A study from the University of Hawaii at Manoa found high concentrations of menthol in electronic cigarettes are likely harmful to the lung’s ability to function.

UH researchers found that flavorings used in e-cigarettes — menthol, in particular — impair a vital lipid-protein film that lines the alveoli, or tiny air sacs, in the lungs. This film, called the lung surfactant, is essential to one’s ability to breathe.

The findings, recently published in the “American Journal of Physiology — Lung Cellular and Molecular Physiology,” come as vaping among youth in Hawaii and across the nation is rising, and as governments examine regulations in the tobacco industry.

The study’s author, Yi Zuo, UH professor of mechanical engineering and adjunct professor of pediatrics, said the findings are the culmination of research that started four years ago — and were surprising for the team.

“E-cigarettes were initially advertised as a healthier and safer alternative to conventional tobacco smoking when they first appeared in the mid-2000s,” Zuo wrote in the study’s introduction. “However, increasing research evidence, especially long-term (more than 10 years) toxicological data that emerged only in recent years, has suggested that e-cigarettes are not as safe as originally promised.”

In 2018, Zuo, noting the popularity of vaping among youth, embarked on an investigation into how inhaled aerosols affect the lungs.

Studies already show the use of e-cigarettes has been linked to asthma and other chronic lung diseases in adolescents.

Zuo and his team decided to take a closer look at all of the components of an e-cigarette, including the combination of chemicals used to make flavorings such as strawberry or bubble gum, as well as nicotine, and their impact specifically on the lung surfactant.

Given that there are more than 15,000 vaping flavor blends, the team looked at the top 20 flavoring chemicals initially, then narrowed them down to three for the study: menthol, ethyl maltol and ethyl butyrate.

Using various research techniques, they examined the impacts of these chemicals on the biophysical processes of animal- derived surfactant samples. They also collaborated with UH chemistry professors to analyze how menthol molecules interact with phospholipids, a major component of the cell membrane.

“We drew the conclusion that menthol among all three flavors we studied — also in comparison to nicotine — is perhaps the most damaging component,” Zuo said. “We found whenever the e-liquid contains menthol, it does the most damage to the lung surfactant.”

This is relevant, given that e-cigarette use, or vaping, is on the rise among Hawaii’s youth, with menthol as one of the most popular flavorings.

Menthol is a substance found in peppermint, spearmint and other mint plants and has long been considered safe, the study noted.

It is popular in cough drops, gum and candy because of its soothing sensation. It is also used in topical applications such as ointments to relieve minor pain and irritation.

However, the route of delivery is important, Zuo said, and its impacts are different when smoked or inhaled. Additionally, the concentration of menthol is important, and the team found it to be high in e- cigarette products.

“This menthol in traditional cigarettes is very low compared to what’s used in e-cigarettes,” he said. ” We’re talking about an order of magnitude higher.”

Zuo said the concentration of menthol in cigarettes, for example, is at about 5 milligrams per milliliter, while it can be 10 times higher or more in e-cigarettes.

“People think menthol is safe but apparently they’re not as safe as when you use it externally, if you inhale it into your lungs at high concentrations,” Zuo said. “That can be very damaging.”

Menthol also has been a point of contention between federal regulators, the tobacco industry and health advocates.

It is the only cigarette flavor not prohibited under the 2009 Tobacco Control Act, but health advocates cite it as the reason youth get started with and eventually get hooked on smoking.

Menthol creates a cooling sensation in the throat and masks the harsh flavors of tobacco, they said, to appeal to first-time smokers, and should also be prohibited.

The U.S. Centers for Disease Control and Prevention said menthol enhances the effects of nicotine on the brain, and can make tobacco products even more addictive.

The Coalition for a Tobacco-Free Hawaii continues to push for bills banning all flavored tobacco products, including menthol, on store shelves statewide.

According to the coalition, 1 out of every 5 students in middle school, and 1 out of every 3 students in high school report using e-cigarettes regularly, with rates even higher on neighbor isles. Most said they started tobacco use with flavored products.

Additionally, 78% of Native Hawaiian and Pacific Islander smokers in Hawaii use menthol cigarettes.

The U.S. Food and Drug Administration in April released its long-awaited plan to ban menthol cigarettes and flavored cigars, a year after announcing it, due to their toll on youth and Black smokers. The ban is not yet in effect, and does not include e-cigarettes.

Health advocates are concerned that when the ban goes into effect, many smokers will shift to menthol e-cigarettes.

Zuo hopes the research findings will offer a better understanding of the health impacts of e-cigarettes to help inform regulations.

The research was a collaborative effort between Zuo’s lab and professors Ellinor Haglund and Rui Sun in the UH-Manoa Department of Chemistry. It was supported by a National Science Foundation award, George F. Straub Trust and Robert C. Perry Fund of the Hawaii Community Foundation.

Zuo said the study is the first of a series, and his team intends to analyze other popular chemical flavorings and further investigate the effects of e-cigarettes.