The prestigious National Academies of Sciences, Engineering, and Medicine released a new report on e-cigarettes that’s the most comprehensive look at the evidence to date.

A panel of experts analyzed the findings of 800 peer-reviewed studies and came out with a grab bag of conclusions about e-cigarettes’ health impact — finding that while e-cigarettes are safer than conventional cigarettes for individual smokers, their public health consequences are still unknown.

In the NAS report, the authors repeatedly state that e-cigarettes are far less harmful than conventional cigarettes. “There is conclusive evidence,” the report says, “that completely substituting e-cigarettes for combustible tobacco cigarettes reduces users’ exposure to numerous toxicants and carcinogens present in combustible tobacco cigarettes.”

This paves the way for regulators and policymakers to move toward the kind of harm reduction approach other countries are already experimenting with — a direction the Food and Drug Administration, which recently gained the authority to regulate e-cigarettes, seems to be heading in.

1) E-cigarettes may — or may not — help adults quit smoking

A Juul e-cigarette in a Boston vaping shop on November 15, 2017. E-cigarettes are battery-powered devices that vaporize liquid nicotine. Suzanne Kreiter/The Boston Globe via Getty Images

E-cigarettes are generally slender, battery-powered devices that turn liquid nicotine into vapor, imitating conventional smoking. But the devices heat the liquid at a lower temperature than the burning regular cigarettes require — hence why the verb “vaping” is used instead of “smoking” for these products.

One of the most critical questions about e-cigarettes is whether they can help smokers quit traditional cigarettes. This was also one of the questions for which the NAS committee had the most limited evidence.

In the report, the reviewers were careful to draw their conclusions based on the strength of the available evidence. In their eyes, conclusions based on experimental studies — like randomized controlled trials — had more heft than conclusions based on observational research.

2) Vaping increases the likelihood that young people will smoke cigarettes

On the other hand, there is strong evidence that e-cigarettes may act as a gateway to traditional cigarettes among youth.

“The evidence base was large enough and consistent enough and strong enough to conclude that there’s an association between e-cigarette use and ever-use of combustible tobacco [cigarettes],”

Either way, this is a very important finding because another key question about the introduction of e-cigarettes to the market has been what impact they’ll have on youth smoking rates, which have dropped precipitously in recent years. And this NAS finding suggests vaping may have negative health consequences here.

The committee had 10 high-quality studies to base its conclusions on, and they all pointed to the same effect. “That’s why we decided to make this conclusion much stronger: Children using e-cigarettes are at an increased risk of using tobacco cigarettes in the future,” said committee member Maciej Goniewicz, an oncologist at Roswell Park Comprehensive Cancer Center.

So again, while e-cigarettes might have the benefit of helping adults quit smoking, they may also promote smoking among youth and young adults.

3) E-cigarettes are less harmful than conventional cigarettes

E-cigarette vaporizers are displayed at Digital Ciggz on January 28, 2015, in San Rafael, California. Justin Sullivan/Getty Images

On one fact, the report was clear: When compared to conventional cigarettes, e-cigarettes appear to be safer.

Before going into the details, let’s just be clear on the baseline: Conventional cigarettes are one of the deadliest products available to consumers. They are still responsible for nearly one in five deaths in the US.

“Overall, e-cigarette aerosol contains fewer numbers and lower levels of toxicants than smoke from combustible tobacco cigarettes,” the committee found. There is also “conclusive evidence that completely substituting e-cigarettes for combustible tobacco cigarettes reduces users’ exposure to numerous toxicants and carcinogens present in combustible tobacco cigarettes” and “substantial evidence that completely switching from regular use of combustible tobacco cigarettes to e-cigarettes results in reduced short-term adverse health outcomes in several organ systems.”.

For example, some e-cigarettes contain not only nicotine but other toxicants and carcinogens, like formaldehyde and acrolein. And there’s evidence that use of the devices can exacerbate asthma in adolescents who use them and increase coughing or wheezing.

What long-term effects this will have on adolescents’ lungs, we don’t know. We also don’t yet know what effect e-cigarettes have on pregnancy outcomes or long-term cancer risk and cardiovascular outcomes. And there’s the “conclusive evidence” that e-cigarettes can explode and burn people, and that the liquids in e-cigarettes can be fatally poisonous.

4) The big-picture health effects of e-cigarettes are still a question mark

To try to understand what effect e-cigarettes may have on public health in the future, the committee modeled several scenarios — and they all hinged on the effect e-cigarettes had on smokers quitting (see No. 1 on this list).

The fact that the evidence on this question was so limited made it pretty difficult to draw firm conclusions about whether e-cigarettes will be a helpful harm reduction tool at the population level.

But most of the simulations showed that e-cigarettes likely have a net public health benefit — at least in the short run — even if they lead some young people to take up smoking. Here’s the conclusion from the report:

Under the assumption that using e-cigarettes increases the net cessation rate of combustible tobacco cigarettes among adults, the modeling projects that in the short run, use of these products will generate a net public health benefit, despite the increased use of combustible tobacco products by young people. Yet in the long term (for instance, 50 years out), the public health benefit is substantially less and is even negative under some scenarios. If the products do not increase combustible tobacco cessation in adults, then with the range of assumptions the committee used, the model projects that there would be net public health harm in the short and long term.

Again, the public health question hinges on whether over time, the e-cigarette market can displace much of the tobacco market and get most smokers to make the switch.

What are e-cigarettes?

An electronic cigarette (or e-cig) is a battery-powered vaporizer that mimics tobacco smoking. It works by heating up a nicotine liquid, called “juice.”

Nicotine juice (or e-juice) comes in various flavors and nicotine levels. e-liquid is composed of five ingredients: vegetable glycerin (a material used in all types of food and personal care products, like toothpaste) and propylene glycol (a solvent most commonly used in fog machines.) propylene glycol is the ingredient that produces thicker clouds of vapor.

Proponents of e-cigs argue that the practice is healthier than traditional cigarettes because users are only inhaling water vapor and nicotine.

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