In a comprehensive analysis of existing studies, the U.S. National Academies of Sciences, Engineering, and Medicine concluded that electronic cigarettes are addictive, though less toxic than conventional cigarettes. The report also identified key areas for future research, including smoking cessation, adolescent use, and long-term health effects.

In a comprehensive analysis of existing evidence, the U.S. National Academies of Sciences, Engineering, and Medicine (NASEM) was unable to draw any definitive new conclusions about the use of electronic cigarettes (e-cigarettes), and instead identified a number of research gaps.

The NASEM committee reviewed more than 800 studies—funded by both industry and government—making their conclusions based on the quality of the available studies.

The committee found substantial evidence that e-cigarettes, which vaporize a nicotine-containing liquid that is then inhaled, expose users to fewer toxins than conventional cigarettes, and strong evidence of reduced harm for smokers who switch completely to e-cigarettes. It also found substantial evidence that e-cigarettes can be addictive, but little evidence on long-term health effects related to cardiovascular or respiratory diseases or cancers. However, the authors said there is substantial evidence that some chemicals present in e-cigarette aerosols can damage DNA and cause mutations.

A study published after the report was released offers additional evidence: Mice exposed to e-cigarette smoke had higher levels of DNA damage in their heart, lungs, and bladder, and human lung and bladder cells exposed to nicotine had more DNA damage, along with higher mutation rates and tumorigenic transformation.

Adolescents and young adults who use e-cigarettes are more likely to try conventional cigarettes, with moderate evidence that doing so will likely lead to smoking conventional cigarettes with greater frequency, the report said. However, all of the studies had short follow-up periods.

Whether e-cigarettes deliver on the claim that they can help smokers of conventional cigarettes to quit is less clear. The committee found limited evidence on the topic, and insufficient evidence to draw conclusions on how e-cigarettes compare to FDA-approved smoking cessation tools, such as nicotine gum and patches.

“The bottom line is there just aren't enough data to make firm conclusions, but that's the overall goal; we really have a public health responsibility to study [e-cigarettes],” says Jennifer Grandis, MD, of the University of California, San Francisco, who was not involved in the NASEM's work. “So, I think the big, screaming message of this report is, ‘Let's collect data in a scientific, rigorous way.’”

Whether a link exists between e-cigarette use and cancer is one of several gaps in knowledge. “I think that everybody has the instinct that it probably is related to cancer, but the question is dose and kinetics, and the problem is the latency of cancer formation,” Grandis says. “We need to develop metrics of exposure, and we need to collect the data and then we need to follow people for decades.”

According to Roy Herbst, MD, PhD, of the Yale School of Medicine in New Haven, CT, and chairman of the American Association for Cancer Research Tobacco and Cancer Subcommittee, more research is needed on nicotine, which he calls “pretty much the most addictive substance known to man.” For example, “Are there levels of nicotine that can be used that would be less addictive?”

One concern for Herbst: adolescent use of e-cigarettes, which aren't difficult to obtain and are often flavored to taste like bubblegum and cotton candy. “The use is so prevalent in high schools right now that I can't imagine that it's not getting people addicted to nicotine,” he says, noting that several large, long-term studies are under way.

Based on current evidence, Herbst does not recommend e-cigarettes to his patients as a smoking cessation tool, but he thinks the topic merits additional research. For example, he says that studies should assess whether e-cigarettes help people who have tried other smoking cessation methods without success. “But, they need to be clinical studies as there have been with the other forms of nicotine replacement.” –Catherine Caruso