The emergence of electronic smoking devices is a recent and scientifically underexplored phenomenon. These devices were initially thought of as a harm-reduction strategy in cigarette smokers, a purpose for which there is still no definitive evidence of effectiveness. Preliminary but consistent findings in the literature suggest the possibility of detrimental health effects to e-cigarette users. Despite being prohibited for sale in the country, electronic cigarettes are easily accessible, in an unregulated manner. The increasing number of users, approaching one million according to recent data, and the uncertainties regarding the composition, manufacturing quality, and potential long-term effects of exposure to the vapor they produce, make the use of electronic cigarettes an emerging issue in Brazilian public health. Based on the aforementioned issues, exploring the potential effects of this new health-related behavior is urgent. Thus, the present proposal describes a research project envisioning the execution of two interconnected studies: (1) an observational cross-sectional analysis, in an exposed-control design, evaluating general health parameters of electronic cigarette users compared to non-smoking control individuals, matched by sex and age; and (2) an intervention study nested within the first study, designed as a randomized clinical trial, with electronic cigarette users assigned to a group that will take a 7-day pause from using these devices, compared to a control group that will not undergo any intervention. The studies were designed with cardiorespiratory fitness - measured by a maximum exercise cardiopulmonary test (ergospirometry) - as the primary outcome. The sample size calculated for the cross-sectional study comprises 148 individuals (74 per group), and the intended sample for the randomized clinical trial consists of the 74 electronic cigarette users already recruited for the cross-sectional study. The secondary outcomes of both studies are related to cardiorespiratory parameters, pulmonary function (spirometry), vascular function (endothelial function and tissue oxygenation), cardiovascular risk (lipid profile and blood pressure), inflammatory markers, and anthropometric measurements. The statistical analyses will be performed using Analysis of Covariance (ANCOVA), with physical activity level as a covariate for the cross-sectional study, and Generalized Estimating Equations (GEE), with initial oxygen consumption value as a covariate for the clinical trial. The investigators expect that the proposed studies yield new and relevant information regarding the potential harmful effects of electronic cigarettes, as well as the possibility of reversing these effects through refraining from their consumption. The novelty of the studies, the urgency of the topic, the boldness of the experimental approaches, and the high immediate applicability of the findings are highlighted in this proposal, with the potential to support public health policies concerning this relevant issue.
