Are mice-related vape studies highly misleading?
Vape studies on mice that has been linked to respiratory issues in humans has been met with great controversy.
The Independent reports on the vaping study on mice: “Vaping e-cigarette liquids with certain ingredients can cause cardiac arrhythmias that could increase the risk of heart attacks, a new study has suggested.”
One of the vape studies in question, titled “E-cigarettes and their lone constituents induce cardiac arrhythmia and conduction defects in mice,” was published in Nature Communications on 25th October 2022, and the validity of the research has been greatly questioned.
The researchers used mouse-specific electrocardiograms (ECGs) to measure the mice’s heart activity following acute inhalation of vapour from an e-cigarette. The researchers found that: “…chemical constituents of e-cigarettes could contribute to cardiac risk by provoking pro-arrhythmic changes and stimulating autonomic reflexes.”
Yet experts in the field of tobacco harm reduction and vaping research were swift to comment.
What do experts say about the mice vape studies findings?
Professor Jacob George, Chair of Cardiovascular Medicine and Therapeutics at University of Dundee Medical School, said: “The metabolism of mice is very different from humans and any extrapolation to overall, long-term human health is, frankly, guesswork at best.
“If this was indeed true, given the significant numbers of vapers worldwide, we would have expected to see an explosion in cardiac arrhythmia cases which we are not seeing in clinical practice, at all.
“The science is preliminary, the extrapolation is speculative and the relevance to human health, including around the nicotine effects on blood vessels, is highly questionable.”
Well said, doc.
“The science is preliminary, the extrapolation is speculative and the relevance to human health […] is highly questionable.”
Professor Jacob George
Consider the size and beat of a mouse’s heart compared to a human’s. A mouse’s heart is, on average, between 5mm to 8mm long, and beats an average of 400 to 650 times per minute. In contrast, a human’s heart is roughly the size of a fist—an average of 12cm long, beating anywhere from 60 to 100 times per minute at rest.
In truth, a mouse’s heart, metabolism, and anatomy are simply not comparable to a human.
Continuing on, Prof. Jacob George iterates, “Large human observational studies in nicotine replacement therapy users have shown that they do not increase cardiac event rates. The results of this study should not put off anyone wishing to quit tobacco smoking from trying e-cigarettes or nicotine replacement therapy.”
But what do other experts have to say?
Professor Peter Hajek, Director of the Tobacco Dependence Research Unit, Queen Mary University of London, makes an interesting note about the chemicals used in the study.
“In this study,” he says, “mice were exposed to aerosol from e-cigarette solvents with […] acrolein, a chemical that can arise from overheated e-liquid. The exposures were accompanied by short-term changes in mice electrocardiograms and increased heart rate.”
He continues, “There are several problems with generalising the findings to humans. Vapers are not exposed to any significant levels of acrolein because overheated e-liquid has an unpleasant taste and so this is avoided.”
This is something that we’ve seen in other studies: exposure to a toxicant that only arises from a burnt coil or from improperly used hardware. As we know, this taste is wildly unpleasant, and vapers know to stop using the vape when this taste occurs. In this study, and many others, researchers expose the subjects to higher levels of this chemical, which does not reflect real-world human usage.
Continuing on, Professor Hajek says, “The study used exposure levels of the other chemicals that are tolerated by humans, but the same doses can be distressing to much smaller mammals with much more sensitive sense of smell and very different tolerance of drug effects. It would be odd if animals exposed to aversive stimulation did not show a cardiovascular response!”
Lastly, Professor Hajek adds, “The reason for conducting the study in mice is unclear. Animal models are used when the experiment cannot be conducted in humans, but there are no barriers to comparing heart rate and ECG responses to e-cigarette components and to smoking in humans.”
What did we learn from the mice study?
Quite aptly, Dr Adam Jacobs, Senior Director of Biostatistics at Premier Research, says: “This paper shows that mice exposed to e-cigarette aerosol in enclosed spaces for 90 minutes experienced short-term changes in cardiac rhythm.
“Although the long-term effects of these changes are not known, it seems prudent that owners of pet mice should not allow their mice to use e-cigarettes.”
“[I]t seems prudent that owners of pet mice should not allow their mice to use e-cigarettes.”
Dr Adam Jacobs
It is extremely unlikely that the results of vape studies such as these can be effectively translated to humans, from the conditions of the study to the subjects used and beyond.
Maybe it’s just because I personally love mice—I’ve had many pet mice in my lifetime—but maybe we should leave the mice alone when it comes to vape research and focus on human trials.
E-cigarette vapor linked to cancer in mice
A study published in 2019 and funded by the National Cancer Institute (NCI) also used mice in researching as to whether e-cigarette vapor is dangerous.
A group of 40 mice was exposed to e-cigarette vapor containing nicotine for 4 hours a day, 5 days a week, over the course of a year. A control group of 18 mice was exposed to e-cigarette vapor without nicotine, while a third group of 18 mice breathed only filtered air.
In the nicotine-exposed group, 9 out of 40 mice (22.5%) developed one or more visible lung tumours. In comparison, only one mouse in the control groups developed lung cancer.
However the researchers did caution that these results do not definitively indicate how e-cigarette vapor affects the human body. The study had several limitations, including a relatively small number of mice, which are naturally prone to developing lung cancer. Nevertheless, the findings suggest the need for further study.
Summary
Vape studies using mice do highlight the need for more research into e-cigarette vapour. This seems to be the only definitive conclusion that these studies come to. Research such as this cannot be referenced as definitive proof that vapes cause cancer, or any other disease in humans due to their significant limitations.
While the vape studies themselves are only harmful to mice, their results make good headlines for news agencies. This creates misinformation surrounding vaping and potentially deters those who may be helped by vapes, such as smokers or ex smokers looking to quit.
Vape misinformation exists in lots of forms in the UK media. Check out our other article: 2 Misinformed “Popcorn Lung” News Articles Attack Vaping in the UK.
Sources:
- Independent: Vaping e-liquids can disrupt heart’s rhythm, ‘highly concerning’ study suggests – https://www.independent.co.uk/independentpremium/uk-news/ecigarettes-heart-beat-rhythm-vaping-b2210247.html
- Nature Communications: E-cigarettes and their lone constituents induce cardiac arrhythmia and conduction defects in mice – https://www.nature.com/articles/s41467-022-33203-1
- Science Media Centre: expert reaction to study of the effects of e-cigarette vapour on mice – https://www.sciencemediacentre.org/expert-reaction-to-study-of-the-effects-of-e-cigarette-vapour-on-mice/
