E-cigarette users may be exposed to fewer carcinogens, toxins than smokers, study finds

Former tobacco smokers who switched to electronic cigarettes or nicotine replacement therapy (NRT) had lower levels of tobacco-related carcinogens and toxins than current smokers in a recent cross-sectional study.

Researchers in London measured and compared the biomarker levels of 181 participants in five groups: long-term (six or more months) tobacco smokers (five or more cigarettes/day), former smokers with long-term e-cigarette-only or NRT-only use, and those with long-term dual use of cigarettes and e-cigarettes or cigarettes and NRT (n=36 to 37 per group). Overall, participants were mainly male, white, and relatively young (mean age, 37.8 years) and had started smoking around age 18 on average.

Using the participants' urine and saliva samples, researchers measured differences in metabolites of nicotine, tobacco-specific N-nitrosamines (TSNAs), and volatile organic compounds (VOCs) between groups. Results were published online on Feb. 7 by Annals of Internal Medicine.

After controlling for confounders, the researchers found that nicotine intake was roughly similar between groups, but there were significant differences in metabolite levels for TSNAs and VOCs. In terms of the carcinogenic metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), the NRT-only and e-cigarette-only users had substantially lower levels than the tobacco smokers and dual users (P<0.001). Of all the groups, the e-cigarette-only users had the lowest NNAL levels, equaling a 97% reduction compared to smokers.

There were no large differences in NNAL levels between tobacco smokers and dual users of cigarettes and e-cigarettes, but dual users of cigarettes and NRT had somewhat lower NNAL levels than tobacco smokers. Results were similar yet less pronounced for the other TSNAs measured.

Of all the major VOC metabolites, e-cigarette-only and NRT-only users had significantly lower levels compared with all other groups (P<0.001). In general, e-cigarette-only users had the lowest levels of VOC metabolites, followed by NRT-only users, and there were no detectable differences between the other groups.

“… [O]ur results suggest that complete substitution of combustible cigarettes with e-cigarettes may reduce disease risk and support the assertion that e-cigarette use may be less harmful than smoking. We found no evidence that long-term e-cigarette-only use was associated with greater levels of carcinogens or toxins than NRT-only use; on some measures, e-cigarette-only use was associated with lower levels,” the study authors concluded. Limitations of the study include its cross-sectional design, self-selected sample, and lack of evaluation of different types of e-cigarettes or NRT.

In related news, a small study (n=42) found potential adverse cardiovascular effects of e-cigarettes after comparing 23 e-cigarette users with 19 nonsmoker/nonuser controls. Habitual e-cigarette use was associated with significantly increased low-density lipoprotein oxidizability and a shift in heart rate variability toward sympathetic predominance, according to results published online on Feb. 1 by JAMA Cardiology. However, because these are indirect indices of cardiovascular injury, it is unclear to what extent these changes show an increase in the risk of cardiovascular disease, and further studies are needed, an accompanying editorial noted.