Does nicotine cause cancer? Or is the smoke from burning plant material? Smoking causes cancer, okay, but nicotine itself?
Does nicotine cause cancer?
By Jonathan Foulds, MA, MAppSci, PhD
Every now and again we see a new newspaper headline claiming that nicotine causes some serious health problem, whether it be heart attacks or cancer. Usually the headline is based on a very small study in humans, or a laboratory study of cells in a petri dish or test tube. In the past week we saw the latest example. A study by Gemenetzidis and colleagues in London examined the effect of nicotine on a protein transcription factor named FOX-1 in tissue cells in the laboratory. Fox-1 expression has been associated with onset of tumor growth in prior studies. The study found that nicotine application to cells in the lab resulted in an increase in Fox-1 expression (in the laboratory, not in humans). The authors therefore concluded that nicotine , by stimulating FOX-1 expression, may promote cell instability and tumor growth.
The thing that is relatively new about this finding is that many prior studies and reviews have concluded that nicotine does not play a part in stimulating tumor development or growth. So for this study to claim that nicotine causes cancer is contrary to previous expert opinion.
I am not a cell biologist and cannot claim to fully understand the science contained in this recent publication by Gemenetzidis and colleagues. However, I can think of some ways of assessing whether the laboratory finding really does translate into health effects in the real world. In many countries around the world people use smokeless oral tobacco for most of their adult life. Oral smokeless tobacco delivers high quantities of nicotine (in addition to other proven carcinogens), but without delivering any smoke. In Sweden there is a tradition of men using a form of smokeless tobacco, called snus, that is relatively low in other toxins. So if nicotine really does have a role in increasing oral cancer risk, we would assume that people using this nicotine delivery product throughout their whole life would have an increased oral cancer risk. However, numerous long term epidemiological studies of Swedish men who use this oral tobacco product have found that they do not have an increased rate of oral cancer, as compared with men who never used any tobacco products.
Gemenetzidis and colleagues, on the basis of their lab study of cells in the lab, have cautioned against the use of nicotine replacement therapy in case it causes cancer. Now nicotine replacement therapy is typically used for up to 12 weeks, but occasionally for longer. But NRT typically delivers lower levels of nicotine than snus smokeless tobacco and is almost never used in a lifelong fashion ….daily from teenage years for life, as is common for smokeless tobacco. So to my way of reading the epidemiological evidence, if lifelong use of high nicotine oral tobacco does not increase the risk of oral cancer, then the risk that a few months of NRT use will cause oral cancer are non-existent. So no, I don’t believe that this study provides convincing evidence that nicotine causes cancer.
Sometimes I wish that lab scientists would check out the epidemiological evidence before announcing to the press that effective therapies may cause cancer.
Example article last week in the London Times:
timesonline.co.uk
The full study report can be viewed at:
dx.plos.org
For a very thorough review of the health effects of nicotine, and of smokeless tobacco, check out the relevant chapters of the recent Royal College of Physicians report on tobacco harm reduction at:
rcplondon.ac.uk
healthline.com
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From Wikipedia:
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However, in a few situations, smoking has been observed to be of therapeutic value. These are often referred to as " Smoker’s Paradoxes". [78] Although in most cases the actual mechanism is understood only poorly or not at all, it is generally believed that the principal beneficial action is due to the nicotine administered, and that administration of nicotine without smoking may be as beneficial as smoking, without the higher risk to health due to tar and other substances found in tobacco.
For instance, studies suggest that smokers require less frequent repeated revascularization after percutaneous coronary intervention(PCI). [78] Risk of ulcerative colitis has been frequently shown to be reduced in smokers on a dose-dependent basis; the effect is eliminated if the individual stops smoking. [79] [80] Smoking also appears to interfere with development of Kaposi's sarcoma in patients with HIV. [81]
Nicotine reduces the chance of preeclampsia, [82] and atopic disorders such as allergic asthma. [83][ dubious – discuss] A plausible mechanism of action in these cases may be nicotine acting as an anti-inflammatory agent, and interfering with the inflammation-related disease process, as nicotine has vasoconstrictive effects. [84] An obvious bias to this study is selection bias as persons with more severe asthma are less likely to adopt a habit of smoking due to exacerbation of their condition in response to exposure.
While tobacco smoking is associated with an increased risk of Alzheimer's disease, [85] there is evidence that nicotine itself has the potential to prevent and treat Alzheimer's disease. [86] Nicotine has been shown to delay the onset of Parkinson's disease in studies involving monkeys and humans. [87] [88] [89] A study has shown a protective effect of nicotine itself on neurons due to nicotine activation of a7-nAChR and the PI3K/Akt pathway which inhibits apoptosis-inducing factor release and mitochondrial translocation, cytochrome c release and caspase 3 activation. [90]
Studies have indicated that nicotine can be used to help adults suffering from autosomal dominant nocturnal frontal lobe epilepsy. The same areas that cause seizures in that form of epilepsy are responsible for processing nicotine in the brain. [91]
Studies suggest a correlation between smoking and schizophrenia, with estimates near 75% for the proportion of schizophrenic patients who smoke. Although the nature of this association remains unclear, it has been argued that the increased level of smoking in schizophrenia may be due to a desire to self-medicate with nicotine. [92] [93] Other research found that mildly dependent users got some benefit from nicotine, but not those who were highly dependent. [94]
Research at Duke University Medical Center found that nicotine may improve the symptoms of depression. [95] Nicotine appears to improve ADHD symptoms.
People with ADHD smoke cigarettes at rates significantly higher than others, and start smoking earlier, smoke more, and have more difficulty quitting. Research is ongoing to understand if the brain conditions underlying ADHD make people more prone to nicotine addiction, if the nicotine has some therapeutic value, or if there is no causation underlying the correlation. [96]
While acute/initial nicotine intake causes activation of nicotine receptors, chronic low doses of nicotine use leads to desensitisation of nicotine receptors (due to the development of tolerance) and results in an antidepressant effect, with research showing low dose nicotine patches being an effective treatment of major depressive disorder in non-smokers. [97]
Nicotine (in the form of chewing gum or a transdermal patch) has been explored as an experimental treatment for OCD. Small studies show some success, even in otherwise treatment-refractory cases. [98] [99] [100]
The relationship between smoking and inflammatory bowel disease has been firmly established, but remains a source of confusion among both patients and doctors. It is negatively associated with ulcerative colitis but positively associated with Crohn's disease. In addition, it has opposite influences on the clinical course of the two conditions with benefit in ulcerative colitis but a detrimental effect in Crohn's disease.
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A plausible mechanism of action in some cases may be the nicotine in tobacco smoke acting as an anti-inflammatory agent and interfering with disease processes. [4]
Specific conditions[ edit]- Digestive system
- Cardiovascular system
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