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An umbrella review published in Tobacco Control looks at teen vaping and the risk of smoking and other health outcomes.
Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:
“This review paper is useful in that it takes a broad overall review of previous research on possible associations between vaping and various harms in young people. And generally it has been done competently, in my opinion. But that doesn’t mean its findings are easy to interpret. I’d say that, to a considerable extent, the new review tells us as much about what we still don’t know as about what we do know.
“The research is what’s called an umbrella review. That is, it’s a review of previous systematic reviews of studies in this area. That means that the findings are inevitable at a broad level, quite far away from the original studies that were reviewed in the original reviews on which it’s based. So really, it can’t present more than a quite generalised overall picture.
“And the quality of the findings in the new study depend on the quality of the systematic reviews on which it’s based, which depend in turn on the quality of the separate research studies that were used to produce those systematic reviews. As is good practice, the researchers who produced the new umbrella review assessed the 56 systematic reviews on which it’s based for their quality, and they rated only one of them as being of high quality and two as being of medium quality. The remaining 53 were considered to be of low or critically low quality. That’s not the fault of the authors of the new research, but it is an indication that we perhaps shouldn’t read too much into it.
“A major issue, and one that the researchers on this study acknowledge, is that it’s pretty well impossible to conclude that the associations between vaping and various health and behavioural outcomes are causal. That is, we don’t know whether those outcomes are actually caused by the vaping.
“That’s because the original studies, which fed into the systematic reviews that are reviewed in the new work, are observational. Observational studies always, on their own, lead to difficulties about cause and effect. In this case, there will be other differences between the young people who vape, and the young people who do not, apart from whether they vape. And those other differences could be the cause of bad outcomes that are correlated with vaping, and not the vaping itself. If a systematic review is based on observational studies, it’s hard to know much that’s definite about cause and effect from it. And if an umbrella review, like this one, is based on systematic reviews that can’t establish what’s causing what, then it can’t establish cause and effect either.
“The researchers on the umbrella review argue that their findings are consistent across different outcomes, and that that is consistent with the effects being causal. Well, it’s true that, if indeed vaping causes harms, this would be expected to show up consistently.
“But there are other possibilities. Young people’s behaviour generally changes in many ways during adolescence. Some young people might well carry out increasing amounts of behaviours that their parents and other people in positions of authority would disapprove of. This tendency to take risks, or to do things that might be risky, differs between individuals for all kinds of reasons – for instance, the young people’s own personalities and attitudes, and their relationships with their parents, teachers and friends. So some people might take actions apart from vaping, that cause future tobacco smoking, or health harms, because they generally tend take risks, and independently of that, they may also be more likely to vape because they see that as an attractively risky behaviour too. This would produce statistical associations between vaping and the smoking or health harms, that is not actually caused by vaping itself. And those associations might well be consistent.
“I’m not claiming that this explanation about risky behaviour is what’s going on, only that it’s another possibility that fits with the new study’s findings (or at least some of them).
“The press releases are rightly, very careful not to use language of cause and effect in discussing the findings of this study. The wording in the research paper is not always so careful: for instance its authors write, “The consistency in the evidence we present is striking; e-cigarette use raises the likelihood of future cigarette smoking among youth and young adults.” That sounds like a statement of cause and effect to me. But they also report that some of the authors of the systematic reviews that they summarised “questioned whether [the association between vaping and increased risk of starting to smoke] was a causal effect.”
“In some cases, the authors of the systematic reviews behind this umbrella review, and/or the authors of the original studies that they reviewed, would have made statistical adjustments, or other arguments, to explain why they feel that an association they found was indeed causal. That would never take away entirely the problem of not knowing about cause and effect, but it can help. However a problem with an umbrella review, like this one, is that such detail does tend to get lost in taking such a high-level overview.”
Dr Emma Beard, Associate Professor in Statistics and Quantitative Methods, University College London, said:
“The University of York’s press release presents an overly strong conclusion that is not fully supported by the data detailed in the full paper. While the review finds a consistent association, the press release downplays the authors’ own significant caveats about inferring a direct causal link, particularly since a staggering 70% of the systematic reviews included were judged to be of ‘critically low’ quality. The paper also rightly acknowledges that the link could be explained by the ‘common liability hypothesis’, which is the idea that some individuals are simply predisposed to risk-taking behaviours. The conclusion that vaping acts as a ‘gateway’ is an overspeculation, especially when the paper notes that at a population level, smoking rates have generally fallen as vaping has risen. While protecting youth is vital, this review clearly shows the current evidence base on this topic has some significant weaknesses.”
