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A common cinnamon food additive that is widely used to flavor e-cigarettes had harmful effects on human lung cells in a laboratory culture, disrupting the cells’ innate host defense system, scientists report.

The compound, called cinnamaldehyde, gives cinnamon its characteristic flavor and smell and is generally considered safe when added to food. But like many chemicals in e-cigarette emissions, it has not been thoroughly evaluated for safety when inhaled rather than ingested, said Phillip Clapp, who recently completed his doctorate in the lab of Dr. Ilona Jaspers, deputy director of the University of North Carolina at Chapel Hill’s Center for Environmental Medicine, Asthma and Lung Biology.

The researchers exposed cultured human bronchial cells to diluted cinnamon e-liquids and to e-liquid aerosol, or vapor, from an e-cigarette device purchased at a local vape shop in Chapel Hill. A single exposure impaired the function of the cells’ cilia, important hairlike projections whose back-and-forth movements clear mucus and pathogens from the lungs.

Anything that impairs the motion of the cilia can predispose the lungs to respiratory infections. After a single exposure of the cells to e-cigarette liquid or aerosol containing cinnamaldehyde, “the cilia motion came to a complete stop,” Dr. Jaspers said.