A large Korean study suggests people who use e-cigarettes after quitting analog smoking may see a reduction in the benefits that quitting usually brings.
A new study adds to the growing body of evidence that e-cigarette use isn’t as safe as manufacturers claim it to be.
The study, published in Nature Medicine, used data from the South Korean National Health Insurance Service Database, a nationwide data source that covers almost all healthcare episodes and test results, to explore the potential association between e-cigarette use after quitting smoking and the subsequent risk of lung cancer and death.
“Although epidemiological and biological studies support the association between e-cigarettes and various respiratory disorders, evidence regarding the relationship between e-cigarettes and lung cancer risk remains limited,” the researchers wrote.
“In particular, it is unclear whether e-cigarette use among former smokers is associated with future lung cancer risk. Relevant data are needed to determine the validity of e-cigarettes as a risk-reduction strategy for this population, who already face a substantially elevated risk of lung cancer.”
Data were extracted for over 4.5 million people who participated in the biennial health screening checks offered as part of the NHIS in 2018 and who were followed up until December 2023. Records of previous screening checks (2012 to 2014) were also accessed. Individuals who reported that they had never smoked or who had a previous diagnosis of lung cancer were excluded.
The 4.5 million individuals were allocated to one of five groups based on a combination of their smoking history and e-cigarette use. People who identified as smokers in 2012-2014 but indicated they were a former smoker in 2018 were defined as short-term smoking quitters, while people who said they were former smokers in both 2012-2014 and 2018 were classified as long-term smoking quitters.
There were current smokers (n = 2,319,857), short-term smoking quitters with e-cigarette use (20,496), short-term smoking quitters without e-cigarette use (767,273), long-term smoking quitters with e-cigarette use (5050), and long-term smoking quitters without e-cigarette use (1,412,220). The six-year follow-up period translated to 24,182,543 person-years. During this time there were 35,887 people diagnosed with lung cancer and 110,346 deaths – 12,807 of which were lung cancer-specific deaths.
After accounting for factors known to be associated with lung cancer risk and other relevant sociodemographic variables such as age, sex, pack-years smoked, BMI, alcohol consumption, and whether the person had underlying COPD or idiopathic pulmonary fibrosis, ex-smokers who went on to use e-cigarettes were more likely to develop lung cancer (adjusted hazard ratio and 95% confidence interval 1.56, 1.24-1.97) and die from lung cancer (2.00, 1.28-3.15) compared with former smokers who did not use e-cigarettes. Ex-smokers who became e-cigarette users also were more likely to die from any cause compared to ex-smokers who did not go on to use e-cigarettes (1.22, 1.05-1.41).
“The potential harms of e-cigarettes include acute pulmonary toxicity and lung carcinogenesis beyond the known effects of nicotine and its metabolites,” the researchers wrote. “Several studies have shown that e-cigarettes and heating elements contain carbonyl compounds (for example, formaldehyde, acetaldehyde, acrolein and diacetyl) and toxic metals (for example, chromium, nickel, and lead), which are known to be carcinogenic and also present in conventional cigarettes.”
When compared to current smokers, ex-smokers without e-cigarette use were less likely to develop lung cancer (0.56, 0.55-0.57) and to die from lung cancer (0.42, 0.40-0.43). Ex-smokers who became e-cigarette users were less likely to experience all-cause mortality compared to current smokers (0.77, 0.66-0.89).
The time since quitting smoking was also associated with lung cancer incidence and lung cancer-related deaths. The likelihood of lung cancer was higher in long-term quitters with e-cigarette use (1.74, 1.07-2.84) than in short-term quitters with e-cigarette use (1.31, 1.27-1.35) compared to long-term smoking quitters who did not go on to use e-cigarettes. A similar trend was observed for lung cancer-related deaths (2.57, 1.07-6.19 for long-term quitters who picked up e-cigarettes and 1.54, 1.46-1.62 for short-term quitters).
Examining the associations on older individuals (aged 50-80 years) with smoking history of 20 or more pack years revealed that people who used e-cigarettes after quitting smoking were more likely to develop lung cancer (1.91, 1.44-2.53) and more likely to experience lung cancer-related death (1.92, 1.13-3.24). There was no association with all-cause mortality between ex-smokers with and without e-cigarette use.
“Taken together, these findings suggest that, while e-cigarette use after quitting smoking may attenuate lung cancer-specific benefits of cessation, the broader health benefits of quitting conventional cigarettes are not eliminated,” the researchers said.
“Although e-cigarettes contain potentially carcinogenic substances, dual use may nonetheless be associated with lower cumulative exposure to toxicants than exclusive combustible cigarette smoking.
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“Nevertheless, these findings do not alter our primary conclusions regarding the association between e-cigarette use after smoking cessation and lung cancer risk.”
The research team acknowledged some of the key limitations of their work.
“First, we assessed e-cigarette use using available self-reported questionnaires, which may be subject to recall bias leading to potential misclassifications. Although our exposure definition is anchored to the exact wording of the 2018 NHIS questionnaire item that specifically asked about ‘electronic cigarette’ use, the 2018 instrument did not include a separate item to ascertain heated tobacco product (HTP) use because of the very recent introduction of HTPs in Korea (commercial availability beginning in June 2017),” they wrote.
“[In addition,] the relatively short follow-up duration may not sufficiently capture the long latency of lung cancer development and related outcomes, particularly among younger individuals with lower cumulative smoking exposure.
“For the general population, including persons with no smoking history, studies with longer follow-up and detailed assessments of other potential risk factors and biomarkers are needed to further evaluate the association between e-cigarette exposure and lung cancer risk.”
And while the findings of the new research cannot be considered causal, the researchers felt they painted a clear picture: “that e-cigarette use after smoking cessation may attenuate the benefits of complete cessation for lung cancer prevention”.
