"Children who tried e-cigarettes are 12 times more likely to start smoking tobacco," is the hard-hitting headline from the Mail Online. But the link is not as robust or clear-cut as this would have you believe.
The story is based on a survey of more than 1,000 young people from across the UK. They were asked about their use of cigarettes and e-cigarettes – commonly referred to as "vaping" – at the start of the study and again after 6 months.
While it's true that those who had never smoked but had tried e-cigarettes were 12 times more likely to have tried smoking at follow-up, this finding was based on just 21 people.
Therefore, the study doesn't provide firm evidence that using e-cigarettes will lead to smoking. What it does show, as would be expected, is that it's very rare for non-smokers to use e-cigarettes.
Although the health risks of e-cigarettes are still relatively unknown, recent Public Health England (PHE) research found they pose only a fraction of the risks of smoking. That said, e-cigarettes – or more specifically, the nicotine inside them – is highly addictive, so vaping can become an expensive habit with no real benefits.
The study was carried out by researchers from King's College London, the University of Nottingham, PHE, and Action on Smoking and Health UK. It was funded by Cancer Research UK and published in the peer-reviewed Journal of Adolescent Health.
The Mail Online referred to the evidence as "strong" and didn't note the study was essentially cross-sectional, covering only a 6-month period, which actually weakens the case.
This was a survey of 11- to 18-year-olds from the UK, with baseline data collected in April 2016, and follow-up data collected between August and October 2016. It investigated whether use of e-cigarettes was linked with later smoking.
Surveys look at a group of people at one point in time. When enough people are included, surveys are useful for estimating how common particular health problems are, but they can't discern anything about cause and effect (causation).
This research used data from the 2016 Action on Smoking and Health Great Britain Youth longitudinal survey, which used email to recruit a representative UK sample of people aged 11 to 18.
At baseline, people were grouped into those who had never smoked ("Not even one puff") or who had ever smoked, however briefly. At follow-up 4 to 6 months later, they were grouped into those who had:
The same groupings were used for e-cigarette use.
The researchers compared how smoking and e-cigarette use had changed between baseline and follow-up, adjusting for confounding factors. These included:
People who didn't know what e-cigarettes were, didn't want to disclose their habits or answered "Don't know" for their smoking status were excluded.
The final analysis included 1,152 people. At baseline, 80% had never smoked and 89% had never used e-cigarettes.
It was more common for young people to have smoked cigarettes than used e-cigarettes at baseline.
Among 923 people who'd never smoked at baseline, those who had tried e-cigarettes were 12 times more likely to have tried smoking by follow-up than people who had never used e-cigarettes (odds ratio [OR] 11.89, 95% confidence interval [CI] 3.56 to 39.71). However, this group comprised just 21 people.
Those who had ever used e-cigarettes and who increased their use were more likely to initiate smoking than those who didn't increase their e-cigarette use (OR 7.89, 95% CI 3.06 to 20.38). This was based on 41 people.
Among 1,020 people who'd never tried e-cigarettes at baseline, those who'd tried smoking were 3.5 times more likely to try e-cigarettes by follow-up than those who hadn't ever smoked (OR 3.54, 95% CI 1.68 to 7.45), based on 118 people who had ever smoked.
Finally, those who smoked and increased their smoking were more likely to initiate e-cigarette use than those who didn't increase their smoking (OR 5.79, 95% CI 2.55 to 13.15). This was based on 88 people who increased their smoking.
The researchers said the study provided evidence for "a prospective association between ever e-cigarette use and smoking initiation, and between ever smoking and e-cigarette initiation".
They added that a better understanding of these associations would aid policymakers in their efforts to develop an appropriate regulatory framework for tobacco products and e-cigarettes.
This research provides further insight into the relationship between smoking and e-cigarette use among young people. But the most important thing to realise is that, despite the media headlines, it does not provide firm evidence that people who try e-cigarettes without having smoked previously are then more likely to start smoking.
It's true that e-cigarettes users who'd never smoked were 12 times more likely to start smoking, but there were only 21 people in this category in the analysis. The wide confidence intervals around this risk figure indicate how uncertain an association it is.
The low number of people who had never smoked and who went on to use e-cigarettes is consistent with other smoking research in the UK. This suggests e-cigarettes are unattractive to people who have never smoked.
We still don't know exactly how many young people who have never previously smoked but choose to try e-cigarettes go on to become smokers, but we can say that using e-cigarettes is associated with smoking tobacco and vice versa.