E-cigarettes an evidence update A report commissioned by Public Health England

E-cigarettes: an evidence updateAlthough e-liquid can be heated to a temperature which leads to a release of aldehydes,the resulting aerosol is aversive to vapers and so poses no health risk.SummaryThere is no indication that EC users are exposed to dangerous levels of aldehydes.Effects of e-cigarette vapour on mice lungsA paper published in February 2015 [135] generated worldwide media coverage withclaims that it linked EC to lung inflammation, lung infection, and even lung cancer.Groups of mice were put in a small container exposing them to vapour from six EC(‘Menthol Bold’ 1.8% nicotine) puffed on a rotating wheel at six puffs per minute for 1.5hours, twice daily, over two weeks. The control mice were not exposed to this treatment.Animals were infected with either streptococcus pneumonia via intranasal instillationand killed 24 hours later, or with tissue culture influenza virus and monitored for weightloss, mortality, and lung and airways inflammation. Compared to the control group, theexperimental animals had an increase in pro-inflammatory cytokines, diminished lungglutathione levels, higher viral titre, and were more likely to lose weight and die. Thestudy identified free radicals in EC vapour as the potential culprit.There are several problems with the study and with the way its results have beeninterpreted.EC vapour is inhaled as a replacement for tobacco smoke, but the study attempted nocomparison of the effects on the lungs from smoke and vapour exposures. This makesa meaningful interpretation of the results difficult. A comparison was made, however, ofthe levels of free radicals. Even at the very high vapour density generated by the studyprocedure, the level of free radicals identified in vapour was “several orders ofmagnitude lower than in cigarette smoke”.In addition to this, the mice in the experimental group were exposed to a much higherlevel of stress than the control group, and stress affects bacterial and viral response.Long and repeated containment in the small and crowded smoke chamber emitting anoverpowering smell is a stressor in itself, but the animals also suffered repeated nicotinepoisoning. The mice showed an average cotinine concentration of 267ng/ml. Cotinine isthe primary metabolite of nicotine and in humans the amount of nicotine needed to givesimilar cotinine levels are tolerated by heavy smokers, but highly aversive to nonsmokers,who would be expected to feel sick and vomit at this level of exposure. Miceare much more sensitive to nicotine than humans (LD50 in mice is 3mg/kg, in humans78