E-cigarette Use and Subsequent Tobacco Smoking Initiation: An Umbrella Review with Bayesian Model Me

Kaur J, Goel S, Shabil M, Gupta S, Rana RK, Rinkoo AV, Chauhan A.
E-cigarette Use and Subsequent Tobacco Smoking Initiation: An Umbrella Review with Bayesian Model Meta-analysis
Tob Control. 2026 Feb 26:tc-2025-059783. doi: 10.1136/tc-2025-059783. Epub ahead of print. PMID: 41748427.

Objective: Electronic nicotine delivery systems (ENDS) have seen a global surge in their usage. However, their role in smoking initiation, particularly among non-smokers, remains a critical concern. This umbrella review evaluated the risk of tobacco-smoking initiation following ENDS use, focusing on non-smokers, by synthesising evidence using Bayesian meta-analysis.

Study design: Systematic review and Bayesian meta-analysis.

Methods: We searched databases including PubMed, EMBASE and Cochrane Library up to 1 May 2025. We included systematic reviews assessing tobacco-smoking initiation after ENDS use among non-smokers. Quality was evaluated using the AMSTAR-2 (A Measurement Tool to Assess Systematic Reviews - version 2). A Bayesian hierarchical meta-analysis was conducted to estimate pooled ORs with 95% credibility intervals (CrIs), using non-informative priors to model heterogeneity and uncertainty. This study was registered with PROSPERO (CRD42023464207).

Results: From 5055 records, 13 systematic reviews were included. Of them, five were rated as 'high quality', one as 'moderate', four as 'low' and 'three' as critically low, as per AMSTAR-2 quality assessment. The meta-analysis revealed a pooled median OR of 3.1 (95% CrI 2.56 to 3.72) for smoking initiation among non-smoking ENDS users, with moderate heterogeneity (τ mean: 1.23). Among adolescents, the OR was 2.7 (95% CrI 2.27 to 3.21), with moderate heterogeneity (τ mean: 0.63). The risk of relapse in former tobacco smokers who used ENDS was doubled (RR: 2.03, 95% CI 1.39 to 2.96). Individuals who had never smoked but engaged with ENDS had more than twice the odds of developing an intention to smoke, with an OR of 2.21 (95% CI 1.86 to 2.61). The overall certainty of the evidence was rated very low due to the risk of bias in the studies and evidence of publication bias across the studies.

Conclusions: ENDS use is significantly associated with increased risk of tobacco smoking initiation among non-smokers, particularly adolescents, supporting the gateway hypothesis. These findings indicate the need for stringent regulatory and public health strategies to protect people from nicotine addiction.