Emissions from most, but not all, electronic cigarettes were more than 100 times less carcinogenic than emissions from traditional combustible cigarettes, according to a British study.
Most of the e-cigarettes tested had cancer causing potencies falling within two orders of magnitude of a medicinal nicotine inhaler devices, but a "small minority" had much higher potencies, wrote William E. Stephens, PhD, of the University of St. Andrews in Fife, Scotland.
But "high-risk results tend to be associated with high levels of carbonyls generated when excessive power is delivered to the atomiser coil," he wrote in Tobacco Control.
Stephens modeled the cancer potencies of a range of e-cigarettes and other nicotine-delivering aerosols using published chemical analyses of emissions and their associated inhalation unit risks.
Potencies were compared using a conversion procedure for expressing smoke and e-cigarette vapors in common units, and lifetime cancer risks were calculated associated with various potencies using daily cancer consumption estimates.
"Many electronic e-cigarette emissions have cancer potencies within an order of magnitude of a nicotine inhaler, a product generally regarded as safe," Stephens wrote. "Notwithstanding, some e-cigarette emissions tended towards much higher cancer potencies and risks, a few possibly approaching those of tobacco smoke."
Based on the analysis, he concluded that the cancer potency of formaldehyde, which is the most significant e-cigarette carcinogen, may exceed that of tobacco smoke in some products, especially at the highest power settings.
The range of cancer potencies identified in the study spanned four orders of magnitude, with "the vast majority of potencies being much lower than combustible cigarettes," Stephens noted.
"It is likely that third/fourth generation e-cigarette devices with adjustable coil power are implicated in these higher risks," he wrote, adding that with regard to involuntary exposure to e-cigarette emissions, "greater understanding of potential effects of secondhand e-cigarette exposure is needed to determine if their use in indoor public spaces should be banned, as is currently the case in 25 countries."
In a telephone interview with MedPage Today, Stanton Glantz, PhD, of the University of California San Francisco Center for Tobacco Control and Research Education, called the study well done, adding that it adds to the already-convincing literature showing e-cigarettes to be associated with much lower carcinogenic exposures than combustible cigarettes.
"To me, it's sort of beating a dead horse," he said. "The fact is, I don't know anyone who thinks that e-cigarettes don't deliver carcinogens at a much lower level than conventional cigarettes. They don't have combustion and the combustion process generates a lot of carcinogens."
But he added that the jury is still out on other potential risks of e-cigarettes, and other vaporized nicotine delivery, for non-malignancy related diseases associated with smoking, including heart disease, non-cancer lung disease, and diabetes.
He said the early research suggests that e-cigarette use, like traditional smoking, may be a major risk factor for these diseases, which are linked to more smoking-related deaths than cancer.
Study limitations included the use of emissions data, which can both overestimate and underestimate risk, and the inclusion of only carcinogens formally classified by the International Agency for Research on Cancer (IARC) in the analysis.
Carcinogenicity of secondhand vapor was also not specifically addressed in the study.
