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Do e-cigarettes help smokers kick their bad habits, or do they end up promoting tobacco use among young people? It’s one of the most intensely debated questions in drug abuse research, but the current answer is unsatisfying: We need more evidence to clearly say who’s right.

E-cigarettes — the electronic devices that allow people to “smoke” nicotine-laced vapor instead of combustible, tobacco-based products — have been the subject of polarized science ever since they gained popularity in 2006. For proponents of the technology (also known as “vaping”), e-cigarettes represent a free-market solution to tobacco addiction, offering smokers an effective way to consume nicotine while giving up the nasty chemicals in tobacco products. This is not a fringe movement: In Britain, e-cigarettes are actively promoted by doctors as a substitute for smoking traditional cigarettes.

For critics, though, e-cigarettes are just a stepping stone to tobacco use. After achieving substantial headway in the reduction of smoking over the past few decades, many health advocates fear that the recent surge in vaping endangers the progress we’ve made, particularly among young people.

The debate reignited last week after the academic journal Tobacco Control published a study claiming that e-cigarettes serve as a “one-way bridge” among young people to smoking combustible cigarettes . The study, which comes out of the Institute for Social Research at the University of Michigan, reviews survey data from 347 high school students throughout the United States on their use of cigarettes in 2014 and again as a follow-up in 2015. The study found that those who had vaped in 2014 were more than four times as likely to have reported smoking tobacco products in the following year.

E-cigarette proponents quickly picked apart the study. Michael Siegel of Boston University, a tobacco control researcher, argued in a series of blog posts that the sample size was too small, noting that the conclusion rests on the smoking habits of just four students in the survey. Linda Bauld of the University of Stirling, who also studies tobacco control policies, reiterated an argument commonly featured in the e-cigarette debate: Even though vaping surged among young people over the past decade, tobacco usage rates continue to decline.

Richard Miech, author of the study and a professor at the University of Michigan, defended his work in a phone interview, arguing that the conclusion is based on statistically significant data that is nationally representative. He also noted that his study backs up a handful of other studies examining the same question.

“I feel like the science behind my study is sturdy,” Miech said, also noting that e-cigarette proponents have consistently challenged studies that come to the same conclusion. “Critics are going to keep denying [these studies] even as each new one comes out.”

Still, Miech readily concedes that research on the topic is still relatively young and that more data needs to be collected. It took decades of rigorous academic research before the scientific community generated consensus that tobacco use was a public-health crisis. Should we really expect to have clear answers on the effects of vaping within a 10-year period of the product surging onto the market?

Still, the National Institute on Drug Abuse already proclaims on its website that young people who vape are more likely to try tobacco products. Meanwhile, defenders of e-cigarettes religiously believe that the product helps addicts quit smoking, even though the most recent and thorough meta-analysis on the topic was inconclusive as to whether that was the case.

What is well-established, however, is that vaping isn’t a healthy habit. Health experts warn that nicotine ingested while vaping can hurt arteries and increase the risk of heart disease. Some brands also contain formaldehyde, which increases the risk of cancer, and a few flavorings added to e-cig vapor contain diacetyl, which has long been associated with a lung disease called “popcorn lung.” Just last week, researchers at Johns Hopkins also found high levels of toxic metals in e-cigarette vapor.

“When you smoke chemicals, it’s almost like taking an IV with those chemicals and putting them straight into your bloodstream,” Miech said.

As a substitute to the long list of harmful chemicals found in combustible cigarettes, these harmful substances might be a desirable trade-off. But even the most ardent supporters of e-cigarettes should admit that the surge in teen vaping is probably not a good thing, whether or not it leads to increased tobacco use.

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