IMPORTANCEThe electronic cigarette (EC) has become popular among smokers who wish to reduce their tobacco use levels or quit smoking, but its effectiveness as a cessation aid is uncertain.OBJECTIVE To examine the association of regular EC use with the number of cigarettes smoked per day, smoking cessation among current smokers, and smoking relapse among former smokers. DESIGN, SETTING, AND PARTICIPANTSThe CONSTANCES (Consultants des Centres d'Examens de Santé) cohort study, based in France, began recruiting participants January 6, 2012, and is currently ongoing. Participants were enrolled in CONSTANCES through 2015, and included 5400 smokers (mean [SD] follow-up of 23.4 [9.3] months) and 2025 former smokers (mean [SD] follow-up of 22.1 [8.6] months) at baseline who quit smoking in 2010, the year in which ECs were introduced in France, or afterward. Analyses were performed from February 8, 2017, to October 15, 2018. MAIN OUTCOMES AND MEASURESThe association between EC use and the number of cigarettes smoked during follow-up was studied using mixed regression models. The likelihood of smoking cessation was studied using Poisson regression models with robust sandwich variance estimators. The association between EC use and smoking relapse among former smokers was studied using Cox proportional hazards regression models. All statistical analyses were adjusted for sociodemographic characteristics, duration of follow-up, and smoking characteristics. RESULTSAmong the 5400 daily smokers (2906 women and 2494 men; mean [SD] age, 44.9 [12.4] years), regular EC use was associated with a significantly higher decrease in the number of cigarettes smoked per day compared with daily smokers who did not use ECs ] vs -2.7 [95%CI, -3.1 to -2.4]), as well as a higher adjusted relative risk of smoking cessation (1.67; 95%CI, 1.51-1.84]). At the same time, among the 2025 former smokers (1004 women and 1021 men; mean [SD] age, 43.6 [12.1] years), EC use was associated with an increase in the rate of smoking relapse among former smokers (adjusted hazard ratio, 1.70; 95%CI, 1.25-2.30).CONCLUSIONS AND RELEVANCE This study's findings suggest that, among adult smokers, EC use appears to be associated with a decrease in smoking level and an increase in smoking cessation attempts but also with an increase in the level of smoking relapse in the general population after approximately 2 years of follow-up.

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Evidence map of the association between urological cancer and air pollutants. The left panel shows the total number of studies (number of ecological studies between parentheses), color-coded based on number of available studies (from light green for 1 to dark green for 4). The right panel shows, for bladder cancer, the strength of the evidence assessed for each individual studies using the New-Castle Ottowa score (NOS) as y-axis (here we present the average of the NOS by pollutant and outcome, and the line depicts a NOS of 6, our cut-off to define good-quality articles), and for each pair of outcome-pollutant using the GRADE approach.The results of this review showed a suggestive association between kidney and bladder cancer risk and air pollution, however the conclusions are based on few studies and most of them with a low GRADE score.