- Youth vaping was projected to have only a very small effect on the chances of dying early over a lifetime.
- Even in the most pessimistic scenario, the average impact was equivalent to about 31 days of life lost.
- People who smoked at age 20 had a much higher projected risk of premature death, at around seven to eight per cent, compared with 0.15 to 0.84 per cent for those who vaped but had never smoked.
- Some scenarios showed a small increase in deaths linked to vaping, while others showed a small decrease. The researchers said the overall impact was “very small”.
Youth vaping is likely to have only a very small effect on the risk of dying prematurely over a lifetime, according to new research that modelled the long-term consequences for more than four million young Americans.
The study, published in the American Journal of Preventive Medicine, found that the availability of vapes could either slightly increase or slightly decrease lifetime mortality, depending on assumptions about their risks, how quickly people stop vaping and whether vaping helps smokers quit.
Across the scenarios tested, the difference was small. At the most pessimistic end of the main analysis, vaping increased the average person’s lifetime probability of premature death by 0.44 percentage points, equivalent to losing up to 31.3 days of life expectancy.
At the other end, it reduced the probability by 0.06 percentage points and increased life expectancy by up to 2.7 days.
The researchers said: “By far, the most important finding was that, positive or negative, the premature mortality impact is very small.”
Smoking carried far greater projected risk
The researchers followed a simulated cohort of 4.14 million Americans who were aged 12 in 2016, when youth vaping was becoming widespread.
They compared what was projected to happen over their lifetimes in a world where both cigarettes and vapes were available with a hypothetical scenario in which vapes had never existed.
The model took account of three possible effects. Vaping could lead some teenagers who otherwise would not have smoked to become smokers. Young people could continue vaping into adulthood without smoking. Vaping could also help some people who smoke to quit cigarettes.
In two illustrative sets of assumptions, somebody who was smoking at the age of 20 had a projected lifetime probability of premature mortality of around 7 to 8 per cent.
For somebody who vaped but had never smoked, the equivalent figure ranged from 0.15 to 0.84 per cent.
The researchers tested vaping mortality risks ranging from 5 to 30 per cent of the risk from smoking, alongside different assumptions about quitting.
They also carried out a sensitivity analysis assuming vaping carried 50 per cent of the mortality risk of smoking, a level the experts consulted for the study considered implausibly high. The number of projected life-days lost increased, but the overall conclusion remained broadly unchanged.
Most scenarios showed less than a week of life lost
Most of the combinations tested suggested vaping would produce some increase in lifetime mortality rather than a decrease.
But in most of those scenarios, the average reduction in life expectancy across the whole cohort was less than one week.
The results were particularly sensitive to how quickly people stopped vaping. When vaping cessation was assumed to be the same as smoking cessation, all the scenarios produced an increase in premature mortality.
When people were assumed to stop vaping more quickly than they stopped smoking, some scenarios produced a net fall in premature deaths.
Greater smoking cessation attributed to vaping also pushed the results towards lower mortality.
In one illustrative scenario, where vaping carried 15 per cent of smoking’s mortality risk, increased smoking cessation by 20 per cent and was stopped at three times the rate of smoking, the model projected 392 fewer premature deaths across the 4.1 million-person cohort.
Under a less favourable set of assumptions, with vaping carrying 30 per cent of smoking’s mortality risk and producing a smaller increase in smoking cessation, the model projected 4,222 additional premature deaths, equal to around 0.1 per cent of the cohort.
Researchers modelled the ‘gateway effect’
One of the central concerns around youth vaping is the possibility that it could encourage teenagers who would otherwise never smoke to start using cigarettes.
The model incorporated evidence linking adolescent vaping with later continued smoking.
But the researchers said it was impossible to determine how much of that association represented a genuine “gateway effect” caused by vaping and how much reflected “common liability”, where teenagers already more inclined to take risks are more likely to try both products.
The study also could not quantify the opposite possibility that vaping diverts some teenagers away from cigarettes.
The authors wrote: “No one knows the net effect of vaping on subsequent smoking.”
They pointed out that youth smoking fell particularly rapidly during the period in which youth vaping reached its highest levels.
Study deliberately used conservative assumptions
The researchers said several assumptions in the model were deliberately weighted towards producing greater mortality from vaping.
These included potentially underestimating how many teenagers would have become smokers if vapes had never existed, assuming teenagers who continued smoking for two years would still be smoking at 20, and treating all adult vaping as frequent enough to carry the full assumed health risk.
The study didn’t attempt to estimate illnesses that might be caused by vaping without resulting in death, while the health consequences of vaping initiated after the age of 20 were also excluded.
The researchers stressed that the true long-term health effects of vaping cannot yet be established through epidemiological evidence because the products have not been widely used for long enough.
But their modelling suggests mortality attributable to youth vaping is likely to remain small compared with the risks associated with cigarette smoking.
The paper concludes: “The key takeaway from this study is that, under a wide range of assumptions, projected mortality effects of adolescent
vaping-positive or negative-are very small.”
It adds that, “whatever its other effects, youth vaping is highly unlikely to constitute an important source of lifetime premature mortality.”
The study was funded by the US National Cancer Institute and Food and Drug Administration. The authors declared no conflicts of interest.
