Abstract
Introduction
E-cigarettes are perceived as a less harmful alternative to conventional cigarettes; however, concerns remain about the potential health risks associated with long-term use. This systematic review and meta-analysis aimed to assess the long-term effects of e-cigarettes on airway inflammation, as measured by fractional exhaled nitric oxide (FeNO).Methods
This is a systematic review and meta-analysis. MEDLINE and EMBASE were searched via Ovid, with the last search conducted on 3 October 2025. Studies were included if they used FeNO to assess the effects of long-term e-cigarette use; those without FeNO measurements were excluded. Risk of bias was assessed with validated tools according to study design, and meta-analysis was performed when quantitative data were available. The protocol was prospectively registered in PROSPERO (CRD42024508780).Results
From 1018 records, six studies (n=792 participants) met the eligibility criteria. The included studies varied in population characteristics and findings: one reported higher FeNO in complete quitters versus failures/reducers; two found higher FeNO in e-cigarette users versus controls; two observed no difference; and one found lower FeNO among e-cigarette users. The meta-analysis of three studies showed a pooled mean difference of -0.26 (95% CI: -9.74-9.22), indicating no significant difference between groups.Conclusions
The results across studies were heterogeneous and inconclusive, highlighting the variability in findings related to the impact of long-term e-cigarette use on airway inflammation. These inconsistencies underscore the need for further research, particularly well-powered longitudinal prospective studies, to better understand the long-term effects of e-cigarette use on inflammatory biomarkers such as FeNO.