5 year longitudinal study finds e-cigs and cigs have similar risks for respiratory disease and COPD; dual use is worse

Beibei Song and colleagues’ new paper, Impact of electronic cigarette usage on the onset of respiratory symptoms and COPD among Chinese adults, finds that e-cigarettes and cigarettes pose similar risks for causing respiratory symptoms and chronic obstructive disease (COPD) in Chinese adults. Dual use is worse than using either product alone.

This is a very strong study. Song and colleagues recruited 10,326 Chinese adults who did not have respiratory disease or COPD and followed them forward in time for 5 years to see who developed these diseases. Participants were separated into people who just used smoked cigarettes, just used e-cigarettes, were dual users (both smoked and used e-cigarettes) and compared to people who did not use either product.

Adjusting for a range of demographic and clinical factors, using e-cigarettes and smoking cigarettes at baseline was associated with similar increases in risk of developing respiratory symptoms (e-cigarettes: OR 1.28, 95% CI 1.01–1.55; cigarettes: OR 1.23, 95% CI 1.03–1.43 ). Dual use was associated with about 10% higher risk than using either product alone (OR 1.41, 95% CI 1.19–1.61).

There were similar findings for COPD: (e-cigarettes: OR 1.08, 85% CI 1.02–1.64; cigarettes: OR 1.07, 1.00–1.25). Dual use was associated with about 10% higher risk (OR 1.18, 95% CI 1.01–1.39).

They also found a dose-response relationship, with more hours of e-cigarette use associated with higher disease risks.

The longitudinal design of the study, combined with the presence of a dose-response relationship increases the confidence we can have in concluding that the smoking and e-cigarette use caused the disease.

Another strength of this study is that the disease assessments were made with direct clinical observation of disease (as opposed to self-report of the diagnosis). The fact that the people were assessed in clinical exams also allowed the investigators to measure a wider range of clinical variables (such as blood lipids and blood pressure) than is possible in most epidemiological studies.

The finding of similar risks for using e-cigarettes and smoking differs from our recently-published meta-analysis (blog post; paper), which found lower risks of respiratory disease and COPD for e-cigarette users compared to smokers. The levels of risk (ORs compared to non-use) was similar (in the sense that the 95% CIs overlapped) in the new Chinese study to that estimated in our meta-analysis (OR 1.46, 95% CI 1.31-1.61) for COPD. The smoking and dual use ORs in the Chinese study were lower than in our meta-analysis (, , while significantly elevated, were lower in the new Chinese than in our meta-analysis (cigarettes: 2.99, 95% CI 2.29–3.92; dual use: 3.29, 95% CI 1.97–5.51). Both the new Chinese study and our meta-analysis found that dual use was associated with higher risk than using e-cigarettes or smoking alone (OR 1.41 95% CI 1.12–1.64 in the meta-analysis).

The finding that dual use has higher risks than just using e-cigarettes or just smoking is particularly important because 55% of the e-cigarette users (187/343) were dual users.

The authors provide an excellent summary of the biology on how e-cigarettes cause these effects:

The laboratory experiments consistently demonstrate the potential biological impact of EC [e-cigarette] usage on the development of respiratory symptoms and COPD. The available laboratory findings indicate that EC use primarily affects respiratory health through four distinct biological mechanisms: cellular toxicity, heightened oxidative stress, increased vulnerability to infections, and genetic alterations. The concentrations of various pulmonary toxic substances in EC aerosol, including propylene glycol, diacetyl, cinnamaldehyde, benzaldehyde, and metals, are comparatively elevated when compared to their levels in traditional cigarettes. The cytotoxic effects and oxidative stress observed were attributed to the repeated exposure of cells to harmful substances released during the heating process of electronic liquid in EC devices. The results obtained from experiments conducted on living organisms as well as in laboratory settings indicate that the presence of EC leads to an enhancement in the potency of bacteria and their vulnerability to infections. Additionally, studies using animal models have revealed that exposure to EC aerosol worsens the rates of illness and death associated with both bacterial and viral infections. The aerosol from ECs, unlike combusted tobacco smoke, has been found to increase the risk of cell death and DNA damage while also suppressing genes involved in immune function. According to the biological evidence, our study findings demonstrate that the use of ECs independently contributes to an increased risk of respiratory symptoms and COPD. Notably, individuals who engage in dual use of ECs and combustible cigarettes face a higher risk for developing incident respiratory symptoms and COPD compared to those who exclusively use either cigarette type. These findings align with the results observed in our study consensus reports on this topic should be noted as well. It is worth mentioning that dual users of both ECs and combustibles, which represents the most common usage pattern, face an even greater risk for respiratory symptoms and COPD than those who solely use either product alone. Therefore, it is crucial for policymakers responsible for smoking cessation efforts worldwide to pay closer attention to regulating not only individual users of ECs but especially those who engage in dual usage alongside traditional combustible cigarettes according to recommendations made by the World Health Organization. [citations deleted]

Here is the abstract:

The prevalence of dual usage and the relatively low cessation rate among e-cigarette (EC) users suggest that ECs have not demonstrated significant effectiveness as a smoking cessation tool. Furthermore, there has been a substantial increase in the prevalence of EC usage in recent years. Therefore, the objective of this study is to investigate the association between EC use and the incidence of respiratory symptoms and chronic obstructive pulmonary disease (COPD). A total of 10,326 participants aged between 20 and 55 years, without any respiratory diseases or COPD, were recruited for the study. These individuals attended employee physical examinations conducted at 16 public hospitals in Hebei province, China from 2015 to 2020. Logistic regression models were utilized to assess the association between EC use and the risk of respiratory symptoms and COPD using risk ratios along with their corresponding 95% confidence intervals. Restricted cubic spline functions were employed to investigate the dose-response non-linear relationship. The robustness of the logistic regression models was evaluated through subgroup analyses, and sensitivity analyses. During the 5-year follow-up period, a total of 1071 incident cases of respiratory symptoms and 146 incident cases of COPD were identified in this cohort study. After adjusting for relevant confounding factors, EC users demonstrated a respective increase in the risk of reporting respiratory symptoms and COPD by 28% and 8%. Furthermore, dual users who used both ECs and combustible cigarettes exhibited an elevated risk of incident respiratory symptoms and COPD by 41% and 18%, respectively, compared to those who had never used non-users of any cigarette products. The association between daily EC consumption and the development of respiratory symptoms, as well as COPD, demonstrated a significant J-shaped pattern. The potential adverse association between the consumption of ECs, particularly when used in combination with combustible cigarettes, and the development of respiratory symptoms and COPD necessitates careful consideration. Policymakers should approach ECs cautiously as a prospective smoking cessation tool.

The full citation is: Song B, Li H, Zhang H, Jiao L, Wu S. Impact of electronic cigarette usage on the onset of respiratory symptoms and COPD among Chinese adults. Sci Rep. 2024 Mar 7;14(1):5598. doi: 10.1038/s41598-024-56368-9. PMID: 38454045; PMCID: PMC10920732. It is available here.