Early evidence suggests that e-cigarettes help smokers interested in quitting to stop or cut down, a systematic review has found.

The researchers searched Medline, PsycINFO, Cochrane Methodology Register, Health Technology Assessment and NHS economic evaluation database, Google Scholar, EMBASE and CINAHL up to February 2014. They found 81 papers they deemed relevant as they presented original data and provided evidence that could guide regulatory decisions.

The use of e-cigarettes had increased rapidly over the past five years. In the UK, use in smokers increased from 2.7% in 2010 to 6.7% in 2012 and 11% in 2013. In the US general population, use increased from 0.6% in 2009 to 2.7% in 2010 and 6.2% in 2011. E-cigarette users tended to be younger, more educated and have higher incomes than non-users.

There has been speculation that e-cigarette use will spread to non-smokers who want to experiment with nicotine use without the dangers of smoking. The reviewers found that e-cigarette ever use in non-smokers ranged from 0.1 to 3.8% (median 0.5%), and use within the past 30 days from 0 to 2.2% (median 0.3%). Smokers consistently reported that e-cigarettes helped them to quit (42-99%) or to cut down (60-80%).

E-cigarettes, are designed to deliver a nicotine dose by inhalation from a cigarette-like device, but without the other harmful ingredients of tobacco smoke. They are made using nicotine containing e-liquids. For the major e-liquid brands the labelling of nicotine content was accurate and consistent, though the authors comment that the practical features of the actual device, including the size of the battery, the nature of the heating element,

the ventilation holes and individual inhalation characteristics all have a substantial influence on the nicotine levels actually delivered.

Other contents of the aerosols included some toxicants, though in much lower concentrations than tobacco smoke, and some ingredients such as propylene glycol that have been implicated in other environments in reducing lung function and exacerbating rhinitis and asthma.

No long-term study has investigated passive inhalation associated with e-cigarettes, but the authors conclude that the risk is likely to be much lower than that associated with tobacco smoking.

Several small studies and case studies have suggested that e-cigarettes reduce the urge to smoke and that their use facilitates both reducing and quitting smoking in smokers interested in stopping.

In England, the growth of e-cigarette use has been accompanied by an increase in smoking cessation rates and no increase in smoking uptake. The devices are most frequently used by dependent smokers who want to reduce their risks.

The authors conclude by saying that regulatory verdicts on e-cigarettes and advice given by health professionals regarding their use need to follow the evidence base.

Dr Jez Thompson