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The first cross-sectional study, which was designed to compare the metabolite levels of nicotine, carcinogens and toxins in five different groups, was published online in the Annals of Internal Medicine this month. The five groups included smokers who smoked cigarettes only (referred to as combustible cigarette–only), former smokers who had used either e-cigarettes or nicotine replacement therapy (NRT) for at least six months, and those who continued to smoke but who also used either e-cigarettes or NRT (dual users). All groups included 36 participants, with the exception of the smoking-only group, which included 37 individuals. The type of e-cigarette (liquids or aerosols) varied among those who used them.

The researchers analyzed urine and saliva samples for biomarkers of nicotine: Tobacco-specific N-nitrosamines (TSNAs), including the established carcinogen NNAL and a number of different metabolites of volatile organic compounds (VOCs). Both TSNAs and VOCs are well known to contribute to cigarette-related carcinogenic risk as well as cardiovascular and pulmonary diseases. The NRT-only and e-cigarette-only users had markedly lower NNAL levels than combustible cigarette-only, dual combustible cigarette-NRT, and dual combustible cigarette/e-cigarette users (P < 0.001). Former smokers who only used e-cigarettes had 97 per cent lower NNAL levels compared with those detected in smokers.

Former smokers who used e-cigarettes exclusively had the lowest levels of major urinary VOC metabolites, followed by NRT-only users, who had the second lowest levels out of the five groups analyzed (P < .001). Dual combustible cigarette-NRT, dual combustible cigarette/e-cigarette and combustible cigarette-only users all had very similar urinary VOC metabolite levels

Take home message

This study would suggest that former smokers who use e-cigarettes exclusively are not exposed to greater levels of carcinogens or toxins than those who only use NRT, which suggests that e-cigarettes may be comparable to NRT in terms of long-term safety, but not the dual use of NRTs or e-cigarettes with combustible cigarettes.