A newspaper has reported on a study claiming that electronic cigarette liquid can disrupt heart rhythms, but has failed to highlight that the study was conducted on mice and involved toxic doses. An expert on tobacco reduction has pointed out that the only information this study provides is that "pet mouse owners should not allow their mice to use electronic cigarettes.
According to The Independent, a new study has found that using e-cigarette fluids containing certain ingredients can cause heart rhythm irregularities, thereby increasing the risk of heart attacks.
A recent study published in Nature Communications suggests that e-cigarettes and their individual components can cause irregular heart rhythms and conduction defects in mice. The researchers conducted electrocardiogram tests on mice after acute inhalation of e-cigarette vapors. They argue that "our findings suggest that the chemical composition of e-cigarettes may increase cardiac risk by inducing changes that promote arrhythmogenesis and stimulate autonomic reflexes.
Experts in tobacco harm reduction and e-cigarettes quickly criticized the study. Professor Jacob George, Head of Cardiovascular Medicine and Therapeutics at the University of Dundee Medical School, said: "The metabolism of mice is very different from that of humans, and to be honest, any inference to long-term human health effects are at best speculative. If this were indeed true, given the large number of e-cigarette users worldwide, we would have expected to see a dramatic increase in cases of arrhythmia, which we have not seen in clinical practice.
The controversial nature of e-cigarettes brings into question the preliminary and speculative science surrounding its potential impact on human health, including the effects of nicotine on blood vessels. However, large-scale observational studies of users of nicotine replacement therapy have shown no increase in heart events. These findings should not deter those seeking to quit smoking from attempting e-cigarettes or nicotine replacement therapy. This early-stage preclinical research requires further clinical work before it can be considered directly related to human health.
Professor Peter Hajek, director of the Tobacco Dependence Research Department at Queen Mary University of London, added that "in this study, mice were exposed to aerosols from e-cigarette solvents with and without nicotine, as well as acrolein (a chemical that may be produced due to overheating) in e-cigarette liquid. Such exposure was associated with short-term changes in the mice's electrocardiograms and an increase in heart rate.
When talking about applying the results of this study to humans, there are several issues to consider. Electronic cigarette users are unlikely to be exposed to significant levels of acrolein since overheated e-liquid produces an unpleasant taste that people tend to avoid. While the study used exposure levels to other chemicals that humans can tolerate, the same dose may cause significant pain in much smaller mammals with more sensitive olfactory systems and varying tolerances to medication. It would be strange if animals exposed to aversive stimuli did not show a cardiovascular response. The reason for using mice in this study remains unclear. When experiments cannot be conducted on humans, animal models may be used, but comparing heart rate and electrocardiograms for electronic cigarette components and human smoking reactions is not without hurdles.
Professor Kevin McConway, Honorary Professor of Applied Statistics at The Open University in the UK, continues to criticize and has released a detailed statement saying: "As a statistician and not a biologist, I am unable to comment on the physiological details of this study. However, in my view, most aspects of the statistical analysis of the experimental results are reliable, and the study provides good evidence that certain components of e-cigarettes do indeed affect some aspects of mouse heart function when the mice are exposed to these components in the way done in this study. Nevertheless, while I believe that investigating the potential harmful effects of e-cigarette components is certainly worthwhile, and I also believe that animal experiments can play a role in this work, this work cannot answer some important questions.
I don't believe any knowledgeable commentator has suggested that using e-cigarettes is without risk. The important question is how the harm of using e-cigarettes compares to the harm that would result if the person did not use them. This, of course, depends on what the person would do if they did not use e-cigarettes. If they are a traditional smoker and e-cigarettes help them quit, then using e-cigarettes would prevent greater harm from their previous smoking habit. Other studies have shown that e-cigarettes can effectively help people quit smoking and are often more effective than nicotine replacement therapy like patches or gum. So, when used by smokers, the real question is not whether e-cigarettes are completely harmless, but whether they are safer than continuing to smoke or using other methods to quit, which may be less effective. This new study does not shed light on that question, and there is no evidence in its findings to suggest that using e-cigarettes is as harmful as smoking regular cigarettes, even in mice.
For those who are not yet smokers, electronic cigarette companies say it may be different. However, people still need to consider whether using electronic cigarettes may lead to other dangerous habits, such as using different drugs.
To the best of my understanding, this study has the potential to distinguish the effects of different components in e-cigarettes to some extent, which is an advantage. For example, this could lead to the development of safer e-cigarettes. However, as noted by the researchers, the reactions to various chemicals observed in mice may not necessarily apply to humans, even though this study specifically looks at several components of e-cigarettes and their potential effects on mice. Therefore, there is still a lot of work to be done and all relevant factors must be taken into consideration.
In addition, the study used a very small number of female mice - only four - and these mice did not come into contact with most of the substances involved. This means that, as the researchers have themselves acknowledged, some of the potential conclusions about gender differences are not based on evidence. Finally, these mice were (of course) completely unfamiliar with e-cigarettes, and the researchers note that the effects may be very different for individuals who have experience with e-cigarettes or tobacco use.
Dr. Adam Jacobs, Senior Director of Biostatistics at Premier Research, provided commentary on the study, stating "This study suggests that mice exposed to e-cigarette aerosol in a closed space for 90 minutes experience short-term changes in heart rhythm. While the long-term effects of these changes are not yet clear, it seems prudent for pet owners to avoid exposing their rodents to e-cigarettes. For humans, while e-cigarettes cannot be considered completely safe, there is a significant amount of evidence showing it to be much safer than smoking combustible cigarettes. Therefore, smokers who switch from traditional cigarettes to e-cigarettes will greatly reduce their health risks.
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