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Use of electronic cigarettes with added menthol flavoring increased the number of inhaled particles and was associated with worse lung function in current or former combustion cigarette smokers, according to a study that used a specially designed robotic system that mimics the mechanics of breathing.

Compared with e-cigarettes with liquids that were not flavored with menthol, menthol-flavored products produced a significantly higher level of 1-10 µm particles when inhaled, reported Kambez H. Benam, DPhil, of the University of Pittsburgh, and co-authors.

In a retrospective analysis of data from the COPDGene cohort, menthol product users had an average 0.06 lower forced expiratory volume in the first second to the forced vital capacity of the lungs (FEV1/FVC) when compared with those who used other flavors (95% CI -0.01 to -0.12, P=0.01), they said in .

The addition of menthol flavor to the liquid base in e-cigarettes, measured as propylene glycol (PG) to vegetable glycerin (VG), led to increased particle counts across all particle size ranges (300 nm to 10 µm) even at a 0.01% dosage. When Benam and team compared popular product Vuse Alto Menthol with its non-menthol counterpart, Vuse Alto Golden Tobacco, they found that Vuse Alto Menthol produced larger amounts of 1-2.5 μm, 2.5-4 μm, and 4-10 μm particles when aerosolized.

Menthol remains a popular option among those who vape, particularly younger users. As of October 2022, . reported use of e-cigarettes in the previous 30 days, with 85% using flavored products.

One NIH study among adolescent and young adult users of flavored e-cigarettes found that the largest group (34%) . Menthol and other cooling flavors have only increased in popularity over the years, from .

"Menthol is a substance naturally found in mint plants (and is added to some food/beverages), so some may assume it would be fine to inhale it," Benam told MedPage Today. "Just because something is or considered safe orally, does not mean it would be safe if inhaled."

"For a middle/high schooler who has not smoked combustion cigarettes in the past and thinks it is cool to try a menthol-flavored vaping product, they should know that not only are they exposing their lungs to irritants and toxins in e-cigarette aerosols, but they are getting more particles into their lungs, just because of the menthol," he added.

In their paper, the authors noted that an increase in the number of particles from the added menthol flavoring will increase aerosols -- known to contain many harmful substances such as nicotine and multi-functional carbonyls, including formaldehyde -- delivered to the lungs.

"A number of in vitro and in vivo studies suggest that EC [electronic cigarette] aerosols can provoke lung inflammation, oxidative stress, DNA damage, airway hyperresponsiveness, induce epithelial-to-mesenchymal transition, impact cellular viability, and impair lung function and anti-pathogen immune responses," they wrote.

According to an accompanying , the researchers developed a "vaping robot," the Human Vaping Mimetic Real-Time Particle Analyzer (HUMITIPAA) to improve preclinical testing on how mixing vaping liquids and adding flavorings affects vapor composition and its health effects. By mimicking the temperature, humidity, puff volume, and duration, this robotic system can simulate the pattern of healthy and diseased breathing and reliably predict lung toxicity related to e-cigarettes.

The COPDGene cohort included 94 participants, 69 of whom used other flavored e-cigarette products and 25 who used menthol products. Mean age was 65.2, 55.3% were women, 67% were Caucasian, and 33% were African American.

At 5- and 10-year follow-up, participants completed questionnaires on e-cigarette usage, including detailed questions on the duration and use of various products and flavorings. They also underwent post-bronchodilator spirometry tests and CT scans.

There are limitations to the study, Benam and colleagues said. For example, particles measuring less than 300 nm weren't analyzed. In addition, the sample size for the retrospective analysis was small, and the authors said they hope to repeat the analysis with a larger sample size soon.

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