SEOUL — A South Korean study tracking more than 4.5 million adults has produced stark numbers on vaping after quitting cigarettes. The data, published in Nature Medicine, shows former smokers who switched to daily e-cigarette use faced double the risk of dying from lung cancer compared to those who quit nicotine entirely. Researchers at Seoul National University Bundang Hospital analyzed health records from the Korean National Health Screening Program.
The cohort included 4,524,895 Korean adults with a history of smoking combustible cigarettes. Follow-up ran until December 2023, covering over 24.18 million person-years.
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. Complete quitters had the best outcomes by a wide margin.
Former smokers using e-cigarettes daily had an adjusted hazard ratio of 1.56 for lung cancer and 2.00 for lung cancer-specific death compared to complete quitters. That means a 56 percent higher risk of developing lung cancer and double the risk of dying from it.
For context, people who kept smoking combustible cigarettes had a 1.78 times greater risk of lung cancer — higher than the vaping group, but not by a wide margin. The pattern is clear. Vaping may be less harmful than continued smoking, but it is not a harmless alternative.
The healthiest path remains quitting nicotine altogether. What could go wrong next? The study’s size — one of the largest ever on this question — suggests the risks are not marginal.
If millions of former smokers have switched to daily vaping believing it protects their lungs, these numbers indicate many could develop cancer anyway. The risk of lung cancer death doubling is the kind of figure that should shift public health messaging.
South Korea’s National Health Screening Program already collects data on smoking and vaping habits. Researchers used that infrastructure to produce this study. The question is whether health authorities will act on it.
Warning labels on e-cigarettes in South Korea currently emphasize nicotine addiction, not cancer risk. That could change.
Other countries face the same problem. The United Kingdom’s National Health Service has promoted vaping as a smoking cessation tool. The United States allows e-cigarette sales while regulating nicotine levels.
These policies were built on the assumption that vaping is substantially safer than smoking. This study chips away at that assumption. The data also raises questions about how e-cigarettes cause harm.
Combustible cigarettes produce tar and thousands of chemicals from burning tobacco. E-cigarettes heat liquid nicotine, producing an aerosol with fewer toxicants.
But “fewer” is not “none.” The study did not examine biological mechanisms, but the numbers suggest chronic vaping carries its own carcinogenic risk. Researchers followed participants until December 2023. The study period captured long-term outcomes, but e-cigarette use has evolved.
Newer devices deliver higher nicotine concentrations and operate at higher temperatures. Whether those changes increase or decrease risk remains unknown.
For now, the message from Seoul is blunt. Quitting smoking by switching to vaping is not quitting. It is trading one risk for another.
Complete cessation — no cigarettes, no e-cigarettes — is the only strategy that eliminated the elevated risk in this study. Everything else carried a price.
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