The puff from e-cigarette aerosols and flavourings may damage lung cells by creating harmful free radicals and inflammation in lung tissue, according to a new study. However, critics counter that the study should have compared aerosols with cigarette smoke, not fresh air.
Researchers at the University of Rochester, US, exposed human lung cells to e-cigarette aerosols and reported signs of stress and toxicity (PLOS One, doi:10.1371/journal.pone.0116732). Lung cells showed an increased secretion of inflammatory cytokines and oxidative stress and morphological change. Mice exposed to e-cigarette vapour for five hours a day also showed signs of stress and lung inflammation.
This research shows that e-cigarettes may pose significant health risks and should be investigated further, says senior author Irfan Rahman. The heating element in e-cigs converts a liquid solution known as a juice into an aerosol containing nicotine that mimics tobacco smoke. The new research points to flavourings like cinnamon as causing inflammation.
‘Flavouring agents in particular have organic molecules like benzenes, aldehydes, pyrrole rings, and phenol ring structures and these become highly reactive and toxic in the vapour,’ says Rahman. ‘It really depends which flavouring you use. Some like cinnamon and candy flavours may be more toxic than conventional tobacco smoke even,’ he adds.
Peter Hajek at Queen Mary University, London, UK, is critical of the paper. ‘[It] provides no comparison with cigarette smoke, which is the key issue of interest. Inhaling almost anything produces lung reaction.’
He also points to another problem: ‘Stress may affect bacterial and viral response. Mice, which were put in a dense and for them strongly smelling fog, repeatedly for two weeks, must have been considerably more distressed than those left alone.’
However, toxicologist Thomas Hartung, director of the Centre for Alternatives to Animal Testing (CAAT) at Johns Hopkins University, comments that there are ‘almost 1000 times more [free radicals] generated in a normal cigarette, and it’s important to note that this is an animal study. The dosing [of nicotine] achieved in the blood was comparable to what you can achieve in humans, but at this level 20% of the animals died. It is perhaps not surprising that at this level of intoxication the animals suffer from inflammation.’
Hartung adds that, in his own view, flavourings are ‘a big problem’. He points to an estimate showing that, as of January 2014, there were 466 distinct brands of electronic nicotine products and at least 7764 unique flavours (JAMA, doi:10.1001/jama.2014.14830). The safety of inhaling these flavourings needs to be tested, he says.