The effects of long-term e-cigarette use on cancer risk are unknown. While biological samples of e-cigarette users can contain metabolites of various carcinogens and toxic compounds at levels higher than non-users, it is unknown whether they are high enough to significantly increase risk of cancer.1 Some chemicals present in e-cigarette aerosols are capable of causing DNA damage and mutagenesisi, which supports the biological plausibility that long-term exposure could increase cancer risk.2
Small amounts of formaldehyde and acetaldehyde, both established carcinogens, have been detected in e-cigarette cartridges.3 Aerosol produced from some products has also been found to contain traces of carcinogenic nitrosamines,3 and some toxic and potentially carcinogenic metals such as cadmium, nickel, lead,3, 4 chromium, manganese, and nickel.4 A study commissioned by the US Food and Drug Administration in 2009 also detected carcinogens diethylene glycol and nitrosamines at very low levels.5 One review suggests that as propylene glycol in e-liquid is heated and aerosolised, it can be converted to propylene oxide, which is considered possibly carcinogenic to humans.6 A small study of never-smokers who had never used e-cigarettes found that one session of vaping altered activity of the tumour protein p53, which is important in preventing the development of cigarette-induced lung cancer.7
Compared with tobacco smoke, e-cigarette emissions tend to have lower concentrations of carcinogens;3, 8 however the presence of metals in particular may disproportionately increase the cancer risk of e-cigarettes.8, 9 Some studies have suggested that newer products with higher voltage capabilities might produce the same or even higher levels of carcinogenic formaldehyde than tobacco smoke,10, 11 but their findings have been challenged.12, 13 An analysis of e-cigarette emissions concluded that highly carcinogenic emissions are avoidable, and are largely due to device settings, e-liquid formulation, and vaping behaviour, highlighting the need for consumer education on reducing risk.8
In terms of nicotine exposure, the US Surgeon General’s most recent report concluded that there is insufficient data to conclude that nicotine causes or contributes to cancer.14 However, the International Agency for Research on Cancer Advisory Group has recommended that nicotine’s potential as a carcinogen be reassessed as a matter of high priority, because of increased population exposure to nicotine from e-cigarettes, and recent mechanistic data that ‘suggest an association with DNA damage and other pathways of carcinogenesis.’15
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References
1. Byrne S, Brindal E, Williams G, Anastasiou K, Tonkin A, et al. E-cigarettes, smoking and health. A Literature Review Update. CSIRO, Australia, 2018. Available from: https://researchnow.flinders.edu.au/en/publications/e-cigarettes-smoking-and-health-a-literature-review-update.
2. National Academies of Sciences Engineering and Medicine. Public health consequences of e-cigarettes. The National Academies Press, Washington, DC 2018. Available from: http://nationalacademies.org/hmd/Reports/2018/public-health-consequences-of-e-cigarettes.aspx.
3. Goniewicz M, Knysak J, Gawron M, Kosmider L, Sobczak A, et al. Levels of selected carcinogens and toxicants in vapour from electronic cigarettes. Tobacco Control, 2014; 23(2):133–9. Available from: http://tobaccocontrol.bmj.com/content/early/2013/03/05/tobaccocontrol-2012-050859
4. Hess CA, Olmedo P, Navas-Acien A, Goessler W, Cohen JE, et al. E-cigarettes as a source of toxic and potentially carcinogenic metals. Environmental Research, 2017; 152:221–5. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27810679
5. US Food and Drug Administration (FDA). Evaluation of e-cigarettes (DPATR-FY-09-23), 2009. Available from: http://www.fda.gov/downloads/Drugs/SCienceResearch/UCM173250.pdf
6. Kim KH, Kabir E, and Jahan SA. Review of electronic cigarettes as tobacco cigarette substitutes: their potential human health impact. Journal of environmental science and health. Part C, Environmental carcinogenesis & ecotoxicology reviews, 2016; 34(4):262–75. Available from: http://www.ncbi.nlm.nih.gov/pubmed/27635466
7. Staudt MR, Salit J, Kaner RJ, Hollmann C, and Crystal RG. Altered lung biology of healthy never smokers following acute inhalation of E-cigarettes. Respiratory Research, 2018; 19(1):78. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29754582
8. Stephens WE. Comparing the cancer potencies of emissions from vapourised nicotine products including e-cigarettes with those of tobacco smoke. Tobacco Control, 2018; 27(1):10–7. Available from: http://tobaccocontrol.bmj.com/content/tobaccocontrol/27/1/10.full.pdf
9. Gaur S and Agnihotri R. Health effects of trace metals in electronic cigarette aerosols-a systematic review. Biological Trace Element Research, 2018. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29974385
10. Jensen RP, Luo W, Pankow JF, Strongin RM, and Peyton DH. Hidden formaldehyde in e-cigarette aerosols. New England Journal of Medicine, 2015; 372(4):392–4. Available from: http://www.ncbi.nlm.nih.gov/pubmed/25607446
11. Kosmider L, Sobczak A, Fik M, Knysak J, Zaciera M, et al. Carbonyl compounds in electronic cigarette vapors: effects of nicotine solvent and battery output voltage. Nicotine & Tobacco Research, 2014; 16(10):1319–26. Available from: http://www.ncbi.nlm.nih.gov/pubmed/24832759
12. Bates C. Spreading fear and confusion with misleading formaldehyde studies. 2015. Available from: http://www.clivebates.com/?p=2706
13. Farsalinos K. The deception of measuring formaldehyde in e-cigarette aerosol: the difference between laboratory measurements and true exposure. E-cigarette Research, 2015. Available from: http://www.ecigarette-research.org/research/index.php/whats-new/whatsnew-2015/191-form-nejm
14. U.S. Department of Health and Human Services. The Health Consequences of Smoking: 50 Years of Progress. A Report of the Surgeon General. Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2014. Available from: http://www.surgeongeneral.gov/library/reports/50-years-of-progress/full-report.pdf.
15. Straif K, Loomis D, Guyton K, Grosse Y, Lauby-Secretan B, et al. Future priorities for the IARC Monographs. The Lancet Oncology; 15(7):683–4. Available from: http://dx.doi.org/10.1016/S1470-2045(14)70168-8