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SMOKING caused 86 per cent of lung cancers, 65 per cent of cancers in the mouth, throat and oesophagus and 29 per cent of pancreatic cancers, among other malignancies in the UK during 2010. A recent meta-analysis of 81 studies involving almost four million people reported that smoking increased the risk of ischaemic stroke in women and men (by 54 and 53 per cent respectively) and haemorrhagic stroke (by 63 and 22 per cent respectively).

Half of those who do not quit smoking die prematurely from their addiction but, despite these health risks, many healthcare professionals have been lukewarm if not actively hostile to the arrival of electronic cigarettes.

Smokers have far fewer qualms. According to Action on Smoking and Health (ASH), 18 per cent of smokers in Great Britain have used e-cigarettes regularly during 2014 – up from 3 per cent in 2010. The proportion of smokers who tried e-cigarettes rose from 9 to 52 per cent over the same period. Several tobacco companies, recognising the commercial opportunity, have acquired or plan to launch e-cigarettes.

More attractive

E-cigarettes are proving more attractive to many smokers than nicotine replacement therapy (NRT), says ASH, and there is “little evidence that they are being used by ‘never’ smokers”. In part, ASH suggests, their success may reflect an ecigarette’s ability to replicate “the superficial aspects of the experience of smoking”. Even placebo e-cigarettes reduce cravings, alleviate withdrawal symptoms and cut daily cigarette consumption.

Nevertheless, few studies have assessed the health effects of short term and, in particular, chronic exposure to e-cigarettes. An author from the Food and Drug Administration in the US commented that “few serious adverse events have been reported related to e-cigarette use” but the dearth of data means that “studies evaluating whether e-cigarettes are less harmful than cigarettes are inconclusive”.

For example, vapour from at least some e-cigarettes contains several carcinogens and other toxins, including formaldehyde, benzene, nitrosamines, carbon monoxide and cadmium. ASH notes that the levels are “much lower than those found in cigarettes” and would not “generally cause concern”.

Nevertheless, many e-cigarettes contain aerosolised propylene glycol and glycerol, which can irritate the mouth and throat, and trigger a dry cough. Some studies suggest that the vapour may impair respiratory function and certain e-cigarettes contain sufficient nicotine to raise concerns about non-users’ exposure. Any dangers from second-hand and third-hand exposure to the vapour “have not been thoroughly evaluated”. (Third-hand exposure refers to nicotine and other chemical residues on indoor surfaces. These residues resist normal cleaning, airing rooms, opening windows, using fans or air conditioners, or confining smoking to certain areas.)

Some commentators have also expressed concern that e-cigarettes could “become a gateway to using cigarettes, cigars and smokeless tobacco”. According to the Centers for Disease Control and Prevention in the US, e-cigarette use among high school students rose from 4.7 to 10.0 per cent between 2011 and 2012. Yet many of these adolescents might still be trying to quit or reduce the harm. ASH notes that the use of e-cigarettes among children “is almost entirely” restricted to current or ex-smokers.

Clarification needed

Numerous studies are now underway that should help clarify the long-term health risks and effectiveness of e-cigarettes as a quitting device in several different populations5. In the meantime, despite (or perhaps because of) the lack of evidence and regulation, the market for e-cigarettes will continue to grow.

In January 2014, researchers identified 466 brands of e-cigarettes and 7,764 unique flavours on English-language websites. On average, 10.5 brands and 242 new flavours reached the market each month in the 17 months to January 2014. This wide variability complicates evaluation of safety and efficacy, especially as products differ in effectiveness, nicotine delivery and content between and even within brands.

The EU Tobacco Products Directive, which comes into force in May 2016, covers e-cigarettes that deliver up to 20mg/ml of nicotine. Above that level, or if manufacturers and importers decide to opt in, the MHRA will evaluate e-cigarettes in the same way as NRT3. Hopefully, improved regulatory oversight will address some of the issues that complicate the evaluation of the role of e-cigarettes in reducing the harm caused by smoking.