A new study suggesting vapes may weaken the lung cancer benefits of quitting smoking was challenged during peer review over serious methodological concerns.
The study, published in Nature Medicine on June 8, analysed health data from more than 4.5 million adults in South Korea with a history of smoking.
It reported that former smokers who used vapes after quitting had higher risks of lung cancer incidence and lung cancer-specific death than former smokers who did not vape.
But one of the paper’s own peer reviewers repeatedly warned that the findings could be an artefact of the way the study was designed.
The reviewer said the authors’ interpretation “seems somewhat tendentious” and warned there was “a high probability” that the results reflected several methodological problems rather than a true vaping effect.
What the study claimed
The Nature Medicine paper, titled ‘Electronic cigarette use after smoking cessation and lung cancer risk’, used data from the Korean National Health Screening Program.
Researchers classified participants as current smokers, short-term quitters or long-term quitters, then compared lung cancer outcomes among those who did and did not report daily vape use.
The study found that, compared with former smokers who did not vape, former smokers who used vapes after quitting had a higher risk of lung cancer incidence and lung cancer-specific death.
The authors acknowledged that “causality cannot be established”, but said the findings suggest vape use after quitting smoking “may attenuate the benefits” of stopping smoking for lung cancer prevention.
That finding has already been turned into alarming headlines. The Daily Mail reported: “Swapping cigarettes for vapes does NOT significantly reduce the risk of lung cancer, study finds.”
Peer reviewer raised major doubts
The published peer review file shows that at least one reviewer raised repeated concerns about the central conclusion.
The reviewer said the cancers observed were likely to be the result of decades of smoking, rather than vaping.
They wrote: “The cancers that were observed were likely the result of decades of smoking and the finding, if genuine, would more likely suggest that vaping was reducing the benefits of stopping smoking.”
The reviewer’s main concern was that former smokers who vaped were likely to have quit smoking much more recently than former smokers who did not vape.
That is crucial because lung cancer risk falls over time after quitting. Someone who stopped smoking decades ago would be expected to have a lower lung cancer risk than someone who only stopped recently, regardless of whether they vaped.
The reviewer said: “The results may be just showing that risk reduction is proportional to duration of abstinence and have nothing to do with vaping.”
They also raised the possibility of reverse causality. In plain English, smokers who were already developing early symptoms of lung cancer may have been more likely to stop smoking and switch to vaping, making vaping look associated with cancer when the disease process had already begun.
The reviewer wrote: “Smokers with prodromal symptoms of lung cancer could have been more motivated to switch to vaping.”
Small numbers behind big claims
The study’s overall sample was huge, but the number of lung cancer cases among former smokers who vaped was much smaller.
Christopher Snowdon, writing in The Snowdon Substack, noted that there were 35,887 lung cancer cases in the study. Roughly half were among former smokers, but only 71 involved former smokers who used vapes.
Snowdon argued this made the finding much less solid than the headline sample size suggested.
The peer review file also shows concern about small event numbers in some subgroups. One reviewer said some analyses relied on “only 17 and 2” lung cancer-specific deaths among short-term and long-term quitters who used vapes.
Another said some results were based on tiny event counts and asked: “How can you draw any statistical conclusion from 2 events?”
Vapes and heated tobacco may have been mixed together
The most serious concern may be product misclassification. In a later review round, the critical reviewer said: “Alarmingly, I now also noted that the Korean NHIS questionnaire does not differentiate between heated tobacco products (HTP) and EC.”
That means some participants recorded as vape users may have been using heated tobacco products instead.
This is not a small technicality. Vapes heat a liquid to create an aerosol. Heated tobacco products heat processed tobacco. Treating them as the same exposure could distort conclusions about vaping.
The reviewer said the “key issues remain” after revisions and added that doubts remained over whether the conclusions “reliably reflect the data”.
Earlier scare stories have collapsed
The latest study comes shortly after another anti-vaping paper was retracted.
Snowdon’s article notes that a previous study claiming vaping causes COPD and asthma has now been withdrawn, and that one of its authors had another paper retracted last year after claims about vaping and stroke risk.
