A studie published by PNAS in october 2019 suggests that electronic cigarettes causes lung cancer and bladder cancer in mice. That sounds serious but is this research project realistic and are the conclusions drawn by de scientists legitimate? The answer is again a big No.
A few hours after publishing this scientific paper it was already debunked. Prof John Britton, Director of the UK Centre for Tobacco & Alcohol Studies and Consultant in Respiratory Medicine, University of Nottingham, said:
“This study explores the effect of exposure to nicotine ecig vapour on mice. It shows that exposure to ecig vapour with nicotine causes more cancers than fresh air, but no more than you might reasonably expect by chance.
“It also shows that e-cig vapour without nicotine causes fewer cancers than fresh air.
“The findings are based on very small numbers and need to be interpreted with extreme caution.
“The comparison between mice breathing vapour and mice breathing air is not statistically significant. There is no sample size justification and no power calculation. There is no message to the public here – I suspect these results are just noise.”
Prof Peter Hajek, Director of the Tobacco Dependence Research Unit, Queen Mary University of London (QMUL), said:
“The study has unclear relevance for human vapers.
“Rodents were exposed to what are for them huge concentrations of chemicals that bear no resemblance to human exposure from vaping. Several animals in fact died during these exposures.
“The authors assigned the effects they observed to a carcinogen NNK – but NNK has been measured before in human vapers, and it is known that exposure from vaping is either negligible or none.”
Further there are some questions to be asked according this research project, like if this was a proper blind trial? It is not clear whether the group allocation was kept secret from either the researchers administering the compounds or those assessing the histopathology. This is known to potentially lead to very biased results. But also the statistical evidence on lung carcinoma is very weak.
The researchers conducted multiple statistical tests which accumulate the chance of positive results and they did not conduct a power analysis in which the sample size is large enough to identify the result they were looking for with sufficient precision. The most important point of criticism is that mice are not humans. Mice will respond to nicotine or vapor different for a number of reasons. Also the dose of vape used on these mice and the duration is not similar to the type of use humans do.
Overall, this research project was a totally waste of time and energy. It shows nothing of importance..
resource reference: PNAS, Science Media Centre, expert reaction to study on ecig vapour and cancer in mice, Dashvapes