Professor Linda Bauld unpicks recent headlines around a study looking at the impact of e-cigarette vapour on human cells, and finds little support for the claim that they’re as harmful as smoking

Just under a year ago, I wrote a response to an article by a journalist who claimed there was no evidence that vaping is less harmful than smoking. Since then, many new studies have been published, including a Cochrane review showing their promise for aiding smoking cessation, and a comprehensive review for Public Health England that concluded, as previous reports have done, that e-cigarettes were significantly safer to users than continuing to smoke.

Yet the debate in the media rages on, fuelled in part by misleading press releases from journals and academics. The latest example involves a study published online in the journal Oral Oncology in November, but press released just this week, at a time when many smokers are making new year resolutions to stop smoking. The press release cited the lead author who concluded that ‘based on the evidence to date, I believe that [e-cigarettes] are no better than smoking regular cigarettes’.

So what did the study involve? A team who specialised in studying head and neck cancer conducted a lab study that exposed human epithelial cells (the type that line the mouth and lungs) in Petri dishes to the vapour from two brands of e-cigarettes. The cells were treated with e-cigarette extract every three days for up to eight weeks, with some of the extract containing nicotine and some being nicotine-free.

At the end of the treatment period, the cells were harvested and examined for damage using established methods. The treated cells were more likely to show DNA damage, and some of the cells died. The authors highlight in the press release that DNA strand breaks were observed, damaging the cellular repair process, and that this can ‘set the stage for cancer’. Worse damage was observed in the cells exposed to the e-liquid that contained nicotine, but the nicotine free liquid also altered the cells.

In vitro studies like this are useful for examining how certain substances can affect cell growth and repair, but they can’t show what actually happens to cells in the human body under ‘real world’ conditions. For example, one of the main constituents in electronic cigarette liquid is propylene glycol, which has been shown in In vitro studies to have toxic effects and to damage cells. Yet propylene glycol is widely used in a range of products including those we consume such as cough syrup, asthma inhalers and the ‘fog’ (sometimes called ‘dry ice’) used in theatrical productions.

Yet the key issue for this current study of e-cigarettes is not whether extensive and prolonged exposure to e-liquid vapour (of a duration and intensity that wouldn’t occur in human use) changes human cells, but rather what the e-liquid was compared to, and what this can tell us about the relative harm of tobacco smoking compared with e-cigarette use. The authors claim their study shows that e-cigarettes are no safer than tobacco, and experienced science editors in newspapers were quick to reproduce these claims without careful scrutiny of the original article.

In reality this study tells us little or nothing about the safety of e-cigarettes compared to smoking. The main results in the study compare e-liquid treated cells with completely untreated cells, and show more damage to those exposed to e-liquid vapour.

In only one small part of the article, not covered in the press release and not picked up by the media, do the authors mention that they also exposed some cells to tobacco smoke, using media from Marlboro Red filter cigarettes. Yet the authors could not directly compare the cigarette and e-cigarette treated cells, because the cigarette treated samples all died within 24 hours. Cigarette smoke was so toxic that the cells did not survive beyond this short period, whereas the e-cigarette cell lines were topped up with e-liquid every three days, and the testing continued for several weeks.

It is possible that the authors originally set out to directly compare cell response between cigarette and e-cigarette treated cells but were unable to because of the high toxicity of tobacco smoke. All they were left with was to examine the absolute (rather than relative) risk of e-liquid on cells. Indeed an alternative headline for the press release, as a colleague from a cancer charity has already pointed out, could have been ‘cells can survive for 8 weeks in e-cig liquid but only 24 hours in cigarette extract’. In other words, if we compare e-cigarette vapour with fresh air we find the presence of some toxicants, as previous research has done. But it seems from the results of this study that if we compare e-cigarettes with tobacco smoke, e-cigarettes are safer.

Few things are risk free, and no one has claimed that e-cigarettes are. However, as an alternative to a uniquely deadly product that kills one in two of its regular users, who lose on average ten years of life, e-cigarettes are a far better alternative.

Distorting study findings to say otherwise does a huge disservice to policy makers, health professionals, the general public and most importantly smokers who are looking for accurate advice about electronic cigarettes. Recent research in both the UK and USA has shown that smokers increasingly believe that these alternatives to tobacco are just as harmful as cigarettes . Studies like this one and media hype about their results contributes to this misperception. Meanwhile, tens of thousands of people suffer and die prematurely each year in the UK from cancer, heart disease and other conditions directly linked to smoking. Electronic cigarettes offer one possible escape route. Researchers and journalists need to stop blocking the exit.

Linda Bauld is Professor of Health Policy at the University of Stirling, Deputy Director of the UK Centre for Tobacco and Alcohol Studies.and holds the CRUK/BUPA Chair in Behavioural Research for Cancer Prevention at Cancer Research UK . She is a former scientific adviser on tobacco control to the UK government and chaired the NICE guidance group on tobacco harm reduction.



