A systematic review comparing the health effects of dual use of electronic and conventional cigarettes with health effects of exclusive smoking of conventional cigarettes

Abstract

Background: A high prevalence of dual use (DU) of e-cigarettes and conventional cigarettes has been reported across the world. In some countries most users of e-cigarettes are dual users (DUs). We wanted to investigate the health effects of DU and compare with the health effects of exclusive smoking of conventional cigarettes (ESCC). Methods: A systematic search was carried out in PubMed, EMBASE, CINAHL, and Cochrane library. The last search was conducted on April 26, 2021. We included original articles on any topic relevant to health, in all languages. Reviewers independently assessed the main risks of bias without the use of automated tools. We followed the PRISMA guidelines. Both reviewers independently screened and read all publications. Results: Fifty-five publications (52 studies) were included, 12 of the studies were prospective. There was great heterogeneity across studies both in methodology and outcome. Several studies, especially experimental studies with short-term outcome, found higher levels of harmful substances in ESCC than in DUs, however, the two largest population-based studies, with low risk of selection-bias, found higher levels of harmful substances in DUs than in ESCC. Most studies investigating symptoms or risk of disease were large population-based surveys. One study found that DUs reported a significantly better health than ESCC, while fifteen found a higher risk of e.g., pulmonary, cardiovascular or metabolic risk factors/symptoms, self-reported general health or cancer in DUs than in ESCC. The study with the longest follow-up, six years, found that DUs had an adjusted odds ratio of 1.48 (95% confidence interval 0.81–2.70) of a possibly smoking-related disease (confirmed by hospital discharge abstracts) compared with ESCC. Many methodological weaknesses were identified, such as risk of reverse causality. We found a correlation between high tobacco consumption in DUs and findings of negative health outcomes.Conclusion: Due to many methodological weaknesses, it is difficult to draw any strong conclusions, but the results indicate that DU might be as or even more harmful than ESCC. Well-designed longitudinal studies are needed. Before recommending EC for smoking cessation health authorities should consider the high risk of DU and its potential consequences.

E‐cigarette use by people who smoke or have recently quit, New South Wales, 2016–2020

“…Many reported dual use of tobacco and e‐cigarettes; 25% of users said they used e‐cigarettes to reduce (but not quit) smoking, and 8% that they used e‐cigarettes where smoking was not allowed. Methodological weaknesses in studies of the health impacts of using both e‐cigarettes and smoked tobacco make it difficult to draw conclusions about whether dual use is associated with health benefits or increased harm 23 . There is no evidence that dual use to reduce the amount of tobacco smoked is likely to lead to quitting 24 …”

Die E-Zigarette – Mittel zur Tabakentwöhnung?

“…In einer Langzeitbeobachtung über 6 Jahre ist das erhöhte Risiko bei Dual Usern für Rauch-assoziierte Erkrankungen erhöht (OR 1,48). Trotz methodischer Schwächen in den inkludierten Studien kommt eine aktuelle Übersicht zu der Schlussfolgerung, dass Dual Use mindestens genauso, wenn nicht sogar schädlicher ist als der ausschließliche Konsum konventioneller Filterzigaretten [20].…”