Study shows menthol flavour especially harmful to vape users

Several of the chemicals used in flavoured e-cigarettes have been suspected for years of causing serious and irreversible lung damage in people who vape, and new research suggests one "vape juice" flavour is especially harmful.

Adding mint flavour to e-cigarette liquids produces more vapour particles and is associated with worse lung function in those who smoke, researchers from the University of Pittsburgh reported in a study published in the medical journal Respiratory Research on April 10.

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"Many people, especially youth, erroneously assume that vaping is safe, but even nicotine-free vaping mixtures contain many compounds that can potentially damage the lungs," said Kambez H. Benam, senior author and associate professor at the University of Pittsburgh School of Medicine, in a media release. "Just because something is safe to consume as food does not mean that it’s safe to inhale."

Using a biologically-inspired robotic system that mimics how a human inhales from a vape pen or e-cigarette, Benam and his team showed that commercially available e-cigarette liquids containing menthol generate a greater number of toxic microparticles compared to menthol-free juice.

The team also analyzed patient records from a cohort of e-cigarette smokers that revealed menthol vapers took shallower breaths and had poorer lung function compared to non-menthol smokers regardless of age, gender, race, years of smoking or whether they used nicotine or cannabis-containing vaping products.

Menthol is a flavour additive with a minty taste and aroma that the U.S. Food and Drug Administration says reduces the irritation and harshness of smoking, increasing the appeal of smoking for youth and young adults. Menthol also interacts with nicotine in the brain to enhance nicotine’s addictive effects, making it harder for people who smoke menthol cigarettes to quit smoking. For these reasons, the U.S. FDA has begun to pressure the tobacco industry to stop using menthol in products like cigarettes and cigars.

However, according to Benam and his co-authors, the vaping market is expanding too quickly for regulators to keep up with.

This is partly because traditional toxicity testing involving animals or living cells grown on a Petri dish can take months to produce high-quality, clinically-relevant data. According to the study, testing the safety of aerosolized products – otherwise known as vape pens or e-cigarettes – is further complicated because tests are usually conducted using mice and rats, despite the fact that their respiratory anatomy is so different from ours.

The vaping robot Benam and his team developed mimics the temperature, humidity and puff volume and duration of a human smoker. It can also simulate the patterns of healthy and diseased breathing and can reliably predict lung toxicity related to e-cigarettes.

The team hopes the research will show how their device can improve pre-clinical studies that look at how vaping liquids and additives combine to create different health effects. Mostly, though, they hope it demonstrates how e-cigarettes might not be the innocent alternative to cigarettes that clever marketing portrays them as.

"The main message that we want to put out there is for people, especially young adults, who haven’t smoked before," Benam said. "Switching to e-cigarettes may be a better, safer alternative for someone who is trying to quit smoking regular tobacco products. But it’s important to have full knowledge of e-cigarettes’ risks and benefits before trying them."

A GROWING BODY OF RESEARCH

Flavoured vaping products have been on the market in Canada since at least 2004 and in the U.S. since the late 1990s, and a growing body of research is shedding light on the specific ways the chemicals they contain damage lungs.

A study published by researchers from Massachusetts General Hospital in May 2022 was the first to microscopically examine the lung tissue of a small number of e-cigarette users for chronic disease. That study found fibrosis and damage in the small airways, similar to the chemical inhalation damage typically seen in soldiers returning from overseas conflicts who had inhaled mustard gas or similar types of noxious gases.

“We also observed that when patients ceased vaping, they had a partial reversal of the condition over one to four years, though not complete due to residual scarring in the lung tissue," Dr. Lida Hariri, lead author and physician investigator at Massachusetts General Hospital, said in a media release.

That study was published in the medical journal NEJM Evidence on May 13, and is one of several in recent years to raise the alarm about the damaging effects of vaping on lung tissue, blood vessels and the brain.