(Reuters Health) - E-cigarette liquids sweetened with flavorings like vanilla and cinnamon may harm the lungs even when they don’t contain nicotine, a U.S. study suggests.

Researchers examined what happened to monocytes, a type of white blood cell, upon exposure to flavoring chemicals used in popular e-cigarette liquids. None of the liquids contained nicotine, but the flavoring chemicals still appeared to increase biomarkers for inflammation and tissue damage, and many of them also caused cells to die.

Over time, this type of cell damage can lead to wide range of lung problems including fibrosis, chronic obstructive pulmonary disorder, and asthma, said senior study author Irfan Rahman, an environmental health researcher at the University of Rochester Medical Center in upstate New York.

“Nicotine-free e-liquids have generally been considered safe; however, the impact of flavoring chemicals, especially on immune cells, has not been widely researched,” Rahman said by email. “This study shows that even though flavoring compounds are considered safe for ingestion, it is not safe for inhalation.”

Big U.S. tobacco companies are all developing e-cigarettes. The battery-powered gadgets feature a glowing tip and a heating element that turns liquid nicotine and flavorings into a cloud of vapor that users inhale.

Even when e-liquids don’t contain nicotine, the lungs are still exposed to flavoring chemicals when the e-liquids are heated and the vapors are inhaled. Since the flavoring chemicals are considered safe to eat, e-cigarettes are often promoted as a alternative to traditional cigarettes, researchers note in Frontiers in Physiology.

When researchers exposed human lung cells to e-liquids in the laboratory, the cells increased their output of inflammation-related chemicals that can eventually lead to damage in the lungs.

Exposing cells to mixtures containing a variety of flavors appeared to cause a worse reaction than using a single flavor, the study found.

Among the single flavors, cinnamon and vanilla appeared the most toxic to the lung cells.

One limitation of the study is that the experiment didn’t involve people actually vaping and breathing in the e-liquids, the authors note. The study also doesn’t offer a complete picture of e-cigarette safety or address the potential for health problems to emerge after long-term use.

While more research is needed to better understand what happens to lung cells when people smoke e-cigarettes, the results suggest that e-liquids should be regulated and clearly labeled to list the mix of flavors used, the researchers conclude.

“It is expected that more complex mixtures or exposure at higher doses will have more adverse effects on isolated cells in the laboratory,” said Dr. Konstantinos Farsalinos, a researcher at the University of Patras-Greece and the National School of Public Health-Greece who wasn’t involved in the study.

While evidence to date suggests that e-cigarettes may be less harmful than smoking traditional cigarettes, it still make sense for users to pay attention to what’s in the e-liquids they’re inhaling, Farsalinos said by email.

“Whether pre-mixed or do-it-yourself liquids, it is the amount of flavorings that would determine the level of potential adverse effects,” Farsalinos added. “I expect simpler mixtures to be safer compared to more complex blends.”

SOURCE: bit.ly/2Bkvc7p Frontiers in Physiology, online January 11, 2018.