Researchers have found that industry claims about the e-cigarettes are unsupported by the evidence to date and that they may be exposing people to more than harmless vapor.

The study also disapproved claims that said e-cigarettes help smokers quit.

The review marks the first comprehensive assessment of peer-reviewed published research into the relatively new phenomenon of electronic cigarettes.

The devices, which are rapidly gaining a foothold in popular culture particularly among youth, are marketed as a healthier alternative to tobacco smoking, as an effective tool to stop smoking, and as a way to circumvent smoke-free laws by allowing users to "smoke anywhere." Often the ads stress that e-cigarettes produce only "harmless water vapor."

But in their analysis of the marketing, health and behavioral effects of the products, which are unregulated, the UCSF scientists found that e-cigarette use is associated with significantly lower odds of quitting cigarettes.

They also found that while the data are still limited, e-cigarette emissions "are not merely 'harmless water vapor,' as is frequently claimed, and can be a source of indoor air pollution."

The long-term biological effects of use are still unknown, the authors said.

In tackling the question of whether e-cigarette use is helping or harming the nation's tobacco control efforts, the authors analyzed 84 research studies on e-cigarettes and other related scientific materials.

They concluded that e-cigarettes should be prohibited wherever tobacco cigarettes are prohibited and should be subject to the same marketing restrictions as conventional cigarettes.

The paper has been published in the American Heart Association's journal Circulation.