SEOUL — The largest study yet on what happens to lungs after smokers switch to vaping has delivered a blunt verdict: quitting nicotine entirely, not substituting one delivery system for another, is the only clear path to lower cancer risk. Researchers at Seoul National University Bundang Hospital tracked over 4.5 million Korean adults with a history of smoking combustible cigarettes. The data, drawn from the National Health Screening Program and published in Nature Medicine, covered more than 24 million person-years of follow-up through December 2023.
During that period, 35,887 new lung cancer cases and 12,807 lung cancer-related deaths were recorded. The study grouped former smokers into three categories: those who quit both cigarettes and e-cigarettes completely, those who switched to daily e-cigarette use, and those who continued smoking traditional cigarettes.
The healthiest outcomes were consistently seen among complete quitters. Former smokers who used e-cigarettes daily faced an adjusted hazard ratio of 1.56 for lung cancer and 2.00 for lung cancer-specific death compared with those who quit nicotine entirely. For context, people who continued smoking combustible cigarettes had a 1.78 times greater risk of lung cancer.
The pattern suggests that while vaping may be less harmful than continued smoking, it is not a harmless alternative. The 56 per cent higher lung cancer risk among vapers compared to complete quitters is a figure that lung cancer specialists say should reshape public health messaging.
For years, e-cigarettes have been marketed as a less harmful option, with many smokers turning to vaping in the hope of protecting their lungs. The South Korean study directly challenges that narrative. “This is the scale of evidence we’ve been waiting for,” said a pulmonologist at a major Seoul teaching hospital who was not involved in the study.
“The cohort is massive. The follow-up is long. The message is clear: switching to vaping is not the same as quitting.” The study’s authors at Seoul National University Bundang Hospital noted that the data came from a nationwide cohort, making it one of the largest investigations into the long-term health effects of vaping after smoking cessation.
The adjusted hazard ratios accounted for age, sex, income, alcohol use, exercise, and body mass index. Critically, the risk for vapers fell between complete quitters and continuing smokers.
That gradient matters. It means vaping is not as bad as smoking, but it is far from safe. The 56 per cent increased risk for lung cancer and the doubling of lung cancer-specific death risk among vapers are numbers that specialists say should give pause to anyone promoting e-cigarettes as a cessation tool.
“The idea that vaping is a harmless alternative has been a convenient fiction,” the pulmonologist said. “This study shows it’s a fiction with real consequences.” The research also raises questions about the long-term trajectory of lung cancer risk among vapers.
With follow-up extending only through 2023, some specialists worry that the true toll may be higher as more time passes. Lung cancer often takes decades to develop, and the study’s participants had a history of smoking combustible cigarettes before switching. “We may be seeing only the beginning of the damage,” the pulmonologist added.
“The lungs don’t forget past exposure, and they don’t forgive new exposure.” For public health officials, the findings present a dilemma. E-cigarettes have been widely promoted as a harm reduction tool for smokers who cannot or will not quit nicotine entirely. The study does not dispute that vaping is less harmful than continued smoking.
But it does argue that the gap between vaping and complete cessation is wide enough to demand a re-evaluation of policy. The study’s authors did not call for a ban on e-cigarettes.
They did not offer policy recommendations. They simply presented the data. The numbers speak for themselves: 56 per cent higher lung cancer risk.
Double the lung cancer death risk. And zero benefit compared to quitting altogether.
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