Dr Richard Holliday, Senior Lecturer and Honorary Consultant in Restorative Dentistry, Newcastle University, said:
“This review identifies a number of studies that have evaluated health outcomes in young people who vape – notably, oral health risks. There are major issues with confounding effects from tobacco smoking in the e-cigarette/oral health research field i.e. e-cigarette users are also often smoking, making it hard to identify the effect of e-cigarettes alone (a recent systematic review and meta-analysis explored this [1]). Although this review briefly mentioned confounding effects in the discussion it was not part of their analysis – this undermines their conclusion that there are ‘significant associations’ between vaping and oral health harms.”
“There are mixed messages with regards to the oral health risks in this paper. The abstract states there are ‘significant associations’ between e-cigarette use an oral health harms. However, in the conclusions they say oral health harms are ‘possibly associated’ with e-cigarette use. I agree with the conclusion that further research is needed in this field.”
1 – https://www.nature.com/articles/s41432-025-01119-6
Prof Ann McNeill, Professor of Tobacco Addiction, King College London, said:
“This umbrella review brings together in one place issues relating to young people, e-cigarettes and health effects. It reported on 56 systematic reviews of which 53 were rated critically low or low quality, meaning authors should be extremely cautious before making any conclusions.
“The authors reported that the reviews found consistently that vaping was associated with subsequent smoking. This replicates the findings of many previous reviews and indeed research I have been involved in. However, the authors incorrectly state that this supports ‘a causal relationship’ in other words that vaping causes smoking (the so-called ‘gateway’ effect). It is well-established that consistency does not mean causality. In this case, individual-level studies that were the focus of these reviews do not take into account all the possible influences on these behaviours, such as being sensation-seeking or impulsive which might make young people more likely to vape and to smoke. Our research also showed the opposite relationship – that trying a tobacco cigarette was associated with subsequent vaping. Indeed, a recent well conducted systematic review published using gold standard methods, reported a similar finding to the umbrella review for individual-level studies – but it found the opposite in studies examining population-level trends in vaping and smoking, so as youth vaping increased in a population, smoking reduced. Given these authors also talked about limited evidence, we need more and better research to be able to make confident conclusions about the relationship between youth e-cigarette use and health outcomes.
“The umbrella review’s finding of a relationship between vaping and subsequent substance use suffers from similar issues. Furthermore, findings on other health outcomes were often examined in cross-sectional studies, which take a snapshot of people at one point in time. These simply show a relationship, such as that between vaping and mental health but cannot say anything about what came first, and hence whether vaping caused the mental health condition or whether the mental health condition caused young people to vape.
“Nevertheless, we are all keen to protect young people’s health and concerns about youth smoking and vaping have prompted the government to introduce its Tobacco & Vapes Bill and its passage through Parliament should be accelerated.”
Prof Peter Hajek, Professor of Clinical Psychology, and Director of the Health and Lifestyle Research Unit, Queen Mary University of London (QMUL), said:
“Some of these associations have well known explanations. People with mental health issues are more likely to be attracted to psychoactive substances, and the same people who try one are also likely to try others. The link of vaping to asthma is more concerning but it requires further corroboration. The relevant studies included adults with smoking history, not never-smoking youth, and were previously criticised because the link could have been due to smoking rather than vaping, especially as smokers were included who had asthma before switching to vaping.”
Dr Stephen Burgess, Statistician, University of Cambridge, said:
“This research is a compilation of observational studies, each of which compares vaping users against non-users. As such, it can say that vaping users are more likely to engage in certain behaviours, but whether vaping is truly a cause of these behaviours is beyond the scope of the data. However, the associations demonstrated are both extensive in scope and strong in magnitude – it is clear that vaping users are at higher risk of many diseases than non-users. A causal explanation to the findings is both plausible and consistent with the evidence provided but such a finding can only be made conclusively by a randomized trial. Given that a large-scale long-term trial would be impractical and potentially unethical, it is likely that we will never have conclusive evidence demonstrating that vaping behaviour is a cause of health outcomes. Vaping users need to make decisions about their behaviour based on evidence that is inherently uncertain, but links vaping usage with a host of negative outcomes”
‘Vaping and harm in young people: umbrella review’ by Golder et al. was published in Tobacco Control at 23:30 UK Time Tuesday 19th August 2025.
DOI: 10.1136/tc-2024-059219
Declared interests
Prof Peter Hajek: None
Prof Ann McNeill: None
Dr Stephen Burgess: None
Dr Richard Holliday: None
Dr Emma Beard: “I have received unrestricted research funding from Pfizer in the past”
Prof Kevin McConway: None