(HealthDay)

MONDAY, June 2, 2014 (HealthDay News) -- Commercials that promote electronic cigarettes have become a growing presence on American TV, new research finds, with the youth audience for such ads roughly tripling in recent years.

The upshot: E-cigarettes are now being pitched to roughly 24 million viewers between the ages of 12 and 24, the study authors said.

The findings raise concerns about the promotion and popularity of e-cigarettes, given the range of unanswered questions regarding their safety.

"The is the first piece of evidence to show exactly how much e-cigarette advertising our youth is seeing," explained study author Jennifer Duke, a senior research public health analyst with RTI International in Research Triangle Park, N.C. "And what we found is that while in 2010 e-cigarette advertising on TV was very limited, the increase since that time has been very dramatic."

"Now, the manufacturers say that they are not targeting youth," Duke noted. "But the truth is that it's impossible on a medium like TV to increase ad exposure to this degree and not increase exposure to youth. And it's also clear that the increase in advertising is specifically happening on shows and cable networks that are very popular with youth."

Duke and her colleagues report their findings online June 2 and in the July print issue of Pediatrics.

Duke pointed out that while TV advertising for traditional cigarettes has been banned since 1971, the U.S. Food and Drug Administration only regulates e-cigarettes when they are specifically marketed as smoking-cessation devices.

The FDA in April proposed long-awaited regulations governing the fast-growing electronic cigarette industry.

The new rules would give the FDA the authority to regulate e-cigarettes as tobacco products, placing them under the same requirements as cigarettes. That would include a ban on the sale to minors.

E-cigarettes are essentially nicotine-delivery systems that rely on battery-powered heating mechanisms to vaporize chemicals for easy inhaling. And although e-cigarettes are usually designed to mimic the appearance of a traditional cigarette, they are distinguished by a smokeless environment that does away with the need for burning tobacco.

Federal health experts caution that the safety of e-cigarettes remains unclear until more rigorous studies are conducted. And they stress that the absence of toxic combustion does nothing to undercut the highly addictive nature of nicotine itself. Nor is it yet clear what level of threat may be posed by other carcinogenic chemicals commonly found in e-cigarette vapor.

To evaluate current e-cigarette advertising trends on TV, the study authors reviewed information provided by Nielsen, the main collector of TV advertising data.

Focusing on the years 2011 through 2013, the study team tracked all the e-cigarette advertisements that aired on more than 100 network and cable channels across 210 different markets.

The result: the number of children between 12 and 17 who were exposed to e-cigarette ads on TV rose more than 250 percent between 2011 and 2013.

Among young adults between 18 and 24, that increase amounted to more than 320 percent.

More than three-quarters of the ads were airing on networks known to be popular with young people, including Comedy Central, TV Land, WGN America, VH1, Country Music Television and AMC.

"I would say that we don't know what exposure to e-cigarettes will do over time," Duke acknowledged. "We don't yet know if they are a pathway to use of traditional cigarettes themselves. But we do know the negative effect nicotine has on brain development among youth. So it's a real concern. And given the potential dangers, I certainly think the FDA should regulate images of e-cigarettes on TV and other places where they do advertising, just as they already do for regular cigarettes."

Dr. Norman Edelman, senior medical advisor for the American Lung Association, said that growth in e-cigarette advertising isn't particularly surprising.

"As e-cigs enter the 'mainstream' and are produced by bigger manufacturers, they are more likely to be promoted by the more expensive but more widely accessed major media, such as cable TV," he said. "[And] there seems little doubt that the makers will consider teenage children as a major market and will market to them, albeit indirectly by indicating that they are 'for adults.' "

Edelman said the attempt to place e-cigarettes before a wide audience of young Americans is a troublesome development.

"There is little doubt that inhalation of nicotine embedded in chemically active vapor vehicles causes at least some harm," he added. "Whether it causes as much harm as tobacco smoke is a complex and unresolved question, which might be relevant to adult smokers. However, it is not relevant for children, who will not use the device as a replacement for tobacco smoke but as an initiation to nicotine inhalation -- a highly addictive substance with deleterious biologic effects in the doses associated with e-cigs."

"Clearly it is important that we develop policies to protect children from this potential threat," Edelman said.

More information

For more information on e-cigarettes, visit the U.S. National Institute on Drug Abuse.