoking e-cigarettes may not be “substantial”. But other data, they note, suggest that increasingly more young people are starting to use e-cigarettes, and as many as half of them do not use traditional cigarettes. Any overlap in use should be monitored, they say.

MORE: The Best Way To Quit Smoking Isn’t E-Cigs

One of the public health issues surrounding e-cigarettes is the fact that the U.S. Food and Drug Administration (FDA) currently does not regulate e-cigarettes as it does other tobacco products, though it proposed an expansion of its jurisdiction to do so in 2014. E-cigarettes are still subject to regulation by other entities like states or counties or cities. As the study authors note in their report, this still means that in some cases e-cigarettes are not subject to restrictions like age limits. The study authors also add that e-cigarettes come in flavors like bubble gum and chocolate which could be attractive to younger consumers.

E-cigarettes are still not fully studied, the FDA says. “It is not known whether e-cigarettes may lead young people to try other tobacco products, including conventional cigarettes, which are known to cause disease and lead to premature death,” the group says on its website. However, study author Dr. Brian A. Primack, director of CRMTH, disagrees with the notion that there’s not enough information to determine the public health risk of e-cigarettes. “I do think that things have changed,” he says in an email to TIME. “This study, in combination with other recent findings, raises more concerns about some potential harms to the public health.”

The researchers conclude that their findings support regulation that limits e-cigarette sales and lowers their appeal to young adults. The FDA plans to restrict sales, though the proposed rules by the FDA are not yet enforced.

Get our Health Newsletter. Sign up to receive the latest health and science news, plus answers to wellness questions and expert tips. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Contact us at letters@time.com.