E-cigarettes may increase cardiovascular risk.

Eectronic cigarettes are becoming increasingly popular, but little is known about the risks they pose to cardiovascular health. New research investigates the link between habitual electronic cigarette use and cardiovascular risk.
More and more people use electronic cigarettes (e-cigarettes) instead of conventional ones, as the former are perceived to be safer. E-cigarettes do not contain tobacco and do not involve combustion.
E-cigarettes were first introduced in 2006 in the United States. Since then, they have become particularly popular among teens. The number of teenagers who vape increased fourfold between 2011 and 2015. However, e-cigarettes still contain the addictive nicotine and some of the chemicals found in regular cigarettes. In 2009, the U.S. Food and Drug Administration (FDA) warned that e-cigarettes contain "detectable levels of known carcinogens and toxic chemicals to which users could be exposed." New research examines the link between regular e-cigarette use and the implications for cardiovascular risk.
The sympathetic nervous system takes control of the cardiovascular system in "emergency" situations. It produces the "fight or flight" response when the individual is in danger, increasing the adrenaline levels in the heart. As for oxidative stress markers, the researchers found an increased level of low-density lipoprotein oxidizability. This indicates that lipoproteins containing the apolipoprotein B are prone to oxidation.
Overall, this means that compared with the control group, users of e-cigarettes were more prone to increased cardiac sympathetic activity and increased oxidative stress - both signs of tobacco-related cardiovascular risk. Therefore, habitual e-cigarette use has physiologic effects, many of which may seriously affect the users' cardiovascular health. The authors caution against the cardiac risks and recommend further investigation of the adverse health effects of inhalable nicotine. They say:
"Nicotine, which is the major bioactive ingredient in e-cigarette aerosol, with its metabolites, may harbor unrecognized, sustained adverse physiologic effects that lead to an increased cardiovascular risk profile in habitual e-cigarette users."