Sifting through contradictory evidence is common when it comes to choosing the right thing to do to improve our health, not least at new year when many of us promise to leave old habits behind and make a fresh start. One topic that is almost guaranteed to provoke arguments is e-cigarettes. Thousands of research papers have been published about these devices over the past decade. But we do not seem to be much closer to a global consensus on their risks or benefits, and arguably the debate is becoming more entrenched. What is going on?

A number of factors appear to be fuelling this, but in 2018 one more than any other seemed to be driving the debate. It relates to the consequences of e-cigarette use by young people, and the extent that youth vaping will lead to smoking. In other words: are e-cigarettes creating a new generation of nicotine users, and will these vapers become the smokers of the future?

Scientists and regulators on both sides of the Atlantic pondered the evidence on these questions in 2018 and came to different conclusions. In the US, the National Academies of Science, Engineering and Medicine reported that “there is substantial evidence that e-cigarette use increases risk of ever using combustible tobacco cigarettes among youth and young adults”. Advice from the Centres for Disease Control and Prevention says: “E-cigarettes are not safe for youth, young adults, pregnant women or adults who do not currently use tobacco products.”

In the UK, an updated evidence review from Public Health England concluded: “E-cigarettes are attracting very few young people who have never smoked into regular use, and e-cigarettes do not appear to be undermining the long-term decline in cigarette smoking in the UK among young people.” In addition, a House of Commons science and technology committee report stated: “Concerns about the risk of e-cigarettes potentially providing a ‘gateway’ into conventional smoking have not materialised to any significant degree.”

What explains these differences?

Trends in vaping may be diverging between the UK and US – two countries that have traditionally taken a fairly permissive approach to e-cigarettes. Surveys in both countries include questions on experimentation with vaping, such as whether a person has ever tried an e-cigarette. This type of experimentation is more common in the US than the UK. Among teenagers in their final year of secondary school in the US, around age 18, 37% reported having tried an e-cigarette in the past year. Among 18-year-olds in Great Britain, the most recent survey data found 23% had tried vaping. In addition, two large national youth surveys in the US, Monitoring the Future and the National Youth Tobacco Survey, found significant increases in the use of e-cigarettes between 2017 and 2018, a sharp rise not seen in the UK.

Differences in how use is measured may play a role. In the US, survey questions focus on whether someone has ever used an e-cigarette or whether they have used one recently (in the past 30 days). Use in the past 30 days is a broad measure that means teenagers who may simply have tried an e-cigarette once or twice in the past month are included in those figures. In the UK, in contrast, there has been a focus on measuring regular use (at least weekly) and on whether young people who have never smoked cigarettes are vaping. UK figures over several recent years have found that regular use of e-cigarettes by teenagers who have never smoked remains very low, at less than 1%.

Differing policies may also help explain these differences. In the UK, almost all forms of e-cigarette marketing have been banned since 2016. This is not the case in the US. In addition, newer devices appear to be popular with young Americans. These include Juul, which are small, discreet, easy to use and deliver nicotine more rapidly than older models, and have only recently become available in the UK. The EU also imposes limits on the amount of nicotine in e-cigarettes, controls not in place in the US.

Facebook Twitter Pinterest Newer devices such as Juul have proven popular with young Americans. Photograph: Seth Wenig/AP

Attitudes to nicotine also differ. The UK has official guidance on tobacco harm reduction that recognises nicotine is not the harmful substance in tobacco (it is the thousands of other chemicals in cigarettes) and nicotine replacement therapy is licensed for use in smokers who are pregnant or children above the age of 12. In the US, the statement that nicotine harms the developing brain (evidence that comes from studies with mice and rats, not humans) is widely used in official documents. This means any e-cigarette use by American youth, even experimentation, is viewed as a cause for concern.

This transatlantic debate has wider implications because reports of study findings are played out in the global media, causing confusion in countries that have not yet decided how to regulate e-cigarettes. The reported rise in youth vaping in the US has resulted in a crackdown on the American e-cigarette market, with the US Food and Drug Administration (FDA) requiring Juul and other similar products to be removed from many retail outlets. The FDA has invested in graphic public information campaigns to discourage youth vaping. These campaigns emphasise the risks without mentioning the research that shows e-cigarettes can help smokers quit. One consequence is that only 2.6% of Americans now believe vaping is much less harmful than smoking, despite plenty of research showing that to be the case.

This misperception of the risk is seen in the UK as well, albeit not to the same degree. Research published on Friday in the journal Addiction found that even among smokers and ex-smokers in the UK, just over half surveyed (57.3%) correctly believed e-cigarettes were less harmful than smoking, while 25% believed them to be equally or more harmful. Many of those surveyed (nearly four in 10) incorrectly believed that nicotine was the cancer-causing compound in cigarettes, and almost nine in 10 overestimated the health risk from nicotine.

Evidence from the US and UK combined indicates that efforts to deter teenagers from trying vaping may discourage adult smokers from using e-cigarettes to quit smoking. Fortunately, in both countries smoking rates continue to decline for both adults and young people, a fact often forgotten amid the furore about e-cigarettes. If e-cigarettes were a gateway to tobacco, these trends would stall or be reversed. And in the UK at least, government agencies and leading charities actively support vaping as a positive choice for smokers trying to stop.

We should not be forced to choose between protecting children and supporting the one in two adult smokers who will suffer and die prematurely from a smoking-related disease if they continue to smoke. The challenge in 2019 and beyond will be to ensure the right balance is struck.

Prof Linda Bauld is professor of public health at the University of Edinburgh, deputy director of the UK Centre for Tobacco and Alcohol Studies, and holds the Cancer Research UK (CRUK)/Bupa chair in behavioural research for cancer prevention at CRUK.

Dr Suzi Gage is a lecturer at the University of Liverpool. She is funded by CRUK to investigate e-cigarette use in young people in the UK. She is on Twitter @soozaphone, and makes the award-winning Say Why to Drugs podcast.