A new study verifies the lower risk-potential of e-cigarettes but identifies an avoidable risk


A new study was published today in the journal Nicotine and Tobacco Research, evaluating the presence of two inhalation toxins (diacetyl and acetyl propionyl) in e-cigarette liquids. Researchers, led by Dr Konstantinos Farsalinos from the Onassis Cardiac Surgery Center in Athens-Greece, obtained 159 e-liquid samples (all sweet-flavoured) from 36 manufactures and 7 countries (6 European and the US). They tested them for the presence of diacetyl and acetyl propionyl. These two chemicals are ingredients of flavourings and, although safe for use in food, have been associated with the development of respiratory dysfunction when inhaled.

The study found that 74.2% of the samples contained either diacetyl or acetyl propionyl, with more samples containing diacetyl. The levels were on average slightly lower than currently-established safety limits (set by NIOSH), but more than 40% of the samples had higher than safety levels. Of note, the highest amount of diacetyl found was 495 times higher than safety limits, while for acetyl propionyl it was 22 times higher. Tobacco cigarettes smoke contains both compounds, at levels 100 times higher for diacetyl and 10 times higher for acetyl propionyl compared to e-cigarette average daily exposure.  

In the full text of the manuscript, the authors explain that the main problem caused by diacetyl exposure is a decline in respiratory function characterized by a decline in a spirometry parameter (FEV1). Bronchiolitis obliterans (“popcorn lung disease”) is a rare condition, even in cases of exposure to high levels of diacetyl. The cut-off level of risk calculated by NIOSH for the safety limit is for 1 in 1000 chance of suffering reduced lung function associated with lifelong diacetyl exposure, which is a very conservative estimation. However, many samples contained levels much higher than safety limits. Moreover, unlike tobacco cigarettes where these chemicals are produced during the combustion process, in e-cigarettes they are used as ingredients. Thus, this represents an avoidable risk, which should be removed.

“The study is important because it confirms the lower risk potential of e-cigarettes compared to smoking but also identifies an avoidable risk” said leading author Dr Konstantinos Farsalinos. He added: “We expect to see appropriate action taken by the e-cigarette industry to remove this small but unnecessary risk, making the products even safer than they currently are”.

It is important to emphasise that only sweet flavours were selected in this study because these are most probable to contain these chemicals. Thus, it is expected that the overall prevalence of diacetyl and acetyl propionyl in all flavour-types is lower. The authors did not suggest that any flavours should be removed from the market but recommended analytical testing of the flavourings and reformulation of those containing diacetyl and acetyl propionyl.


In conclusion, this study has contributed significantly in establishing e-cigarettes as less harmful to smoking alternatives, while the identification of a small but avoidable risk will alert the industry to resolve this issue permanently and effectively. 


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