1 Sep 2010

Cancer risk in humans reduced by e-cigarettes



Is the nicotine delivered via the e-cigarette going to promote cancer in already existing pre-cancerous cells?


Answer. Not likely and not in the next 10 years.


1) Nicotine is not a known carcinogen

Nicotine, inhaled or by any route, is not recognized by the state of California as a known cause of cancer in humans or animals. Hundreds of other chemicals are so recognized, and scores of them are in cigarette smoke. Second hand tobacco smoke is recognized in this way.


2) Careful follow up for 10 years - the Lung Study in the USA has followed thousands of ex-smokers for five years and then for 7.5 years after that,. Risk of cancer of the lung was increased in those who continued to smoke, but not in those using nicotine alone compared with those who quit entirely.[1] That means 10 years of follow-up. If their cells were pre-cancerous to start with, and nicotine was a cause of cancer, new cancers would have been expected to appear within those 10 years.


3) Widespread use of nicotine for 25 years. Since 1984, nicotine has been given to millions of smokers trying to quit smoking, to help them quit smoking, with no reported increase in lung cancer. Over 40,000 were followed for at least 6 months, and some have been followed for 20 years.[2] Some 8% of nicotine gum users become long term users, [3] but no increase in cancers has been reported in long term users of nicotine gum or patch.


Pre-cancerous cervical cells are commoner in smokers. Any smoker so affected, should obtain rigorous follow-up. We have no reason, however, to believe e-cigarettes will increase the risk of the cells becoming cancerous.


E-cigarette use reduces risk of cancer by supplanting the smoking of tobacco cigarettes


Using e-cigarettes INSTEAD of smoking tobacco cigarettes is bound to reduce the risks of lung cancer, because the cancer-causing gases such as 1,3 butadiene found in the smoke of all cigarette brands, are no longer inhaled.


Switching to e-cigarettes with nicotine continued, can be expected to reduce lung cancer risk the same as altogether quitting cigarettes without e-cigarettes.


Complete quitting and complete switching required

100% altogether-quitting or 100% quitting by 100% switching to e-cigarette is required.

Anyone continuing to smoke even one cigarette per day along with e-cigarettes (dual smoking) increases risk of premature death by about half.[4]





If nicotine can cause cancer in specially-bred susceptible mice, how can nicotine e-cigarettes in humans lower cancer risk?


1)    For smokers, nicotine’s danger lies in the fact that nicotine is what smokers smoke for, and the cheapest way to obtain a nicotine hit is still by smoking cigarettes. Over 98% of total inhaled nicotine in NZ is probably in cigarette smoke.

2)    Public health argument. Nicotine products including e-cigarettes used as a replacement for smoking, are expected on the basis of the known effects of their respective chemical constituents, to prevent far more cancer than they are likely to ever cause.

3)    Health risk for the user. The risk of relapse to smoking remains substantial for the first year after stopping smoking.

4)    Human rights argument. Smokers continuing to smoke past age 35 years face a 1 in 2 eventual risk of early death, and so should be entitled, in self-protection, to :

        buy e-cigarettes for recreational use without the need to quit nicotine

        use e-cigarettes for so long as they feel the need, to avoid risk of relapsing to smoking. On this point, the smoker is likely to be the best judge, as most doctors have never smoked.


In e-cigarettes, the nicotine inhaled per puff is much less than (about one tenth) in a cigarette puff, and risk of cancer in mice from nicotine in their diet is of great theoretical interest for researchers, but no proven effect for humans.


Cancer risk has been studied in a million Americans, and on follow-up the lung cancer rates were 10-20 times higher for cigarette smokers, compared with never-smokers.

E-cigarettes protect from cancer to the extent that e-cigarette users no longer smoke tobacco cigarettes.


Cancer risk in predisposed mice

The billions of free oxygen radicals and numerous known cancer causing gases in every cigarette smoke puff, substances in smoke besides nicotine, not to mention the solids in the tar, are the cause of increased cancer risk in smokers.

However, in test-tube cancer cell lines and mouse models nicotine itself is known to increase blood supply of some cancers, and may directly stimulate growth of some cancer cells and increase malignancy [5,6] So far this applies to breast and lung cancer in mice.


1.     Murray RP, Connett JE, Zapawa LM. Does nicotine replacement therapy cause cancer? Evidence from the Lung Health Study. Nicotine Tob Res. 2009 Sep;11(9):1076-82. Epub 2009 Jul 1.

2.     Stead LF, Perera R, Bullen C, Mant D, Lancaster T. Nicotine replacement therapy for Smoking Cessation. Cochrane Database Syst Rev. 2008 Jan 23;(1):CD000146.

3.     Hajek P, McRobbie H, Gillison F. Dependence potential of nicotine replacement treatments: effects of product type, patient characteristics, and cost to user. Prev Med. 2007 Mar;44(3):230-4. Epub 2007 Jan 4.

4.     Bjartveit K, Tverdal A. Health consequences of smoking 1-4 cigarettes per day Tobacco Control 2005; 14: 315-20, based on follow-up of 43,000 Norwegians from 1970s to 2002.

5.     Heeschen C, Jang JJ, Weis M, Pathak A, Kaji S. et al. Nicotine stimulates angiogenesis and promotes tumor growth and atherosclerosis. Nat Med. 2001 Jul;7(7):833-9.

6.     Lee CH, Huang CS, Chen CS, Tu SH, et al. Overexpression and Activation of the {alpha}9-Nicotinic Receptor During Tumorigenesis in Human Breast Epithelial Cells. J Natl Cancer Inst. 2010 Aug 23. [Epub ahead of print]


Cigarette cancers kill 1700 New Zealanders annually – 23% of all fatal cancers are due to cigarette smoking.

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