Vascular health after quitting smoking or switching to e-cigarette use: a systematic review of prospective studies with GRADE assessment

Objectives: This systematic review aims to evaluate the effects of smoking cessation or switching to exclusive electronic cigarette (EC) use on vascular function in adult smokers, using prospective evidence from clinical studies. Methods: A comprehensive literature search was conducted in PubMed, Scopus, Web of Science and Embase on Oct 13, 2025. Eligible studies included randomized controlled trials (RCTs), quasi-experimental designs, and prospective cohort studies reporting quantitative or narrative data on vascular outcomes (i.e., pulse wave velocity (PWV), augmentation index (AIx), and flow-mediated dilation (FMD)), after smoking cessation or switching to ECs. Risk of bias was assessed using the Joanna Briggs Institute tools. Results were synthesized qualitatively. Certainty of the evidence was determined using GRADE (Grading of Recommendations, Assessment, Development, and Evaluation). Results: Twenty-three studies involving a total of 11,702 participants were included: 14 cohort studies, 5 quasi-experimental and 4 RCTs. Overall, smoking cessation was consistently associated with improvements in PWV, AIx, and FMD, with some effects observable within one month and sustained up to 24 months. The overall certainty of evidence was very low, except for a moderate level of certainty derived from RCTs investigating FMD. Improvements were seen across different cessation methods, including pharmacotherapy and ECs. RCTs on ECs reported significant improvements in FMD irrespective of nicotine content, suggesting that combustion rather than nicotine may be the primary driver of vascular impairment. Sensitivity analyses excluding lower-quality RCTs confirmed the primary findings. Conclusions: Smoking cessation appears to improve vascular function, as reflected by early favorable changes in endothelial and arterial stiffness markers; however, the overall certainty varies from moderate to very low, according to the outcome. These findings are consistent with the biological plausibility of cardiovascular benefit from sustained smoking abstinence.