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Cinnamaldehyde is the biochemical that gives cinnamon its distinctive flavor and smell, and it has been approved as a food additive by the U.S. Food and Drug Administration.
But inhaling the chemical as part of heated e-cigarette vapor appears to inhibit a key mechanism of the lungs' antibacterial defense mechanism, researchers reported Wednesday at the American Thoracic Society's annual meeting, in San Diego.
Exposure to cinnamaldehyde reduces the beating of cilia, tiny hairlike projections that clear mucus and dirt from the lungs, the researchers found.
"Based on the research we and several other groups have conducted, inhaling cinnamon-flavored e-liquids will likely have several adverse effects on the lung," said senior researcher Ilona Jaspers. She's a professor of pediatrics and microbiology and immunology at the University of North Carolina School of Medicine.
For this study, Jaspers and her colleagues exposed lab-grown human lung cell cultures to both e-liquids and e-liquid vapors that contained cinnamon flavoring.
They found that the cilia in the lung cells experienced significantly reduced function following exposure to cinnamaldehyde.
The cilia work as an essential "mucus escalator" in the lungs, said Dr. Norman Edelman, senior scientific adviser to the American Lung Association.
"If you breathe in dust or bacteria, your lung engulfs it in mucus and then you have to get the mucus up and out. That's what these cilia do," Edelman said. "They beat in a wavelike coordinated fashion until those little drops of mucus make their way to your throat so you can cough them out."
Even though cinnamaldehyde is an FDA-approved food additive, inhaling the chemical can have very different consequences for the body compared to eating it, Jaspers said.
"When it gets ingested as a food, it undergoes a very different route of exposure through the GI tract," Jaspers said.
"The stomach is able to process cinnamon and/or cinnamaldehyde in a very different way than the lung. In general, changing the route of exposure from ingestion to inhalation can significantly affect the toxic potential of any compound, including food flavorings," she said.
Cinnamaldehyde also is more likely to be present in high concentrations in e-cigarette vapor, as opposed to the small amount a person might inhale while working with cinnamon in the kitchen, Jaspers added.
"One of the guiding principles in toxicology is 'the dose makes the poison,'" she said. "Inhaling a pinch of cinnamon is considerably different than inhaling cinnamaldehyde" from a flavored e-cigarette.
Jaspers would recommend that vapers stay away from cinnamon-flavored e-liquids, except that the flavoring's use is "ubiquitous," and e-liquids are not required to label their ingredients.
"The biggest problem is that nobody knows what flavoring chemicals are contained in the different e-liquids," Jaspers said. "Unless e-liquids have obvious names that indicate they are cinnamon-flavored, the consumer has no way of knowing whether e-liquids do or do not contain any or high levels of cinnamaldehyde."
The study provides more evidence that "the stuff in vaping fluid is not benign," Edelman concluded.
"It has all sorts of toxic potential for lung health," he said.
In a statement, the American Vaping Association, a trade group of e-cig makers, said, "Real-world evidence continues to show that adult smokers who switch to vaping experience the same or vastly similar lung health benefits as smokers who quit with other methods."
Until it has been published in a peer-reviewed medical journal, research presented at meetings should be considered preliminary.
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