ABSTRACT
INTRODUCTION: This study aims to address the existing gap in the literature, while adding evidence, by comparing tobacco-specific biomarkers (cotinine and nitrosamines: NNK, NNAL, NNN), and other biomarkers of e-cigarette use (humectants: glycerol, 1,2-PD, 1,3-PD) according to five study groups. METHODS: A pooling analysis including two different studies was conducted. In both analyses, we took saliva samples from smokers (n = 409) and non-smokers (n = 154), dual tobacco and e-cig users (n = 92), exclusive e-cig user with nicotine (n = 158), and exclusive e-cig users without nicotine (n = 38). We analyzed and compared the geometric means (GM) and geometric standard deviations (GSD) of the concentration of tobacco-specific biomarkers, and e-cigarette biomarkers among groups. We used log-linear models adjusted for sex and age to model the change percentage and their 95% confidence intervals. RESULTS: Cotinine was significantly higher in nicotine consumers and in e-cigarette users without nicotine when compared to non-smokers. TSNAs were generally significantly lower in non-smokers and higher in nicotine consumers. NNN and NNAL were lower in e-cigarette users with nicotine comparted to smokers, and NNN was higher in e-cigarette users without nicotine when compared to non-smokers. No differences were found in humectant biomarkers between e-cigarette groups. CONCLUSIONS: Although there was a reduction in TSNAs in e-cigarette exclusive users compared to smokers, and a reduction of cotinine concentrations in e-cigarette exclusive users without nicotine compared to smokers, there are still high levels of these biomarkers when compared to non-smokers, which may be a clue towards the harmful effect of e-cigarettes.