Former smokers who switched to daily e-cigarettes had a 56 per cent higher risk of lung cancer than those who gave up both habits. That is the headline figure from a South Korean study published in Nature Medicine.
Researchers at Seoul National University Bundang Hospital looked at the health records of 4,524,895 Korean adults who had smoked regular cigarettes. The data came from the Korean National Health Screening Program, and participants were followed until December 2023. Across 24.18 million person-years of follow-up, the team counted 35,887 new lung cancer cases and 12,807 lung cancer deaths. The researchers describe it as one of the largest studies of vaping after smoking cessation.
They sorted people into three groups: those who quit cigarettes and e-cigarettes entirely, those who switched to e-cigarettes, and those who kept smoking.
The numbers
Compared with complete quitters, former smokers who vaped daily had an adjusted hazard ratio of 1.56 for lung cancer. For death from lung cancer it was 2.00, so the risk of dying from the disease doubled.
People who kept smoking did worse. They had 1.78 times the risk of lung cancer and 2.41 times the risk of dying from it.
The gap was sharper among people already at high risk, those aged 50 to 80 with a smoking history of at least 20 pack-years. This is the group usually advised to have low-dose CT lung cancer screening. In that subgroup, vaping former smokers had 1.91 times the risk of developing lung cancer and 1.92 times the risk of dying from it.
The team adjusted for age, sex, smoking intensity, chronic lung disease, body mass index, income and physical activity. The link between e-cigarette use after quitting and higher lung cancer risk held up.
What the study cannot say
The researchers stressed that this was an observational study. It cannot prove e-cigarettes caused the cancers, only that continued vaping after quitting went along with worse lung cancer outcomes.
They also did not argue that vaping is worse than smoking. Continued smokers still had the highest risks overall. Their conclusion was narrower: the biggest cut in lung cancer risk comes from quitting both cigarettes and e-cigarettes. Vaping after quitting, they said, may erode some of the benefit that stopping smoking normally brings.
Smokers thinking about switching should talk to their doctor.
