The flavorings used in e-cigarettes might potentially be the most toxic part of the vapor inhaled by users, a new study suggests.
E-cigarette liquid contains dozens of different chemicals, and these vary widely from product to product, said lead author Flori Sassano. She is a research project manager with the University of North Carolina School of Medicine.
Many of these chemicals are toxic to human cells in the laboratory, but the most toxic appear to be those related to the flavorings contained in e-liquids, Sassano said.
These chemicals include vanillin and cinnamaldehyde, which respectively produce the flavors of vanilla and cinnamon.
The flavorings have been approved by the U.S. Food and Drug Administration for consumption, but that doesn't mean they are safe to inhale as vapor from an e-cigarette, Sassano explained.
The FDA's list of safe flavorings "is based upon studies that have been done of these chemicals when ingested, but not when inhaled," she said.
There are more than 7,700 e-liquid flavors on the market from more than 1,200 different vendors, and most have not been tested for their potential toxicity, the study authors said in background notes.
For their research, Sassano and her colleagues tested about 150 commercially available e-liquids, and out of those identified 143 unique chemical compounds.
"What this tells us is these e-liquids are very diverse, and because they are diverse they are very hard to study as a group," Sassano said.
To test toxicity, the researchers developed a system by which lab-grown human cells are exposed to e-liquid chemicals. The more toxic a chemical, the more it will reduce the growth rates of these cells, according to the report.
Most of the liquid in an e-cigarette is made up of propylene glycol and vegetable glycerin, and those chemicals on their own are toxic to lab-grown human cells, the researchers said.
But the flavorings added to e-cigarettes can be even more toxic, the investigators discovered.
The toxic effects of these liquids proved harmful to cells from human lungs and upper airways. And, overall, the more ingredients included in an e-liquid, the greater the toxicity, the findings showed.
The study was published online March 28 in the journal PLOS Biology.
Sassano said the process they've developed provides a fast and reliable way to evaluate the toxicity of the chemicals in e-liquids.
However, it's too soon to tell whether this means regular e-cigarette use will have long-term health consequences, said Sassano and Dr. Norman Edelman, senior scientific advisor to the American Lung Association.
"These are cell cultures," Edelman explained, "so it's a little bit of a leap of faith to translate that into human disease."
At the same time, this process is regularly used by the pharmaceutical industry to test the effects of new drug compounds, Sassano and Edelman noted.
In fact, Sassano said, "This approach is one of the most popular approaches in pharmaceutical companies. When you have a drug that you think might make it to the market, most of the time they go through these same kind of tests to identify the molecules that will be effective on the disease you are studying."
Gregory Conley, president of the American Vaping Association, said the "next steps in this process must not only include testing cigarette smoke in their systems, but validating the system to determine if what happens in cell dishes actually takes place in animals and humans."
According to Conley, "Had the authors compared the effects of cigarette smoke against the referenced vaping products, the results would demonstrate that cigarettes are magnitudes more toxic than the tested products. Regrettably, this was not done, and as a result the study sends the reckless and incorrect message to adult smokers that vaping may confer dangers similar to continued smoking."
But, Edelman said, these study results show that e-cigarettes are not harmless.
"You certainly can't say e-cigarettes are safe," Edelman said. "You always look at a risk/benefit analysis. If we were delivering lifesaving drugs using those liquids, you might say the risk is worth the benefit. But we're not delivering anything worthwhile. We're delivering nicotine that hooks kids."
The U.S. National Institute on Drug Abuse has more about e-cigarettes.
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