The ESTxENDS Trial- Substudy on the Metabolic Effects of Using Electronic Nicotine Delivery Systems (ENDS/Vaporizer/E-cig)

--\> This is a substudy of the main ESTxENDS trial (NCT03589989). Metabolic outcomes should be considered secondary outcomes of the main smoking cessation outcome formulated in NCT03589989. Cardiovascular diseases (CVD) are a leading cause of death in cigarette smokers; quitting smoking is associated with reduced CVD. Cigarette smoking increases CVD through complex mechanisms, mostly on an increase in atherosclerosis and the effect appears unrelated to nicotine. Recently, electronic nicotine delivery systems (ENDS; also called vaporizer or electronic cigarette) have become popular with smokers who want to stop smoking. There is currently no evidence that ENDS use affects CVD outcomes. The nicotine contained in the e-liquids from ENDS has cardiovascular effects and the evidence about health effects mostly comes from studies on nicotine replacement therapy (NRT). These studies did not show an increased risk of CVD from NRTs. The ECLAT trial showed no difference in body weight, resting heart rate, or blood pressure between those who used ENDS or not. Two studies evaluated the short-term effects of ENDS on the cardiovascular system. One study suggested impairment in diastolic ventricular function with cigarettes and not with ENDS. Both ENDS and cigarettes increased diastolic blood pressure, potentially mediated through nicotine exposure, but an increased systolic blood pressure was found only in cigarette smokers. Other studies have suggested no changes in blood pressure in daily users of electronic cigarettes up to 1 year with some even a reduction in blood pressure among patients with hypertension. Interventions helping smokers quit have shown that quitting is associated with increased HDL-cholesterol, weight gain, higher blood glucose, and higher diabetes risk. No large randomized trials have tested the effect of ENDS on blood cholesterol and other markers of cardiovascular risk. This study will therefore test the efficacy of ENDS for cigarette smoking cessation, t