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The jury is still out on whether electronic cigarettes will prove to have a net positive or negative impact on public health, according to a report from the National Academies of Sciences, Engineering, and Medicine.

The of existing e-cigarette studies to date, mandated by Congress, highlights areas of concern regarding e-cigarettes, such as the mounting evidence that non-smoking teens and young adults who vape are more likely to start smoking cigarettes.

But the expert analysis of more than 800 e-cigarette studies concludes that it is not yet possible to categorize e-cigarettes. "E-cigarettes cannot be simply categorized as either beneficial or harmful," writing committee chair David Eaton, PhD, of the University of Washington in Seattle, said in a statement.

Given the relatively short time that e-cigarettes have been on the market, their long-term health impact remains unknown, said committee member Maciej Goniewicz, PhD, PharmD, of Roswell Park Comprehensive Cancer Center in Buffalo, New York.

But, he told 名媛直播 that the report identified several key areas where the evidence is strong regarding e-cigarettes and public health.

"Electronic cigarettes are not safe, but there is conclusive evidence that they are less risky than smoking combustible cigarettes," Goniewicz said. "The evidence is very clear on this."

The report also highlights the preponderance of recent studies linking use of electronic cigarettes among adolescents and young adults to initiation of combustible cigarettes.

"Young people who use e-cigarettes have a higher risk of smoking," he said. "The good news is that, right now, this is not being reflected in a reversal of the downward smoking trend among teens."

Goniewicz said the studies examining the usefulness of e-cigarettes as smoking cessation tools among adult smokers have been limited, with the few randomized trials conducted to date showing little impact. Observational studies, in contrast, have shown a signal of benefit, he said.

"Our conclusion is that e-cigarettes may help smokers quit," he said. "But we need better randomized trials. This was one of our urgent recommendations."

Other conclusions in the report:

• There is conclusive evidence that exposure to nicotine from e-cigarettes is "highly variable and depends on the characteristics of the device and the e-liquid, as well as how the device is operated."
• There is substantial evidence that e-cigarette use results in symptoms of dependence on e-cigarettes.
• There is moderate evidence that risk and severity of dependence is lower for e-cigarettes than for conventional cigarettes.
• There is moderate evidence that variability in the characteristics of different components of e-cigarettes (nicotine concentration, flavoring, device type, and brand) are important determinants of the risk and severity of dependence on e-cigarettes.
• There is conclusive evidence that replacing combustible cigarettes with e-cigarettes reduces exposure to many toxicants and carcinogens.

With regard to second-hand smoke exposure, the writing group found moderate evidence that second-hand exposure to nicotine and particulate toxins is lower from e-cigarettes than from combustible cigarettes.

The writing group found "no available evidence" to weigh in on whether or not e-cigarette use is associated with an increased risk of cancer precursors in humans, such as polyps, but there was limited evidence from animal studies using intermediate biomarkers of cancer suggesting that long-term e-cigarette use could increase cancer risk.

The group noted that there is, as yet, no available evidence examining whether e-cigarette use affects fetal development or pregnancy outcomes or whether they cause respiratory disease.

Campaign for Tobacco-Free Kids President Matthew Myers called the many unanswered questions about the impact of e-cigarettes on public health "deeply troubling."

"This report shows what happens when a new product is introduced without meaningful government oversight," Myers noted in a press release. "It demonstrates why the FDA should fully and aggressively implement the overdue e-cigarette regulations that took effect in August 2016."

Myers called on FDA officials to reverse the decision to delay until August of 2022 key provisions of the 2016 deeming rule affecting e-cigarettes already on the market, which would require them to undergo scientific review by the agency.

He also called on the FDA to enforce requirements that new or modified products being introduced to the market undergo FDA review prior to their introduction, and to make manufacturers provide detailed information about what is in the products.

"Unless the FDA takes these steps, products that clearly appeal to kids -- including many sold in candy flavors like gummy bear and cotton candy -- will remain on the market for years to come and new ones will be introduced. In addition, smokers who want to quit will have no idea which, if any, e-cigarettes have been shown to be helpful, and manufacturers will have no incentive to invest in developing products that will actually help smokers quit," he stated.

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