February 1, 2017

expert reaction to e-cigarettes and cardiovascular risk

Researchers publishing in JAMA cardiology compared heart rate variability and markers of oxidative stress between e-cigarette users and non-users.

Prof. Paul Aveyard, Professor of Behavioural Medicine at the University of Oxford, said:

“In this study, the authors compared 16 e-cigarette users with 18 non-users and compared the two groups for heart rate variability and markers of oxidative stress.  Heart rate variability is normal and healthy, but activation of the adrenaline system in our bodies can decrease this and this may be linked with heart disease.  On two of the four measures of heart rate variability, there were no differences between the e-cigarette users and the non-users and on two measures, the groups differed.

“Oxidative stress is probably one of the main ways that cigarettes cause heart disease.  It is an important part of why cigarettes block our arteries.  In four of five measures of oxidative stress, there was no evidence of difference between e-cigarette users and non-users, while e-cigarette users had higher oxidative stress on one measure.  However, the heavier the user, the greater level of oxidative stress seen.

“The question is why these differences are occurring.  One explanation is that this is a small study.  Whenever you test several measures, as they did in this study, the greater the chance you find differences that are not real, they are simply down to chance.  It’s possible to correct for this kind of problem, but the authors did not do this.  Another possible explanation is down to psychological factors.  Most people who were using e-cigarettes had smoked in the past, while the large majority of the non-users of e-cigarettes had never smoked.  People with some psychological disorders or who are stressed show reduced heart rate variability.  On average, people who smoke or who have smoked have a higher rate of stress or psychological disorders than people who have not, so this could explain the findings on heart rate variability but not the single finding in oxidative stress.  Overall, then, this is a small study with several possible explanations for the findings, only one of which could be that using e-cigarettes is a possible risk for heart disease.

“It is important to put these results in context.  In this study, most people who were using e-cigarettes had smoked in the past.  Nearly everyone using e-cigarettes in Britain either smokes currently or has smoked, and people who are continuing to use e-cigarettes say that they do so to prevent them going back to smoking.  We know without any doubt that smoking is a major cause of heart disease and we still don’t know whether e-cigarettes pose a small risk or no risk, but we do know they are much less risky than smoking.  If a person cannot stop smoking in other ways, public health advice is to switch to e-cigarettes either partially or wholly.  This small study does not change that advice.  Compared with smoking, e-cigarettes are a better option.”

Prof. Linda Bauld, Professor of Health Policy at the University of Stirling, said:

“It is important to assess the cardiovascular effects of e-cigarette use as we know that tobacco smoking is the main preventable cause of heart disease, and e-cigarettes provide an alternative to tobacco. This study looks at the short term effects of vaping on markers of increased risk of cardiovascular disease (CVD) amongst people not currently smoking. It concludes that vaping might be associated with increased risk. However, these findings cannot conclude that heart disease will develop as a result of vaping without smoking. In order to develop our understanding of whether vaping causes any potential pathophysiological effects, further mechanistic research is required.

“A number of questions arise from looking at the study. First, the measures used are mainly applied to people who have already had a cardiac event rather than healthy young volunteers, which may pose challenges for interpretation. Secondly, sensitivity or specificity for nicotine effects is not adequately discussed in the paper. Nicotine is known to stimulate the sympathetic system, but nicotine replacement therapy is considered safe and is approved even for long term use by smokers (including those with cardio-vascular disease) and this is not made clear.  Finally, there is no direct comparison in the study between the risks of tobacco smoking to cardiovascular health and to vaping. This is particularly relevant because, for example, the response of vapers to controlled breathing was found to be normal in this study, unlike the response observed in smokers in other studies. These comparisons are important when communicating any risks or benefits of e-cigarette use.

“However, the questions posed in this study do merit research with longer term follow up particularly for CVD researchers who specialise in arrhythmias – irregular heartbeat. In the meantime, this study should not be used to suggest that vaping is as dangerous as smoking, for CVD or any other conditions. This study does not provide this evidence, and does not prove that vaping causes heart disease.”

* ‘Increased Cardiac Sympathetic Activity and Oxidative Stress in Habitual Electronic Cigarette Users’ by Roya Moheimani et al published in JAMA Cardiology on Wednesday 1 February.

Declared interests

Prof. Linda Bauld: None to declare

Prof. Paul Aveyard: “Paul Aveyard has no personal financial connections to e-cigarette or pharmaceutical companies but in one study on smoking cessation, Glaxo Smith Kline is supporting the study by donating nicotine patches to the NHS.”