Whether electronic cigarettes will ultimately help or hurt the health of the U.S. and UK populations isn't yet clear, researchers say.
There may be a health benefit if only current or future smokers begin using the devices – but health may suffer if so-called e-cigarettes made smoking common again, they report in JAMA Internal Medicine.
Outcomes in more complex scenarios, which include current and never smokers using e-cigarettes, will depend on the as-yet-unknown health effects of e-cigarettes, said lead author Dr Sara Kalkhoran, of the University of California, San Francisco (UCSF).
Nicotine vapour inhaled
"Given the relatively recent emergence of e-cigarettes on the market, it is not yet clear which of these scenarios will ultimately play out," Kalkhoran told Reuters Health in an email.
Read: We try the e-cigarette
E-cigarettes emerged in Europe and North America between 2006 and 2008. The battery-powered devices turn liquid containing nicotine into vapour, which the user inhales.
E-cigarettes don't contain many of the harmful chemicals found in traditional cigarettes, but there are no studies on the long-term use of the devices.
For the new study, researchers used computers to simulate various scenarios of cigarette and e-cigarette use.
"Looking at separate U.S. and UK models was interesting as we did not know how the results would compare," Kalkhoran said.
Differences between the two nations' scenarios suggest that current smoking patterns are important to what happens to the nation's overall health later on, she said.
Under the most likely scenarios, there will be a net harm if e-cigarettes are 20 to 30 percent as dangerous as traditional cigarettes, said senior author Stanton Glantz, of the Centre for Tobacco Control Research and Education at UCSF.
A lot of confusion
"I would be surprised if the risks are not at least that high," he told Reuters Health in an email.
Kalkhoran said the findings model a number of different scenarios at a time when policymakers and regulatory agencies are under pressure to make decisions about e-cigarettes.
Earlier this month, a study from the UK's Department of Health backed the use of e-cigarettes by saying they're 95 percent safer than tobacco equivalents.
The findings contradicted recent calls from the World Health Organisation and other regulatory bodies to restrict use of the devices.
"I think the biggest point is that there is a lot of confusion about the harm level of these products," said Robert McMillen, of Mississippi State University in Starkville.
Until more is known, people should be cautious about exposure to the vapours of e-cigarettes and doctors should be cautious about recommending the products, said McMillen, who co-authored an editorial accompanying the new study.
SOURCE: http://bit.ly/1X69TK9 JAMA Internal Medicine, online August 31, 2015.